CHAPTER 23 Animal Development PPT Notes development proceeds in ordered phases in an animal life cycle 1 fertilization 2 cleavage 3 gastrulation 4 organogenesis fertilization sperm fertilize egg steps 4 25 2014 1 chemoattraction of sperm to egg 2 binding to jelly layer 3 acrosome rxn sperm s enzymes dissolve outer egg coverings 4 flagellar hyperactivity 5 penetration of egg 6 egg sperm membrane 7 entry of sperm nucleus coats fusion into egg o o o o o o o sea urchins model that produce large s of gametes undergo external fertilization bindin protein on sea urchin sperm head that binds to surface of eggs only binds to eggs of same species polyspermy fertilization by more than 1 sperm sea urchins prevent by creation of physical barrier after fertilization o Ca2 based signal induced propagated through egg forms fertilization envelope barrier in mammals cortical granules release enzymes that modify egg cell receptors prevent binding by additional sperm cleavage rapid cell divisions in animal zygotes immediately after fertilization occurs in mammals before uterus implantation first step in embryogenesis makes a single celled zygote into multicellular embryo partitions egg cytoplasm w o growth of zygote blastomeres cells made by cleavage divisions blastula mass of blastomere cells after cleavage is complete gastrulation extensive highly organized cell movements rearrange embryonic cells into gastrula structure results in formation of embryonic tissue layers tissue integrated set of cells that function as a unit early embryos have 3 primary tissue layers aka germ layers give rise to adult tissue organs ectoderm mesoderm endoderm o ectoderm forms outer covering of adult body nervous system nervous system cornea eye lens epidermis epithelial lining of mouth rectum o mesoderm forms muscle most internal organs connective tissues bone cartilage skeletal circulatory lymphatic muscular excretory reproductive system dermis lining of body cavity o endoderm forms digestive tract lining some associated organs epithelial lining of digestive respiratory reproductive urinary tracts liver pancreas thyroid parathyroids thymus o end of gastrulation 3 embryonic tissues arranged in layers gut formed IMPT major body axes visible organogenesis process of tissue organ formation o begins when gastrulation is complete embryonic germ layers are in place 4 25 2014 o o cells proliferate become differentiated notochord forms early in organogenesis in dorsal mesoderm unique to animal group chordates key organizing element in organogenesis as organogenesis continues notochord cells undergo apoptosis signals trigger reorganization of dorsal ectodermal cells forms neural tube neural tube precursor to brain spinal cord notochord forms notochord signals ectoderm to fold neural tube formation complete somites form somites mesodermal cells organized into blocks of tissues form on both sides of neutral tube o o o form a variety of structures but are initially not determined as they mature become irreversibly determined differentiate into specific cell type based on location within somite determination process through which somite cells differentiate in response to signals from nearby tissues signals diffuse away from cells in notochord neural tube nearby ectoderm and mesoderm to act on specific populations of target cells in somite muscle cell differentiation o cell differentiation overview differentiation is step by step process completed when cells begin making cell specific proteins 1 fertilization triggers cleavage blastocyst 2 blastocyst cell signals trigger gene cascades positional changes during gastrulation 3 organogenesis notochord signals specific somite cells to begin MyoD proctuion targeting specific cells as belonging to specific muscles MyoD protein that causes muscle cell differentiation regulatory transcription factor that binds to enhancers upstream of muscle specific nucleus o myoblast cell determined to become muscle cell but has not begun producing muscle specific proteins 4 25 2014 CHAPTER 23 Animal Development Blue Thread Questions If you understand the importance of protein protein interactions for binding sperm and egg you should be able to explain why adding a molecule that bound to a bindin like protein on the human sperm head would be an effective contraceptive Predict the consequences of mutations that change the structure of bindin of sea urchin species A to the bindin structure of sea urchin species B Describe the role of calcium signaling in processes that block polyspermy Explain what would happen if cytoplasmic determinants were not localized in specific parts of the egg Predict which germ layers would be present in an animal that during development uses only two germ layers State when you would first be able to point out the future anterior and ventral portion of the embryo and explain what clues you would use to identify their positions Predict how the formation of the neural tube would be affected by a drug that locks the cytoskeleton in place What causes cells in a certain part of somites to become committed to produce muscles Predict how the formation of the neural tube would be affected by a drug that locks the cytoskeleton in place You should be able to explain why bindin and the egg cell receptor for sperm are said to interact like a lock and key You should be able to describe how cleavage in a frog embryo can result in certain cells containing a cytoplasmic determinant You should be able to compare and contrast in broad terms a mesodermal cell in the anterior end of an embryo and a mesodermal cell in the posterior end regarding the cell cell signals they receive and the regulatory transcription factors they contain You should be able to give examples of cell cell signals expansion movement proliferation and differentiation during neural tube somite and muscle development in mammals 4 25 2014 4 25 2014
View Full Document
Unlocking...