DEVBIOL LE2 Transes (1) PDF - Developmental Biology Past Paper

DEVBIOL: DEVELOPMENTAL BIOLOGY Establishment of Germ Layers and Derivatives 2nd Term | AY 2022-2023 Made by: Matthew Mendoza Lecturer: Ms. Marigold Uba FORMATION OF GERM LAYERS Will experience further spli...

DEVBIOL: DEVELOPMENTAL BIOLOGY Establishment of Germ Layers and Derivatives 2nd Term | AY 2022-2023 Made by: Matthew Mendoza Lecturer: Ms. Marigold Uba FORMATION OF GERM LAYERS Will experience further splitting or deamination forming. o Epiblast → Embryonic epiblast ▪ This is where migration of cells happens moving towards the midline forming the primitive streak. ▪ With the morphogenetic movement of cells passing through the primitive streak, the following are formed. The structure above shows the primitive ▪ Embryonic endoderm formation. Embryonic, mesoderm & o You can see the epiblast and Notochordal process along hypoblast which are the results of the the midline process of deamination ▪ Cells that are left exteriorly o You can also see the movement of on top form the embryonic cells (morphogenetic movement of ectoderm. cells) via invagination passing Collectively, the throughout the primitive streak. formation of the 3 ▪ Some cells are moving embryonic germ downward displacing the layers is called as hypoblast → endoderm. trilaminar disc ▪ Some cells are engrossing formation. towards the blastocoel ▪ Amniotic ectoderm leading to the formation of o Hypoblast the embryonic mesoderm. ▪ Will give rise to the extra ▪ The cells that remain on top embryonic endoderm that will form the future ectoderm. will form the yolk sac RECALL Thus, the formation of epiblast and hypoblast is called as Bilaminar disc formation. B. Trophectoderm/ Trophoblast Will proliferate and increase in cell population forming o Cytotrophoblast (Contains the original cells of the trophoblast which are highly cellular and is responsible for the initial attachment of blastocyst to the uterine lining) Blastocyst- has two types of cells. o Syncytiotrophoblast develops A. ICM: Suspended in the blastocoel from the Cytotrophoblast. surrounded by the trophoblastic cells.  ▪ It is a layer that has lost o Contains spaces called lacunae cellular membrane such (for the proliferation of blood as the cells became a vessels forming the placenta) continuous layer ▪ Cells in this stage secretes enzymes that digest the uterine wall for information of the embryo o Extraembryonic mesoderm is derived from the Syncytiotrophoblast. The amniotic ectoderm, yolk sac, and the different components of the cytotrophoblast will form the large part of the placenta → thus forming the large part of the extraembryonic membranes. When the embryo is cut passing through the amniotic ectoderm above the embryonic epiblast, we can see the figure on the bottom left o Exposes the forming primitive streak. o The anterior forming oropharyngeal membrane. *Refer to the figure for the next set of texts o Wall of the yolk sac Epiblast: In the figure, it has already ▪ Derived from the undergone splitting forming the components of the embryonic epiblast hypoblast Amniotic Ectoderm: Is located on top of the epiblast. Hypoblast: Will expand laterally and moves downward over the blastocoel forming the yolk sac In the trophoblastic cells, you can see the thickening of a layer called Cytotrophoblast. o These contain the original cells of the trophoblast, dumami lang sila After further differentiation of the cytotrophoblast, syncytiotrophoblast is formed. The figure above shows the primitive streak o There are no longer distinct titled in an upright position to show the intracellular separation. movement of the surface epiblast o Cellular membrane are lost o Primitive node: Site of invaginating cells. Observe the  movement of the prenotochordal The figure shows a sagittal section (side cells cephalically. view) at the level of the primitive pit where the prenotochordal cells migrate (the blacken area in the figure) moving cephalically/ cranially If the primitive streak is cut cross sectional, The figure shows a cross section on the level you can see the site of inventing cells. of notochordal plate showing the migrating o Some are migrating downward to prenotochordal cells become intercalated in the hypoblast and displacing the the endoderm to form the notochordal hypoblast (forms the endoderm) plate. to the side forming the yolk sac o The other invagination cells undergo ingression occupying the blastocoel cavity →mesodermal cells. In the figure, it could be seen that the o Those left on top are the notochordal plate will detach itself from the ectoderm. endoderm to form the definitive notochord flung on the side by the extraembryonic mesoderm. Because of the formation of notochord proceeds from cranial to caudal, the definitive notochord is formed first at the cephalic region & progress to the caudal region. FORMATION OF THE 3 MESODERMAL SHEETS Notochord: It is derived from the Mesoderm Alt Name Fate prenotochordal cells which are from Para-axial Epimere Somite mesodermal origin Intermediate Mesomere Urogenital units FORMATION OF NOTOCHORD (CRANIAL- Lateral Plate Hypomere Somatic & CADUAL SEQUENCE) Splanchnic mesoderm REFERENCE POINTS  Look at the definitive notochord and on the Between the lateral plate mesoderm and side are the intraembryonic mesoderm. dorsal mesoderm (paraxial mesoderm), is o Note that the intraembryonic the intermediate mesoderm. mesoderm expands further to the sides & outside the embryonic region to form the extraembryonic mesoderm. In the 20 and 21 day old, observe the lateral plate mesoderm o The lateral plate mesoderm splits Form here, you can see the mesoderm into two ingressing towards the blastocoel ▪ Parietal Mesoderm ▪ Visceral Mesoderm o When both layers separate, it results to the formation of a cavity called embryonic coelom DEVELOPMENT OF THE SOMITE The figure above is a cross section of a 17- day old embryo. You can observe the definitive notochord and the mesoderm to the sides. Firstly, there is epithelialization of cells around a cavity. o Epithelialization- is the transformation of the embryonic cells into flat cells that are tightly packed With further development, the epithelial cell are transformed into mesenchymal type In the 19 day old, you can observe that the o There exist a mesenchymal-epithelial mesoderm expands to the sides forming the transition. lateral plate mesoderm  ▪ Cell loses epithelial Recall that the floor plate of neural tube and arrangement and become notochord secrete and express the genes loose. coding for shh (sonic hedgehog) and noggin ▪ In such, this cell migrates acts and formed the on the sclerotome around the notochord and The sclerotome expresses PAX1 gene which neural tube. controls the chondrogenesis and vertebrae ▪ Collectively, these cells form formation. the Sclerotome. The neural tube grove WNT proteins is REFERENCE POINT expressed activating PAX3 which demarcates the dermatome. WNT proteins also direct dorsomedial portion of somite which differentiate into muscle cell precursors. These muscle cells precursors (the dorsomedial and ventrolateral) express MYF 5 (muscle specific gene) The Neural Tube groove also expressed the gene NT3, activating the middorsal portion of the somite to form the dermis. WNT protein and BMP4 activate MyoD expression. o The muscle cells will ultimately form the myotome. ENDODERM FORMATION The dorsomedial cells and ventrolateral cells will form the myotome The remaining cell that are in between the dorsomedial cell and ventrolateral cells are called as the dermatome. Thus, the somite has 3 layers o Sclerotome: o Myotome o Dermatome From the figure above, you can see folding at the cephalic and caudal end (cephalocaudal folding) These folding will have an effect in the positioning of the ff: o Heart o Septum transversum o Yolk sac and amnion The formation of somite’s involved the interplay of genes  24- 28 day of the embryo, folding process proceeds and the opening of the gut tube into Shown in the figure are the further components the yolk sac narrows until it forms a connection of the endodermal layer. This leads to the formation of the vitelline duct. Seen on the left image is the digestive gut o Located between the midgut and yolk running from the stomodeum down to sac. proctodeum/ cloaca. o Where vitelline blood vessels are housed You can also see the out pocketing of the digestive gut, giving rise to the liver, gallbladder, REGION OF MESONEPHROS and pancreas Moreso, the divisions of the digestive gut such as the stomach and the intestines. Vitelline duct is also present and is connected to the yolk sac o There is also an out pocketing at the level of the hindgut, called the allantois Also derived from the endodermal layer are the pharyngeal pouches/ arch o Only 3 are seen on the figure above Mesonephros arise from the intermediate mesoderm. o One can observe the presence of the parietal and visceral mesoderm. o Visceral mesoderm forms a layer around the visceral organs whereas the parietal mesoderm form the lining of the body cavity o When these mesoderm splits, it results There are 4 gills slits/ arches present. to the formation of the intraembryonic o Each arches contain their respective cavity aortic arches, cranial nerve derivative, & Somatic/ parietal mesoderm gives rise to the skeletal derivative. body mesenteries that line body cavities. ▪ Take note of the figure above! Splanchnic/ visceral mesoderm give rise to various visceral organs of the body  Yellow is the pharynx. Blue is he pharyngeal pouch that lines the organs. Green are the pharyngeal folds/ slits Purple is the pharyngeal arches/ Branchial arches.  DEVBIOL (N02B) Week #8 Developmental Biology Lecture Topic: Neural Crest Cells Professor: Ms. Marigold O. Uba Figure 2. Migration of Neural Crest Cells. Neural Crest Cells NCC migrating to the cranial region forms the Neural Crest Cells components of the face & neck. ○ One of the primary derivatives of ○ Facial bones the ectodermal layer. ○ Facial cartilages ○ Derived from the brim of the neural ○ Facial connective tissues ectoderm during the process of NCC also gives rise to the pigment cells of neurulation. the skin, the melanocytes. ○ The term neural crest is indicative Adrenal medulla and sensory ganglia of the topographical location and (sympathetic & parasympathetic ganglia) origin of these embryonic cells. is also derived from the NCC. ○ NCC are pluripotent cells - Capable of giving rise to various cell types in Neural Crest Cells Migration Pathways the embryonic body. Neural crest cells are dependent on two ○ “Migratory cells” from factors: migration pathway/route & neuroectoderm. micro-environment of their final Have the characteristics of destination. mesenchymal cells ○ Neural crest cells forming (loosely-arranged) which melanocytes (pigment cells) follow allows them to move the lateral migration pathway. (ameboid movement). ○ Neural crest cells giving rise to ○ Undergo Epithelial-mesenchymal ganglia (dorsal root & sympathetic transition ganglia) follow the medial migration Performed when giving rise pathway. to different cell types in the body. Figure 1. Neural Crest Cells. The arrows indicate movement of neural crest cells away from the brim of the Figure 3. Neural Crest Migration Pathways & Crest-Derived forming neural tube. Migration occurs Tissues. before the final closure of the neural tube. Neural crest cells forming on the crust of the forming neural tube migrates downward and follows different routes to get lodged in their target organs. ○ Target Organs - Final locations where the NCC gets to settle.  Once settled, NCC will undergo final differentiation via cell-cell signaling. Figure 6. Fluorescent Photomicrographs of Anterior Sclerotome Four Overlapping Domains Figure 4. Directed Cell Migration of Vertebrate Neural Crest. Table 1. Four Overlapping Domains of Neural Crest Pathway 1 - Neural crest cells travel Cells. ventrally through the anterior sclerotome. DOMAIN Derivatives ○ NCCs following Pathway 1 and get lodged in the anterior sclerotome of Cranial Pigment Cells, Sensory Ganglia, Parasympathetic Ganglia, somite will participate in the Hormone-producing Cells, Glia formation of the cartilages and Cells. bones of the vertebral column. Forebrain & Midbrain → ○ There are no NCCs in the posterior Frontonasal Process, Palate, Incus, sclerotome of the somite as NCCs Malleus, Jawbones. are concentrated in the anterior Bones & Connective Tissues of the sclerotome. Head. Pathway 2 - Neural crest cells take a Certain structures within the eyes, dorsolateral route between the epidermis ears, and teeth. and the dermomyotome. SUBDOMAIN Septum between Pulmonary Arch ○ They get lodged under the Cardiac NC & Aortic Arch. epidermis and above the (Located in between Cranial & Vegal) Endothelium (innermost layer; lines dermamyotome the lumen of these arteries) of Aortic ○ NCCs following Pathway 2 will form Arch Arteries. the pigment cells of the body. Vagal Gives rise to various cell depending on the migratory pathway: Trunk DORSOLATERAL PATHWAY Lumbosacral Melanocytes, Neurons, Cartillages, & Connective Tissues. VENTRAL PATHWAY Dorsal Root Ganglia, Sympathetic Ganglia, & Parasympathetic Figure 5. Pathway 1 & 2 of Neural Crest Cell Migration. Ganglia. Figure 6. features cross section Schwann Cells & Adrenal Medulla photomicrographs which are stained with Derivatives of the cranial, vagal, trunk, and fluorescent dye. lumbosacral domains depend on the ○ Fluorescent bodies indicate the migratory pathway. concentration of NCCs in the anterior sclerotome of the somite.  Figure 9. Embryo - Week 5: Migration of the Cardiac Neural Crest Figure 7. Four Overlapping Domains. Migratory Paths of NCC in the Head Region Overlapping Domains NCC leaves the crests area of the neural Cranial NCC → Pharyngeal Arches, Face & folds prior to neural tube closure. Neck. Migrate to form structures in the: Cardiac NCC (Somites 1-3) → Septum ○ Neck and Face. between PA & Aorta. ○ Pharyngeal Arches (1-6). Trunk NCC (Somite 6 to Tail) → ○ Epibranchial Placodes (V, VII, IX, & Sympathetic neurons. X). → eventually generates neurons Vagal NCC (Somite 1-7) and ganglia Sacral NCC (Posterior to Somite 28) → Parasympathetic Nerves of Gut. Somite 18-24 → Adrenal Medulla. Figure 10. Pharyngeal Arches Cranial NCC from Rhombomere Regions Gives rise to different embryonic structures depending on the level of the rhombomere they’re coming from. Figure 8. Four Overlapping Domains 2. Figure 9 shows the migration of the cardiac R 1&2 migrate → 1st Pharyngeal Arch; neural crest cells from the neural tube area they participate in the formation of: going downward to the developing ○ Jawbones embryonic heart. ○ Ear Bones The aortic arch is the forming septum ○ Frontonasal Process which will eventually be colonized by the R 4 migrate → 2nd Pharyngeal Arch; cardiac neural crest cells to form the formation of: septum. ○ Hyoid Cartilage. Aortic arch arteries are lined with R 6 migrate → 3rd & 4th Pharyngeal arch migrating cardiac neural crest cells. and pouches; formation of: ○ Thymus ○ Parathyroid ○ Thyroid  R 3&5 do not migrate through the with the closure of neural surrounding mesoderm → Stay on either tube side of the rhombomere mesoderm. Before the neural tube has NCCs- are also sometimes referred to as closed, the gene product of the 4th germ layer as many arise from them SLUG has already activated the migration of NCCs away from the neuroectoderm How is Migration Initiated? Presence of BMP 4&7 ○ High concentration of BMP 4 & 7 induces the expression of RhoB & Slug genes (protein products). ○ These protein products: Figure 11. Neural Plate Formation. Establish cytoskeletal During neural plate formation, there is conditions that promote concentration of signaling molecule BMPs migration of NCC in the junctional border of surface From slug genes: Activate ectoderm in the neural plate. factors that dissociate the Different concentrations of BMPs tight junction in between influence the development or fate of the the cells. embryonic ectoderm. Loss of N-cadherin (cell-adhesion ○ High Level → Induces epidermis molecule) that links neural crest cells formation. ○ With the loss of N-cadherin ○ Intermediate Level → Induces molecules, the neural crest cells neural crest cells formation. may undergo amoeboid movement. ○ Low Level → Induces neural ectoderm formation. How Do Migratory Agents Know The Route On Which To Travel? Regulation of NCC Induction Path of the NCC is controlled by the Extracellular Matrix BMPs is not the sole signaling molecule of ○ Components of ECM: NCC induction, it interplays with other Promote Migrations - signaling factors like fibroblast growth “Substrate-Adhesion factor and WNT proteins. Molecules” (SAMs) Immediate concentration of BMPs Substrate-Adhesion (together with FGF & WNT proteins) Molecules (SAMs) - induce PAX3 & other transcription factors Provide contact that specify the neural plate border. guidance for the PAX3 & other transcription factors that migration pathway specify the neural plate border triggers the of the embryonic 2nd wave of transcription factors: cells. ○ SNAIL & FOXD3 which specify cells Promote migrations as neural crests. ○ Examples: ○ SLUG which promotes NCC Fibronectin, migration from neuroectoderm. Laminin, Timing of activation of Tenascin, SLUG is almost simultaneous Collagen Molecules,  Proteoglyca ○ Can control the activity of the other ns. genes under them. Restrict Migrations ○ Can specify the general body plan Examples: Ephrin of the embryo Proteins - Expressed Hox genes have the task of organizing the in the posterior body plan of an animal. portion of the Hox genes are a particular subfamily of sclerotome homeobox containing genes that evolved Chemotactic and Maintenance Factors together with a complex multicellular body ○ Soluble factors secreted by plan. potential destinations. Evolutionary conserved from vertebrates ○ Same signaling factors in the to invertebrates. micro-environment of the final They are utilized to convey positional locations of the NCC that will information and organize the body plan: influence the final differentiation. ○ Examples: Stem Cell Factors 3 FEATURES OF HOX GENES Allow continuous 1) They contain a subclass of highly proliferation of NCC. conserved homeobox sequences, so they encode transcription factors Final Differentiation of Trunk NCC 2) They are involved in organizing the body plan of an animal Determined by the environment into which 3) They exist in clusters of similar genes in the they migrate and settle genome ○ Cell-signaling Factors (will determine the final differentiation of NCCs) TGF-ß superfamily Growth factors Examples: ○ BMP2 (Secreted by the lungs, heart, dorsal aorta): NCC Differentiate → Cholinergic Neurons → Sympathetic Ganglia in the Neurons. ○ Endothelin-3 NCC → Melanocytes NCC → Adrenergic Figure 12. Hox Genes in Drosophila melanogaster. Neurons in the Gut. Hox A & G located in chromosome 6. ○ Glucocorticoids: NCC → Hox B located in chromosome 11. Adrenomedullary Cells. Hox C located in chromosome 15. ○ FGF (Fibroblast Growth Factor): Hox D located in chromosome 2. NCC → Sympathetic Neurons. Paralogous Chromosomes - Similar genes but located in different chromosomes. Orthology - Genes found within the same What Specifies The Fates of NCC? cluster of genes. Combination of Hox genes (The genes that Expression of Hox genes during specify A-P axis) development are in the cephalic to caudal ○ Code for homeodomains region. (transcription factors, at the highest hierarchy of the genes).  If anterior genes are expressed earlier, posterior genes are expressed later. ○ If misregulation or abnormality occurs in the cephalic end the anterior genes are at fault. DEVBIOL (N02B) Weeks #8-9 Developmental Biology Lecture Topic: Implantation, Fetal Membrane, and Placentation (Part A) Professor: Ms. Marigold O. Uba These folds (head fold, tail fold, and & EXTRAEMBRYONIC MEMBRANES lateral body folds) scoop up the developing embryo from the underlying yolk mass Recap on Previous Topic The blastoderm (in avians) and the ICM (in mammals) is where the primitive streak forms ○ When the primitive streak is already there, both the epiblast and hypoblast delineate Membranes that do not enter into embryo ○ This is followed by morphogenetic formation, temporarily nor permanently movement, resulting into the ○ In other words, membrane tissues formation of the endoderm, that do not participate in the mesoderm, and ectoderm formation of the embryo proper neither temporarily nor permanently ○ Their only function is to provide care and maintenance to the embryo, such as nourishment, protection, respiration & excretion There are 4 groups: ○ Yolk sac Recap on development of the extraembryonic ○ Amnion membranes ○ Chorion Refer to the diagram below: ○ Allantois Some of those morphogenetically moving cells form the endoderm (yellow part above Development of the extraembryonic the yolk sac) membranes The others form the mesoderm At the start of embryonic development, the (pink/purple part) extraembryonic membranes are not Those left on top = ectoderm (blue part) distinct from the embryonic tissues ○ They become highly specified & distinct only upon the formation of the body folds Formation of body folds: ○ Head fold - cephalically ○ Lateral folds - sides ○ Tail fold - caudally Endodermal cells = spread downward, occupying the yolk mass Mesoderm = spread outward from the region of the embryo (pink/purple part) to become extraembryonic mesoderm  Likewise, the ectoderm spreads outside Summary (blue part) away from the region of the Extraem Origin Innermost Outermost embryo bryonic layer layer membra ○ Eventually, it forms a hood above nes the developing embryo (which is the amnion) Amnion Somatopleuric Ectoderm Mesoderm Chorion Extraembr Ectoderm yonic mesoderm Yolk Sac Splanchnopleuric Endoderm Extraembry onic mesoderm Allantois Endoderm Extraembry Amnion moves outward as chorion onic Mesoderm Diagram Analysis Amnion has ectoderm as the innermost and mesoderm as the outermost ○ Pink/purple = somatopleure Chorion has ectoderm as the outermost and extraembryonic mesoderm as the innermost Amnion & chorion = somatopleuric in Somatopleure = forms a somatopleuric origin with ectoderm and extraembryonic hood over the developing embryo mesoderm ○ That will eventually form the For the yolk sac, it has endoderm as the amnion innermost layer & extraembryonic The amnion flares outward mesoderm as the outer layer to form the chorion Allantois = “outpocketing” of the hindgut So the amnion and the ○ Caudal end (yellow) = lined with chorion are made up of endoderm & outside by the ectoderm & mesoderm extraembryonic mesoderm On the other hand, the endoderm spreads Yolk sac: endoderm & mesoderm over the yolk mass to form the yolk sac Allantois: endoderm & mesoderm, similar ○ The yolk sac remains connected at with the yolk sac the level of the middle part of the Yolk sac and allantois = splanchnopleuric primitive gut; it exists as the yolk in origin stalk The hindgut (posterior end of the primitive gut) forms an outgrowth, the allantois ○ Similar to the yolk sac, the allantois, because it is an extension of the hindgut, this is lined with endoderm, fused with the extraembryonic mesoderm  Amnion & chorion = somatopleuric in origin Yolk sac & allantois = splanchnopleuric in origin Derivation of the extraembryonic tissues in Figure above: embryo that is lifted placental mammals up/scooped up from the underlying yolk mass At the level of the midgut, this is the yolk sac connected via the yolk stalk This is an outpocketing of the hindgut = allantois Allantois is lined with endoderm and an outer extraembryonic mesoderm Amnion = forms a hood over the developing embryo; it flares outside as the chorion Chorion encompasses all the other 3 If you were to trace the inner cell mass extraembryonic membranes (pinakalabas si delaminating into the epiblast & the chorion) hypoblast ○ The hypoblast during gastrulation = when the morphogenetically moving cells move strictly downward, and displace the hypoblast ○ From thereon, the endodermal cells spread downward over the yolk mass to form the yolk sac Figure above: also developing embryo ○ Yolk sac is lined with scooped up connected to the yolk sac via extraembryonic endoderm the yolk stalk This is the first Similar descriptions of yolk sac, amnion, extraembryonic membrane allantois, and chorion as previous figure that makes its appearance ○ Meanwhile the epiblast is where the primitive streak forms The epiblast delaminates into the embryonic epiblast and the amnion The amnion is made up of ectoderm When the primitive streak is formed, what happens next is morphogenetic movement  of cells passing through the primitive node of the primitive streak ○ There will be formation of embryonic endoderm & embryonic mesoderm ○ Embryonic endoderm = displaces the hypoblast that spreads over the yolk sac ○ Embryonic mesoderm = also flares outside to the sides as the extraembryonic mesoderm Extraembryonic mesoderm, extraembryonic endoderm, and amniotic ectoderm = form a large part of the Development of mammalian embryo placenta, of course together with the ○ Viviparous development differentiated cells originating from the (development within the mother) trophoblast (this is for placental ○ In mammalians, because of mammals) viviparity, development inside the Avians & mammalians = both classified as mother = the yolk rather is vestigial amniotes because of the presence of the (just a remnant); nevertheless, the extraembryonic membrane yolk sac is evolutionarily conserved Both oviparous and viviparous development of vertebrates both contain 4 Four sets of ExEM sets of extraembryonic membranes In placental mammals, yolk sac is evolutionarily conserved ○ Amnion, chorion, and the incorporation of the allantois into the umbilical cord Amnion forms a hood around the developing embryo ○ This is made up of ectoderm and The Extraembryonic Membranes mesoderm The mesoderm of the amnion flares outside between the amnion and the trophoblastic layer ○ This layer between the amnion and the trophoblastic layer makes up the chorion ○ Similar of that with the avian extraembryonic membranes, chorion encompasses all the other three extraembryonic membranes; it surrounds the amnion, yolk sac, and allantois Allantois (in mammalian placenta) is not Development of the chick embryo shown because it is incorporated in the ○ Oviparous development umbilical cord / inside the umbilical cord (development outside the mother) ○ In avians, there is a massive amount of yolk  Yolk sac ○ Having its fluid, it functions like a shaker, so it buoys* the developing embryo in that amniotic fluid, so that during organogenesis, the organs will not stick together; it functions like a shaker in cell culture set-up in microbiology ○ Presence of fluid also provides protection to the embryo against mechanical stress First membrane to make its appearance Grows over the yolk mass Chorion Functions: ○ Change yolk into soluble materials for the embryo Yolk materials deliver it to the embryo via the open midgut, passing through the yolk stalk ○ Endodermal cell lining (of the blood vessels) as site of synthesis of the first serum proteins The yolk sac is an embryonic Functions: site of hematopoiesis ○ In chick: (generation of blood cells & 1) transport Ca2+ egg shell blood vessels) into the embryonic ○ Site of the primordial germ cell circulation → beak & (PGCs) specification skeleton 2) exchange of respiratory Amnion gases Acts as respiratory site ○ In mammals: respiration, filtration, hormone production (forms large part of placenta) Allantois Encloses the embryo in a fluid filled cavity (amniotic cavity) Extraembryonic membrane most intimate with the embryo; it surrounds the embryo in a cavity filled with amniotic fluid Function: ○ Fluid content protects the embryo Evagination from ventral wall of hindgut from adhesions and mechanical *** its mesoderm fused with the chorion stress and to some extent with amnion  Functions: ○ It surrounds a cavity now (amniotic ○ “Chorioallantoic membrane” as cavity) efficient respiratory structure (once ○ It now separates the inner cell mass it has fused with the chorion) from the trophoblast ○ Reservoir for excretory wastes ○ Amnion now separates the ICM Birds & reptiles: sequester from the trophoblast nitrogenous wastes Humans: contribute to vascular network of placenta Note: allantois is the hard white part in balut Day 10 Reference point = blastocyst with the inner cell mass, the trophoblast and the blastocoel Gastrulation proceeds, increase in the population of cells, forming the endoderm Increase in the population of cells, forming the mesoderm With more mesodermal cells forming, mesodermal cells move to the sides away from the area of the embryo as The formation of the yolk sac and the amnion (above extraembryonic mesoderm (pupunta siya figure) diyan, pupunta siya dito) Embryonic epiblast: color blue So the yolk sac endoderm is overlayed with Hypoblast: color yellow, beside embryonic extraembryonic mesoderm epiblast The extraembryonic mesoderm flares ○ The hypoblastic cells are displaced outward and forms a union overlying the on the side, colonized by the amnion endoderm, and the endoderm The amnion now has an inner layer of spreads over the yolk mass, ectoderm and an outer layer of mesoderm collectively forming the yolk sac endoderm On the other hand, the epiblast delaminates to form the amniotic ectoderm, forming a helmet or a hood over the developing embryo, so the primitive streak will develop in the epiblast ○ Embryonic epiblast, and then the amnion Formation of the allantois and the chorion ○ Eventually, the connecting stalk, together with the yolk sac stalk, will be wrapped with amnion. This will make up the umbilical cord. Placenta Site of physiological exchange between mother and embryo Composed of: ○ Fetal tissue - furnished by Formation of the chorion extraembryonic membranes ○ In placental mammals, chorion is (largely contributed by the chorion) the combination of the ○ Maternal tissue - furnished by extraembryonic mesoderm and the uterine endometrium cytotrophoblast It is a fusion of extraembryonic membranes ○ The extraembryonic mesoderm and lining layers of the uterus flares outside and separates the In other words, it is made up of maternal cellular trophoblast / tissue contribution and embryonic tissue cytotrophoblast from the contribution blastocoel Formation of the allantois ○ At the caudal end, at the level of the Types of placenta based on the degree of contact of placental component hindgut, there is a formation of an outpocket (bulge). It is lined with Deciduous placenta endoderm and overlaid with ○ At the time of parturition of giving extraembryonic mesoderm birth of the young, the uterine tissues are damaged and shed-off; bleeding occurs Week 3 to Week 5 ○ Villi are embedded within the endometrium. The villi are being pulled during birth that’s why it is a bloody parturition. ○ Intimate contact Note: The umbilical cord is not exactly the same as the allantois The chorion will eventually form a Non-deciduous placenta connecting stalk which will form a ○ At the time of parturition, the connection with the maternal component uterine tissues are NOT damaged of the placenta. This is also called the nor shed off. If there is, it’s very chorionic stalk (connecting stalk). minimal. ○ The connecting stalk houses blood ○ Villi are NOT embedded within the vessels (arteries and veins) and the endometrium. Because of the loose allantois connection, this is not a bloody parturition  ○ Loose contact Zonary ○ Contact involving girdlike band Types of placenta based on shape and (girdle) encircling the blastocyst; distribution of placental villi on the the villi are arranged in transverse chorionic sac enclosing the fetus zones and penetrate the uterine Diffuse wall ○ Greater part of chorion surface ○ Ex.: carnivores, cats, dogs associated with the uterine endometrium; the villi are spread out ○ Ex.: pig Discoidal Cotyledonary ○ Contact is restricted to a disc or ○ Contact is restricted to the plate; the villi form a disc that is localized patches of villi called intimately connected to the uterine cotyledons wall ○ Ex.: sheep, cow, deer ○ Ex.: primates, humans, some rodents, rabbits  Types of placenta based on histology According to the number of layers of cells separating fetal circulation from maternal Tissue Barriers circulation. Black arrows show the flow of blood from maternal and fetal tissues. Orange line represents the placenta which is the point of exchange. Further illustration based on the remaining maternal layers in the three types of placenta ○ Epitheliochorial (A) - has all the tissue barriers ○ Endotheliochorial (B) - only the maternal/uterine endothelium is retained ○ Hemochorial (C) - all the maternal Epitheliochorial type - the most superficial; endothelium is gradually lost lacks significant invasion of the uterine lining Syndesmochorial type - endometrial epithelium is removed at implantation; unusual type of placenta Endotheliochorial type - maternal uterine epithelium and connective tissue disappear at implantation Hemochorial type - the most invasive type; all maternal tissue layers disappear; there is a direct connection between chorion and maternal blood  Types of placenta based on architecture Labyrinthine placenta in rodents of the chorionic membranes in contact with maternal tissues Folded ○ Ex.: swine ○ Chorionic folds line the wrinkled surface of uterine epithelium ○ Chorionic folds in black box in the figure below Cross sections and histological features of different types of placenta Villous ○ Ex.: primates and ruminants ○ Chorion develops into finger-like extensions called villi (1°, 2°, 3°–these refer to the degree of branches) Labyrinthine ○ Ex.: rodents ○ Chorion develops a meshwork ○ Feto-maternal space (labyrinth) forms a network (merging of the chorionic villi surrounding maternal blood lacunae) ○ Fetal blood cells are nucleated, maternal blood cells are non-nucleated  DEVBIOL (N02B) Weeks #8-9 Developmental Biology Lecture Topic: Implantation, Fetal Membrane, and Placentation (Part B) Professor: Ms. Marigold O. Uba Recall: Three layers of the uterus: FORMATION OF THE PLACENTAL COMPLEX 1) Endometrium - layer involved in placental : occurs after the establishment of the formation extraembryonic membranes a) Endometrial surface - responsible for the formation of the placenta 2) Myometrium 3) Perimetrium The Basic Molecular Players in Placental 1) Implantation Establishment 2) Differentation of trophoblast 3) Formation of chorionic villi (fingerlike For simplicity, molecules below are only of structures in the chorion) primary focus but in reality, there are a lot 4) Decidual reaction (components of the of other molecules maternal tissues that are shed-off) 5) Matured placenta IMPLANTATION : takes place at around the 7th up to the 10th day : will be implanted around the uterus 1) cAMP (cyclic AMP) 2) hCG (human chorionic gonadotropin) - hormone for pregnancy test that starts to get secreted by the time the blastocyst is in the vicinity of the uterus Collective function of cAMP and hCG: 1) Direct cytotrophoblast differentiation towards a hormonally-active syncytiotrophoblast phenotype Other players: 1) LIF (Leukemia inhibitory factor) 2) TGF(Beta) - play a vital role for implantation process Cross-sections of the tubular uterus  DEVBIOL (N02B) Weeks #8-9 Developmental Biology Lecture Topic: Implantation, Fetal Membrane, and Placentation (Part B) Professor: Ms. Marigold O. Uba Collective function of LIF and TGF (Beta) Timeline/Milestone of Blastocyst Stage to - down regulate hCG synthesis and Formation of Amniotic Cavity upregulate TUN secretion Comparative GESTATION among vertebrates Rodents (mice and rat): usual animal models Day 6: Blastocyst Humans: 3 months Day 7: Implantation Horses: latest Day 8: Trophoblast Development : progressing invasion into the endometrial lining Following implantation is: Day 9: Formation of Amniotic Cavity : successful progressive invasion into the endometrial lining DIFFERENTIATION OF TROPHOBLAST 1) Inner cytotrophoblast : with very distinct cellular boundaries 2) Outer syncytiotrophoblast : highly cellular 1) Previllous stage - contains a core of : cellular boundaries are already lost mesenchymal cells that are loosely : formation of vacuoles and fusion of arranged vacuoles forming bigger cavities or spaces 2) Primary villi 2nd week (“lacunae”) 3) Secondary to tertiary villi 3rd week 4) Secondary to tertiary villi 3rd week  DEVBIOL (N02B) Weeks #8-9 Developmental Biology Lecture Topic: Implantation, Fetal Membrane, and Placentation (Part B) Professor: Ms. Marigold O. Uba Human embryonic disc at 18 days The extraembryonic membrane of the chorion enveloping the allantoic duct, the yolk sac duct and containing the villous capillaries all together enclosed as the umbilical cord Central parts of the umbilical cord: - The umbilical arteries originate from the villous capillaries - The umbilical arteries and umbilical veins plunged with the allantoic duct and the yolk sac duct (will eventually disappear) Allantoic duct - The allantois will form the urinary bladder Chorion - gives rise to the villi while the yolk sac within will become a Chorionic clay - made up of extraembryonic remnant or vestigial mesoderm Villous capillaries will inavde the intraembryonic area of the chorion fusing with the allantoic duct The site of exchange between the fetus and mother in the Placenta Chorion will then surround an allanotic duct and the capillary villus forming initially the connection between the developing embryo and the developing placenta as the “connecting stalk” or the body stalk Connecting stalk = allantoic duct + invading capillary villus Comparison of 6-week embryo vs 3-month old At the site of implantation, the decidual cells are specifically called “decidual basalis” Chorionic cells/ vesicle - overlaid by the amnion Amnion - encloses the fetus and amniotic cavity The well-developled chorionic villi = arise form the base as the chorionic plate or chorionic vesicle The supply of blood from the mother is via the developing spiral arteries unloading into the intervillus spaces, where the blood pressure of the mother is high thus facilitating the unloading of oxygen  DEVBIOL (N02B) Weeks #8-9 Developmental Biology Lecture Topic: Implantation, Fetal Membrane, and Placentation (Part B) Professor: Ms. Marigold O. Uba The blood then returns to the blood ciruclation of the mother passing through the maternal vein After unlodging of the oxygen-rich and nutrient-rich blood picked up the fetal circulation via umbilical arteries Likewise, the metabolite byproducts go back to the placenta of the mother (site of exchange) DECIDUAL REACTION Endometrium 1) Decidua basalis : transformation of the stromal cells of the 2) Decidua capsularis endometrium 3) Decidua parietalis Deciduum : collective term for the tissues that are shed at birth : extraembryonic tissues + superficial layers of endometrial connective tissue and epithelium Decidua basalis : where the implantation takes place and the basal plate is formed : lies between chorionic vesicle and uterine wall Decidua capsularis Organ Composition : forms a capsule around the chorionic vesicle D. Parietalis Non-implantation area of (vera) uterus Decidua parietalis Pro gravid endo. Potential but unused site of : the remaining decidua consists of: implantatio; outer ply of decidualized endometrium on the amnion D. capsularis Superficial part of the (refelexa) endometrium of pregnancy D. basalis Maternal placenta (serotina) Endometrium of pregnancy beneath chorionic sac Supplies maternal blood to placenta  DEVBIOL (N02B) Weeks #8-9 Developmental Biology Lecture Topic: Implantation, Fetal Membrane, and Placentation (Part B) Professor: Ms. Marigold O. Uba Chorionic tissue By this stage, the trophoblast cells have begun to make the hallmark hormone: Human chorionic gonadotropin (hCG) Organ Composition C. Laeve Smooth area of chorion Lacks villi, middle ply of IMPLANTATION amniotic sac 1) Floating blastocyst → become C. Frondosum Chorion attached to D. Basalis attached to the uterine lining Fetal portion of placenta (endometrium) 2) Blastocyst is first slowed down by long molecules (mucins) that extend from the endometrium 3) Cascade of molecules bring the trophoblasts into closer contact with the endometrium 4) Intimate contact is made → trophobalst cells invade into the endometrium (process of placentation) DAY 9 of Implantation site BLASTOCYST Stage Embryo surrounded by the 2 layers of trophoblasts: 1) Inner mononuclear cytotrophoblasts 2) Outer multinuclkeated synctiotrophoblast vacuoles form → fused into lacunae By 4-5 days after fertilization, the embryo (lacunar stage) differentiates into 2 distinct cell types 1) Inner cell mass This arrangement of embryo, trophoblasts and - Will develop into the maternal tissue remains the paradigm throughout fetus gestation 2) Trophoblasts - Will develop into the This arrangement of embryo, trophoblasts and placenta and maternal tissue remains the paradigm throughout external membranes gestation  DEVBIOL (N02B) Weeks #8-9 Developmental Biology Lecture Topic: Implantation, Fetal Membrane, and Placentation (Part B) Professor: Ms. Marigold O. Uba Trophoblast interface serves as: 1) The means to extract nutrients from the mother 2) Protects the embryo and fetus from maternalimmunologic attack DAY 12: IMPLANTATION SITE The basic structure of the placenta has been formed 1) Blastocyst completely embedded into With maternal blood beinf delivered to the forming endometrial stroma placenta via spiral arteries while being drained 2) The invading trophoblasts have penetrated away via uterine veins the maternal capillaries (sinusoids) 3) Form pools of maternal blood which The developing chorionic villi remian immersed in a surround the growing trophoblasts space filled with the nutrient-rich maternal blood BASIC STRUCTURE OF PLACENTA 3 weeks implantation site 1) The embryo has already begun to make an early circulatory system Spinal arteries and veins infiltrating the lacunae Continuation of the formation of the chorionic villi arising from the chorionic base orchorionic plate The embryo is enclosed in the amnion with amniotic fluid 2) Embryonic tissue and maternal blood separated by a layer of cytotrophoblasts and synctiotrophoblasts 4 weeks implantation site  DEVBIOL (N02B) Weeks #8-9 Developmental Biology Lecture Topic: Implantation, Fetal Membrane, and Placentation (Part B) Professor: Ms. Marigold O. Uba Placenta & membranes in multiple pregnancies Umbilical cord contains: umbilical arteries and veins + Wharton’s jelly (mesenchyme cells) Point of exchange is the placenta in the inervillus spaces DECIDUAL REACTION Identical twins Illustration of the mechanism of estrgen and oxytocin Identical (“monozygotic”) twins →involves only 1 oocyte but at the blastocyst stage, the ICM splits into two and will form an embryo enclosed in the same trophoblast Fraternal (“dizygotic”) twins → 2 different oocytes fertilized at the same time; develop synchronously; They will have their own decidua basalis for each embryo  DEVBIOL (N02B) Weeks #8-9 Developmental Biology Lecture Topic: Implantation, Fetal Membrane, and Placentation (Part B) Professor: Ms. Marigold O. Uba 2) Immunosupression, suppression of the mother’s immune response against the fetus Most of the antibodies needed by the baby are acquired from the mother directly Membrane permeability of placenta enables the transport of antibodies from the mother to the baby ESTROGEN For identical twins, splitting early becomes more During pregnancy, it stimulates the growth favorable because there is also a lesser chance of of the uterus and enhances the blood flow conjoining thus making them independent between the uterus and the placenta Causes the breast to enlarge as a FUNCTIONS OF THE PLACENTA preparation for milk production During baby delivery: 1) Physiological site of maternal-fetal It stimulates contractions of the uterus exchange muscle to help in pushing the baby out a) Fetal-maternal blood mixing i) Passive diffusion of blood gases - O2, CO2, N2 b) Facilitated diffusion of monosaccharides/glucose Progesterone: maintenance of the i) Main energy source; fetal endometrial lining maintains pregnancy glycemia is directly hCG (human chorionic gonadotropin): correlated with maternal maintains progesterone production until glycemia end of 1st trimester when the placenta c) Active transfer of amino acids produces P&E i) Diffusion of urea, ethanol hPL (human placental lactogen) ○ Influences growth, lactation, lipid 2) Works as endocrine gland and carbohydrate metabolism - The synctiotrophoblast cells of the placenta secrete 4 main kinds of hormones: 1) Estrogen 2) Progesterone PATHWAYS OF TROPHOBLAST 3) 2 horomnes peculiar to the DIFFERENTIATION placenta: hPL and hCG The cytotrophoblast- the stem cell of the 3) Immunological barrier placenta gives rise to the differentiated forms of trophoblasts 2 important roles in fetal-maternal immunologic Within the chorionic villi, cytotrophoblasts balance: fuse to form the overlying 1) Passive immunity synctiotrophoblast DEVBIOL (N02B) Weeks #8-9 Developmental Biology Lecture Topic: Implantation, Fetal Membrane, and Placentation (Part B) Professor: Ms. Marigold O. Uba The villous synctiotrophoblast makes the majority of the placental hormones, the most studied being hCG Cyclic AMP and its analogs, and more recently hCG itself have been shown to direct cytotrophoblasty differentiation towards a hormonally active synctiotrophoblast phenotype DEVBIOL (N02B) Week #9 Developmental Biology Lecture Topic: Hormonal Control Part A & B Professor: Ms. Marigold O. Uba successful in late HORMONAL CONTROL OF REPRODUCTION September, the birth of Vertebrate reproduction the offspring would occur towards the end of February or early March, which is in time for the onset of Spring. Environmental conditions are optimal. Case of Palolo worms - reproductive cycles are regulated by lunar cycles. At night, these palolo worms break their tails ○A cyclic activity that are engorged with ○Among lower vertebrates, it is often gametes. It would lead related to changing seasons to bursting and fill the ○ It is important for the survival of ocean surface with the species because the offspring milky gametes. must appear at times when environmental conditions are NEUROSECRETORY CELLS optimal for their survival Hormonal control ○ reproductive cycles (reproductive process) ○ Regulated by environmental cues (e.g., day length, seasonal temperature, amount of rainfall, and lunar cycles) Case of Female sheep - have a reproductive cycle that lasts for Hypothalamus 15 to 17 days, which means that ○ Synthesizes and secretes ovulation can occur in the 7, 8, Gonadotropin-releasing hormone. or 9th day (middle of the cycle) Via the portal vessels, these get These 17-day cycles transported to the pituitary glands start to occur at the and stimulate the release of end of summer. Gonadotropins/Gonadotropic In the mid-latitude, hormones. summer ends in The Gonadotropic September to early hormones are FSH (Follicle October. Day length Stimulating Hormone) and starts to decrease LH (Luteinizing Hormone). which causes ovulatory These act for the gonads to surges to start. synthesize and secrete their Gestation period own hormones, which are occurs about 5 months. testosterone (testes) and If the mating was estrogen (ovary).  FREQUENCY OF ESTROUS CYCLE DURING CYCLIC REPRODUCTIVE PATTERNS OF THE BREEDING SEASON VARIES MAMMALS Estrous cycle Monoestrous ○ Found in lower vertebrates ○ Single EC in a breeding season ○ Associated with more pronounced ○ Ex: dogs and foxes behavioral cycles than menstrual Diestrous cycles Polyestrous ○ Refers to the changes in the uterus, ○ Recurrence of EC in a breeding ovary, and vagina season ○ Ex: cat growling in the middle of the ○ Ex: mice, rabbits, and squirrels night chasing the female cat - pronounced behavior THE GONADAL STEROIDS AND THEIR ○ Estrus CONTROL Limited period of sexual Ovaries activity ○ In response to the Gonadotropic The only time the condition hormones, they produce Estrogen of the vagina permits Testes mating ○ Produces Testosterone ○ Stages/Phases of the Estrous Cycle → changes in the uterus, HORMONAL CONTROL AMONG MALES ovary, & vagina Proestrus - period of preparation; when the ovarian follicles are growing Estrus - when mating occurs; correspond with the time of ovulation; release of oocyte for fertilization Metestrus - period of repair Diestrus - changes becomes small and anemic; uterus goes back to its original state; cycle gets repeated Menstrual cycle Hypothalamus synthesizes and releases ○ Found in Anthropoid primates GnRH -> activates the pituitary gland via (including humans) the Hypothalamo-pituitary Portal vessel -> ○ Refers specifically to the changes the Anterior pituitary releases the that occur in the uterus, (“uterine Gonadotropic hormones FSH and LH -> cycle”) which determine the acts on the target organ, which is the testes menstrual cycle. -> FSH specifically acts and stimulates on ○ Changes in the uterus are c