BIOL131 Chp43 Cleavage 2024 PDF

The most important event in your life? 43 Define the term ‘gastrulation’. Be able to name the 3Loading… germ layers formed during gastrulation; also know the final main tissues or organs that each layer eventually becomes. Gastrulation: the process by which the three germ layers of the animal embryo...

The most important event in your life? 43 Define the term ‘gastrulation’. Be able to name the 3Loading… germ layers formed during gastrulation; also know the final main tissues or organs that each layer eventually becomes. Gastrulation: the process by which the three germ layers of the animal embryo are formed: ectoderm, mesoderm, and endoderm. Ectoderm – Outer layer (skin/nervous system) Mesoderm – Middle layer (muscles and organs) Endoderm – innermost layer digestive and respiratory tract. Gastrulation in animal embryos. Blastulation Sea urchin Frog Chick Gastrulation √ Loading… √ √ 43 Be familiar with the process of gastrulation in the in the sea urchin (know the major structures including: mesenchyme cells, blastopore, Archenteron, skeletal rods and stomodeum. Sea urchin gastrulation Part 1 Blastula Primary mesenchyme enter blastocoel Vegetal Hemisphere Flattens The movement of primary mesenchyme cells (descendents of the micromeres) to the interior of the sea urchin blastula. This occurs at the vegetal plate. Primary mesenchyme cells dissociate from neighboring cells, begin to move out and in the process secrete enzymes to degrade extracellular matrix Sea urchin gastrulation Pt. 2 Blastopore Mouth Anu s SEM of broken sea urchin, showing the primary mesenchyme cells inside the blastocoel. Loading… Sea urchin blastopore, SEM Sea urchin gastrula, showing the archenteron Ectoderm Blastopore Archenteron Sea urchin pluteus (Larval Stage) Early development of sea urchin embryo, from blastula to larval stage. Gastrulation: the process by which the three layers of the embryo are formed: ectoderm, mesoderm, and endoderm. Sea urchin √ Frog Chick 43 Know how to describe the process of gastrulation in the frog. How do the bottle cells contribute to this process? What structure contributes to the formation of the ventral lip? Frog Blastula Cell Fate Map I thought I was never going to gastrulate Gastrulation in the frog embryo Gastrulation begins when bottle cells in the region of the gray crescent move inward, forming the dorsal lip of the future blastopore. Bottle cells Developing archenteron Cells moving toward animal pole Blastopore Cells of the animal pole spread out, pushing surface cells below them toward and across the dorsal lip. These cells involute into the interior of the embryo, where they form the endoderm and mesoderm. Involution creates the archenteron and destroys the blastocoel. The blastopore lip forms a circle, with cells moving to the interior all around the blastopore; the yolk plug is visible through the blastopore. The development of the frog blastopore. As in the sea urchin, the blastopore becomes the anal end of the gut. Gastrulation: the process by which the three layers of the embryo are formed: ectoderm, mesoderm, and endoderm. Sea urchin √ Frog √ Chick Summary of blastula formation in the oviduct of the hen 43 Be familiar with the process of gastrulation in the in the chick embryo (know the contributions of the primitive streak, Henson’s node, primitive groove). How do the 3 main layers arise from the epiblast? What does the hypoblast contribute? Diagram of chick blastula formation Primitive Streak Formation in the Chick View of blastodisc from dorsal side. Posterior epiblast cells change shape and thicken, forming the primitive streak. Cells migrate, converging at the primitive streak and causing it to elongate. Primitive Streak Primitive Streak Formation in the Chick The primitive groove (Chick Blastopore) (Cells ingress here) The chick primitive streak at its full extent Consider a crosssection through here Loading… Hensen’s node The depressed area at the center of the primitive streak is called the primitive groove All three parts of the embryo, ectoderm, mesoderm and endoderm, are formed from the epiblast. The hypoblast only serves as a support, and is displaced by migrating endoderm cells from the epiblast. Gastrulation in the chick The primitive groove is an elongated blastopore. 43 Neural Development (Development of the Brain, Spinal Cord and Peripheral nerves) Life after gastrulation; The post-gastrulation development of vertebrates Do you believe in fate? Blastula Gastrula Endoderm Ectoderm Mesoderm Loading… Notochord Ectoderm fate map 43 Understand the term – primary Loading… induction. The development and function of the vertebrate nervous system A major function of gastrulation of vertebrates is to bring mesoderm underneath the ectoderm on the dorsal side of the embryo, and then to form a notochord. The notochord then sends a signal to the ectoderm, and causes it to form a neural plate. This is called primary induction. Cut a section through here 43 Be able to explain the major steps involved in neurulation; include the role of the neural plate, neural tube, notochord, neural crest cells and somites. Stages in the process of neurulation in amphibian embryos Notochord This diagram summarizes the formation of the neural tube and crest cells from the neural ectoderm. The neural tube will become the brain and spinal chord; the neural crest cells will become the peripheral nerves A similar process occurs in all vertebrate embryos. Neurulation in the chick Notochord not seen here, but indicated as blue circle Neurulation in the chick Loading… Two possibilities for the mechanism of primary induction. Release of Positive Factors In one (A), the signal from the notorchord instructs the overlying epithelium to become neural. Release of Negative Factors In the other (B), the signal overrides instruction to become epidermal, allowing the default pathway of neural development to proceed. Two possibilities for the mechanism of primary induction. Release of Positive Factors !! In one (A), the signal from the notorchord instructs the overlying epithelium to become neural. Development of the neural tube The later patterning of the neural tube depends on further signals from the notochord and from the ectoderm. This sets up gradients of proteins and cells “read” their position in the gradients and respond accordingly. 43 Know how the notochord contributes to the formation and continued development of the neural tube. How are the molecules Shh, TGF and BMP involved in this process? What type of protein is Shh? What are the major types of neurons that initially develop from the neural tube? Sonic hedgehog (Shh) is produced by the notochord. BMP BMP Transforming growth factor (TGF) BMP Motor neurons The release of Shh from the notochord and BMP from the ectoderm leads to gradients of growth factors in the developing neural tube. Cells within the neural tube read their positions within the gradients and differentiate accordingly. Blue marks a protein induced by a signal from the ectoderm. Sonic hedgehog (Shh, stained green) in the notochord and floor plate of the neural tube. Motor neurons are seen in orange/yellow. Sonic hedgehog (Shh) is a protein secreted from notochord cells that activates a receptor in neural tube cells and directs motor neuron formation. Landmark Features of the Developing Neurula Consider the ectoderm origins of the neural crest cells. Notochord Neural Crest cells go on to form the peripheral nerves. Lateral SEM view of the neural tube and notochord of frog embryo, showing the neural crest cells migrating off of the neural tube Somites are bilaterally paired blocks of mesoderm that form along the head-to-tail axis of the developing embryo in segmented animals. Somites eventually differentiate into skeletal muscle, cartilage, and tendons. Neural crest cells migrate from the dorsal side of the neural tube and travel throughout the developing embryo. The migration begins at the anterior end of the neural tube with the more posterior neural crest cells migrating later. Neural Crest Cells lead to the formation of Melanocytes, Cranial Nerves and Ganglia Ganglia are cluster of nerve cells found outside the spinal chord the serve as information relay structures to and from the central nervous system Migration of Neural Crest Cells at the forebrain and hindbrain Section through forebrain The further development of the brain and spinal cord. 43 Be able to convey how the neural tube results in the formation of the brain. The anterior portion of the Neural tube forms the Brain while the posterior portion forms the spinal cord Section through forebrain Loading… The vertebrate brain develops at the anterior end of the neural tube. Initially, three vesicles of the neural tube are the Forebrain, Midbrain and Hindbrain. The forebrain controls BT, reproductive functions, eating, sleeping, emotions. The midbrain controls vision, hearing, motor control. Hindbrain develops into medulla, pons and cerebellum and supports vital autonomic processes. Cross section of Forebrain Area Cross section of Midbrain Area Cross section of Hindbrain Area