2023 MSPC 231 Fertilization, Embryonic Origin of Tissues & Differentiation PDF

THIS LECTURE IS IN TWO PARTS PART A – FERTILIZATION AND EARLY DEVELOPMENT PART B – EMBRYONIC ORIGIN OF TISSUES, & DIFFERENTIATION 06/10/2023 FKA/UGMS/MSPC 231 1 06/10/2023 FKA/UGMS/MSPC 231 2  PART A FERTI...

THIS LECTURE IS IN TWO PARTS PART A – FERTILIZATION AND EARLY DEVELOPMENT PART B – EMBRYONIC ORIGIN OF TISSUES, & DIFFERENTIATION 06/10/2023 FKA/UGMS/MSPC 231 1 06/10/2023 FKA/UGMS/MSPC 231 2  PART A FERTILIZATION AND EARLY DEVELOPMENT 2023 MSPC 231 By Frederick K. Addai, Ph.D., FWACM Department of Anatomy UGMS, KORLE-BU, ACCRA 06/10/2023 FKA/UGMS/MSPC 231 3  PRE-REQUISITE KNOWLEDGE Spermatogenesis – with Oogenesis – specifically specific reference to how oocyte maturation, how large numbers of ovarian follicular cell spermatozoa are development, and produced throughout development of the uterine post-pubertal life lining (endometrium) occur in synchrony 06/10/2023 FKA/UGMS/MSPC 231 4  STUDENTS’ LEARNING OUTCOMES 1. The requirements for male and female gametes to meet and fuse At the end of the lecture, you 2. The processes by which male and female should be able gametes meet and fuse in fertilization. to understand 3. The uniqueness of secondary oocyte in the following. driving cleavage 4. Human development from zygote to blastocyst 5. Implantation 06/10/2023 5  EARLY HUMAN DEVELOPMENT (1) Commences with the zygote –produced by fertilization The zygote undergoes a series of unique mitotic divisions called CLEAVAGE Cleavage gives rise to a ball of cells that is transported from the oviduct into the cavity of the uterus 06/10/2023 FKA/UGMS/MSPC 231 6  EARLY HUMAN DEVELOPMENT (2) The daughter cells of cleavage are called BLASTOMERES The first 3-4 divisions do not involve the production of new protoplasm Cleavage starts with the 2-cell stage, then the 4-cell stage, 8-cell stage, 16-cell stage, etc. The blastomeres at the 16-cell stage form a ball called the MORULA 06/10/2023 FKA/UGMS/MSPC 231 7  THE REQUIREMENTS FOR ( IN VIVO) FERTILIZATION FERTILIZATION is 1. Coitus (or penile-vaginal sexual intercourse) resulting in male ejaculation - Fusion of and deposition of semen in the vagina spermatozoon with a 2. Competent spermatozoon –having secondary oocyte undergone capacitation and acrosomal (ovum) resulting in the reaction formation of a ZYGOTE 3. Healthy secondary oocyte – ovulated and able to cross-talk with spermatozoon (cellular signaling and receptor activation) - Has Three KEY requirements 06/10/2023 8  EJACULATION Male ejaculation – release of Semen may also be called semen containing spermatozoa ejaculate (noun) and secretions of prostate gland Volume in between 1.8 ml to 5.5 and seminal vesicles ml (average 3.5 ml) Male orgasm (ejaculation) is Contains 100 million indispensable for fertilization spermatozoa per ml 06/10/2023 9  FERTILIZATION - SPERM QUALITY IS DECISIVE To facilitate fertilization, spermatozoa must have the following crucial features. 1.Right quantity; minimum of 15 million per ejaculate (semen) 2. Less than 4% abnormality 3. Competent - normal morphology and capable of progressive forward movement in one direction 4. Capable of undergoing capacitation & acrosomal reaction 06/10/2023 10  SPERM MOTILITY 40% of sperms must be motile, capable of forward propulsion in one direction Primary ciliary dyskinesia (PCD) (immotile flagellum or Kartagener’s syndrome) 06/10/2023 11  OBSTACLES THAT SPERMS ENCOUNTER IN THE FEMALE GENITAL TRACT 1. Acidity of vaginal fluid (many spermatozoa die) 2. Viscosity and acidity of cervical mucus (weaken and trap many spermatozoa, notably abnormal ones) 3. Distance from the vagina through uterine cervix and cavity, to the ampulla of the oviduct 4. Ref. https://doi.org/10.5935/MedicalExpress.2 015.02.07 5. Must survive 30 min to 12 hr swim and up to 72 hr wait for ovum 06/10/2023 12  FERTILIZATION REQUIRES A HEALTHY SECONDARY OOCYTE (OVUM) Devoid of structural abnormalities (which are very rare). Must have the right number of chromosomes (22 autosomes + X) Must have completed 1st meiotic division prior to ovulation Must encounter competent sperm within 24 hours of ovulation A primary oocyte surrounded by corona radiata cells inside a mature follicle before ovulation 06/10/2023 13  CAPACITATION OF SPERMATOZOA Physiological changes spermatozoa must undergo to have the ability to penetrate and fertilize the secondary oocyte Changes occur via the sperm cell membrane in which receptors are made available through the removal of a glycoprotein layer 06/10/2023 14  OOCYTE CORONA RADIATA Corona radiata are ovarian granulosa cells of the cumulus oophorus that surround the secondary oocyte (ovum) A composite diagram showing changes the spermatozoon must undergo to be capable of fertilizing the secondary oocyte. 06/10/2023 FKA/UGMS/MSPC 231 15  ACROSOMAL REACTION Changes that the acrosomal cap undergoes in response to triggers (signalling molecules) Releases hyaluronidase from the acrosome to digest cumulus cells surrounding the oocyte Exposes acrosin bound to the inner acrosomal (sperm) membrane Also, the Involves release of neuraminidase 06/10/2023 16  FERTILIZATION – A MULTISTEP PROCESS Occurs in three sequential events 1. Penetration of corona radiata 2. Penetration of the zona pellucida 3. Binding and Fusion of the oocyte and sperm cell membranes *Slow block to polyspermy or zonal reaction triggered by release of cortical granules from oocyte 06/10/2023 17  FERTILIZATION The sperm head releases paternal chromosomes into the oocyte to form the male pronucleus The secondary oocyte (ovum) completes the PB second meiotic division and ejects the PN PN second polar body (containing 23 chromosomes but with very little cytoplasm) The fertilized oocyte retains 23 maternal chromosomes that form the female pronucleus Fertilized oocyte showing 2 pronuclei (PN) and the second polar body (PB) 06/10/2023 18  IMMEDIATE EVENTS OF FERTILIZATION 1. Completion of second meiotic division of oocyte; formation of female pronucleus & expulsion of secondary polar body 2. Formation of the zygote by fusion of the male and female pronuclei 06/10/2023 19  IMMEDIATE EVENTS OF FERTILIZATION 3. Determination of genetic sex of the zygote (XX = female; XY = male) 5. Introduction of genetic 4. Restoration of the diploid variation (via cross-over & independent assortment of chromosomes) number of chromosomes (23 + 23 = 46) 6. Initiation of cleavage of zygote 06/10/2023 20  POSSIBLE COMBINATIONS OF CHROMOSOMES Humans have 23 pairs of chromosomes. 223 = 8,388,608 That means that one spermatocyte or oocyte could produce 223 different gametes. Fertilization of any 2 gametes can produce a In addition, with possible combinations that zygote in so many can emerge from the pairing of an oocyte different ways and a sperm, the result is (223)2 possible combinations. (223)2 = Fertilization can produce a zygote with over 70 trillion 70,368,744,177,664 possible combinations of the 46 chromosomes from both parents Seventy trillion, 368 Compare with the total human population of eight billion, 744 million, 177 billion thousand and 664 06/10/2023 FKA/UGMS/MSPC 231 21  UNIQUENESS OF SECONDARY OOCYTE Has adequate cytoplasm to produce 8 daughter cells without synthesis of new protoplasm Has all enzymes and factors to drive mitosis without fresh synthesis Only cell capable of spontaneous multiple & sequential mitotic divisions 06/10/2023 22  CLEAVAGE Occurs within the oviducts No growth between divisions and the nuclear to cytoplasmic ratio decreases about 1000-fold (G1 is almost absent) Unusual cell cycles lacking, or having very short, G1 and G2 phases Cytokinesis can be unequal 06/10/2023 FKA/UGMS/MSPC 231 23  ZONAL REACTION Occurs when a spermatozoon comes into contact with the plasma membrane of the ovum It alters the properties of the zona pellucida making it impermeable to any other sperm This is the slow block to polyspermy and is triggered by the release of cortical granules from oocyte 06/10/2023 24  POLYSPERMY IN HUMAN Polyspermic fertilization – does not proceed beyond a few cleavages of the zygote The pre-embryo dies at or after the 8-cell stage 06/10/2023 25  MOLAR PREGNANCY 1. Hydatiform molar pregnancy – expulsion of either male or female pronucleus. 2. Expulsion of female pronucleus may coincide with polyspermic fertilization ✓ No foetus forms, huge masses of deformed trophoblastic tissue secretes large amounts of HCG. ✓ Partial molar pregnancy may have a non-viable foetus 06/10/2023 26  WEEK ONE POST-FERTILIZATION Cleavage to implantation Cleavage - Succession of rapid divisions resulting in large number of smaller cells (blastomeres) No synthesis of new cytoplasm; thus, fractionation of oversize single cell (zygote) Blastomeres are enclosed within the zona pellucida – otherwise monozygotic twining FKA/UGMS/MSPC 231 27 06/10/2023  BLASTOCYST (DAYS 5-9 PF) Formation begins about 5 days after fertilization A fluid-filled cavity appears in the morula, the ball of 16 blastomeres Transported via “ciliary escalator” in oviduct to uterine cavity Arrives in uterine cavity day 7-9 pf 06/10/2023 FKA/UGMS/MSPC 231 28  IMPLANTATION Process of attachment and invasion of the endometrium of uterus by the blastocyst (conceptus) Requires blastocyst to hatch out of the zona pellucida Trophoblast (outer cell mass) adheres to receptive endometrium (in secretory phase) 06/10/2023 29 FKA/UGMS/MSPC 231  RECEPTIVE ENDOMETRIUM Corpus luteum (CL) formed from the ovarian follicle that discharged the secondary oocyte at ovulation CL under stimulation of LH produces progesterone Progesterone stimulates the endometrium to change from proliferating to secretory phase Blastocyst hatching must coincide with mid-secretory endometrium 06/10/2023 FKA/UGMS/MSPC 231 30  BLASTOCYST-ENDOMETRIUM CROSS-TALK -RESULT Implantation consists of three stages: a) The blastocyst contacts the implantation site of the endometrium (apposition); b) (b) trophoblast cells of the blastocyst attach to the receptive endometrial epithelium (adhesion); and c) (c) trophoblast cells cross the endometrial epithelial basement membrane - invasion FKA/UGMS/MSPC 231 06/10/2023 31 IMPLANTED HUMAN CONCEPTUS IN SITU Marks commencement of pregnancy or conception; may elicit false bleeding Endometrium accumulates more fluid (becomes oedematous) Endometrial cells become larger and accumulate more nutritive substances; glycogen, lipid, GAGs, etc. Endometrial changes known as decidualization, and tissue is DECIDUA Under influence of progesterone and oestrogen 06/10/2023 FKA/UGMS/MSPC 231 32  THREE REGIONS OF DECIDUA Basalis – b/n implanted blastocyst and myometrium. Capsularis – covers implantation site and bulge of blastocyst, separates it from uterine cavity. Parietalis – the remainder of uterine lining Oestrogen stimulates a more viscous o CMP serves as mechanical and cervical mucus that solidifies to form a antibacterial barrier from vagina plug (CMP) o Raises questions about superfetation 06/10/2023 FKA/UGMS/MSPC 231 33  SITE OF IMPLANTATION Usually – body of the uterus, the upper part of the posterior wall near the midline Implantation anywhere outside the body of the uterus, known as ectopic pregnancy 06/10/2023 FKA/UGMS/MSPC 231 34  CASE OF ABDOMINAL PREGNANCY IN GHANA Supplementary video - https://kbthghana- Advanced secondary abdominal pregnancy - my.sharepoint.com/:v:/g/pers a case report onal/a_swarray- deen_kbth_gov_gh/EbqsUD RluFBIlfDoRWiVhlYBJCwl p R- Teresa A MENSAH1, Alex K BOATENG1, Kwaku 4MkzeJbR9LinA6w?e=j5Dn DOFFOUR-DAPAAH1, Isaac ERSKINE2, Jerry COLEMAN1, cq). Samuel A OPPONG3, Alim SWARRAY-DEEN3* Angiogram of tubal gestational sac 1 Department of Obstetrics & Gynaecology, Korle Bu Teaching Hospital, Accra, Ghana; 2 Department of Pathology, Korle Bu Teaching Hospital, Accra, Ghana; 3 Department of Obstetrics & Gynaecology, University of Ghana Medical School, Accra, Ghana 06/10/2023 FKA/UGMS/MSPC 231 35  SUMMARY (1) 1. Requirements for spermatozoa and Zona reaction, fusion of male and female secondary oocyte to meet and fuse pronuclei, formation of zygote Coitus, male ejaculation, competent 3. Restoration of diploid chromosomes, spermatozoa, healthy ovum determination of genetic sex of zygote, the introduction of genetic variation 2. Processes by which spermatozoa and secondary oocyte meet and fuse 4. Secondary oocyte unique in spontaneously undergoing cleavage, first Sperm-specific: transport, capacitation, four divisions without synthesis of new acrosomal reaction, penetration of protoplasm corona radiata & zona pellucida, fusion of sperm membrane with plasma 5. Fate of polyspermic zygote and membrane of secondary oocyte hydatiform molar pregnancy 06/10/2023 36  SUMMARY (2) 6. Early development involves CLEAVAGE of the zygote, formation of MORULA, and subsequently BLASTOCYST 7. Blastocyst is transported from the oviduct ampulla (where fertilization usually occurs) to the uterine cavity 8. Cross-talk between the trophoblast of the blastocyst and the endometrium results in adhesion, erosion, and embedding of the blastocyst into the endometrium = implantation 9. Implantation outside the body of the uterus is ectopic 10. Endometrium responds to implantation to become decidua 11. Three regions of decidua are distinguished as basalis, capsularis, and parietalis 06/10/2023 FKA/UGMS/MSPC 231 37  PART B 06/10/2023 FKA/UGMS/MSPC 231 38  39 EMBRYONIC ORIGIN OF TISSUES, AND DIFFERENTIATION 2023 MSPC 231 Frederick K. Addai, Ph.D. FWACM Department of Anatomy UGMS, Korle-Bu fka/ugms/MSPC 231 06/10/2023  40 PRE-REQUISITE KNOWLEDGE Fertilization – results in the The transition from the restoration of diploidy (2N) MORULA to the BLASTOCYST from haploid (1N) gametes in early development The cell cycle – how cells proliferate by mitosis fka/ugms/MSPC 231 06/10/2023  41 STUDENTS’ LEARNING OUTCOMES (1) 1. The ZYGOTE as the source of all At the end of the (approx. 17 trillion) cells in the body lecture, you 2. Differentiation as a “one-way street” process by which identical cells acquire should be able different characteristics & functions 3. Differentiation is achieved by switching to understand on specific genes, whilst switching off others the following. 4. The concept of POTENCY of cells 06/10/2023  STUDENT LEARNING OUTCOMES (2) 42 5. How cells form TISSUES as a result of DIFFERENTIATION At the end of 6. The embryonic origin of each of the FOUR BASIC the lecture, you TISSUES in the human body should be able 7. The concept of UNDIFFERENTIATED (reserve) cells in most tissues, which resume the cell cycle to to understand replace damaged or senescent (aged) cells the following. 8. Differences in the REGENERATIVE capacity of various TISSUES 06/10/2023  43 CELLS VS TISSUES All cells in the body arise from the zygote TISSUE – is a group of closely associated cells with a similar structure that collectively perform a specific function 06/10/2023  44 CELL DIFFERENTIATION Process by which cells with the same genetic composition acquire different features of shape and other characteristics Hence cells change from one type to another Achieved principally by the in-built ability for cells to respond to different signaling molecules or respond differently to the same molecules 06/10/2023  GENE EXPRESSION REGULATES CELL DIFFERENTIATION Two related processes – 1. Acquisition of unique characteristics, and 2. Loss of capacity to express some other characteristics 45 06/10/2023  GENE EXPRESSION REGULATES CELL DIFFERENTIATION Differentiation is driven by gene expression - Gene expression is the specific combination of genes that are turned on or off (expressed or repressed), and This is what dictates how a cell functions 46 06/10/2023  CELL DIFFERENTIATION IS THE BASIS FOR TISSUE FORMATION 47 06/10/2023 POTENCY OF CELLS 48 06/10/2023 BLASTOCYST AS THE FIRST STAGE OF OBVIOUS CELLULAR DIFFERENTIATION 49 06/10/2023  50 EMBRYONIC ORIGIN OF THE FOUR BASIC TISSUES 1. Epithelia arise from all three primary germ layers – Ectoderm –skin Mesoderm –endothelium Endoderm epithelium of respiratory and gastrointestinal tracts, and urinary bladder 2. Connective Tissues arise exclusively from mesoderm 3. Nerve Tissue arises exclusively from ectoderm 4. Muscle Tissue arises exclusively from mesoderm 06/10/2023  EPIBLAST IS THE ORIGIN OF THE 3 PRIMARY GERM LAYERS VIA THE PRIMITIVE STREAK During gastrulation, cells migrate from the primitive streak which arises from the epiblast to form Endoderm, Mesoderm, and the non-primitive streak epiblast cells that remain form Ectoderm 51 06/10/2023 ORIGIN OF THE PRIMITIVE STREAK 52 06/10/2023  53 CONNECTIVE TISSUE IS THE MOST DIVERSE TISSUE DIFFERENTIATING VIA MESENCHYME fka/ugms/MSPC 231 06/10/2023 FOUR BASIC TISSUES & THREE PRIMARY GERM LAYERS 1. EPITHELIA – Arise from ALL 3 germ layers 2. CONNECTIVE TISSUE - Arise exclusively from MESODERM 3. MUSCLE TISSUE – Arise exclusively from MESODERM 4. NERVE TISSUE – Neurons arise from ECTODERM 54 06/10/2023  POTENCY OF CELLS Refers to the varying ability of stem cells to differentiate into specialized cell types. 55 06/10/2023  POTENCY OF CELLS Cells with the greatest potency can generate more cells types than those with lower potency 56 06/10/2023 Totipotent vs Pluripotent vs Multipotent Comparison Chart 57 06/10/2023  58 fka/ugms/MSPC 231 06/10/2023 HIERARCHY OF CELL POTENCY 1. Totipotent Stem Cells Stem cells that can give rise to any of the 220 cell types found in an embryo as well as extra-embryonic cells (placenta). 2. Pluripotent Stem Cells Stem cells that can give rise to all cell types of the body (but not the placenta). 3. Multipotent Stem Cells Stem cells that can develop into a limited number of cell types in a particular lineage 59 06/10/2023 OLIGOPOTENT STEM CELLS Examples of oligopotent stem cells are the lymphoid or myeloid stem cells. A lymphoid cell specifically, can give rise to various blood cells such as B and T cells, however, not to a different blood cell type like a red blood cell 60 06/10/2023  UNIPOTENT STEM CELLS Unipotent cells can produce Such Unipotent cells only one cell type, their include muscle stem own, but (undifferentiated) cells They have the property of self-renewal, which Most epithelial tissues self- distinguishes them from renew throughout adult life due to the presence of non-stem cells unipotent progenitor cells 61 06/10/2023  LOWEST POTENCY CELLS Unipotent stem cells give rise to cells of their own type along a single lineage. Spermatogonia Hence unipotent stem cells have the lowest differentiation potential compared to other types of stem cells. Skin cells (keratinocytes) are a good example of unipotent stem cells fka/ugms/MSPC 231 62 06/10/2023  CAN CELL DIFFERENTIATION OR POTENCY BE REVERSED? ▪ Artificially shown possible by Somatic Cell Nuclear Transfer (SCNT) ▪ Also called Embryo cloning ▪ Nucleus of unipotent stem cell injected into anucleated mature ovum removed before ovulation ▪ Artificial zygote inseminated into an appropriate female developed into a lamp that was delivered naturally by its surrogate mother Dolly the sheep was first cloned ▪ Grew and reproduced by natural mating mammal from unipotent adult cells in 1996 by Ian Wilmot of Scotland 63 06/10/2023  THE END HAVE A GREAT WEEKEND! 06/10/2023 FKA/UGMS/MSPC 231 64