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Animal Development

Animal Development. Chapter 47. Post-fertilization. After fertilization, embryology occurs Embryology is the development of the zygote Focus on the development of mammalian embryos.

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Animal Development

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  1. Animal Development Chapter 47

  2. Post-fertilization • After fertilization, embryology occurs • Embryology is the development of the zygote • Focus on the development of mammalian embryos

  3. Acrosomal Reaction – the acrosome on the sperm secretes hydrolytic enzymes to digest the egg’s jelly coat. Acrosomal process – actin filaments that protrude from acrosome & binds to membrane receptors on the egg

  4. Notes on Fertilization • After the acrosomal process binds to membrane receptors, the sperm & egg membranes fuse • Depolarization of the egg membrane occurs preventing other sperm from binding to the egg • Depolarization is due to ion channels opening in the egg membrane, so Na+ ions flow into the egg • Depolarization prevents Polyspermy – more than 1 sperm binding to an egg • Is polyspermy bad?

  5. Notes on Fertilization (page 2) • Cortical reaction • Fusion of gametes results in release of Ca2+ ions from the ER into the space between the jelly coat and plasma membrane • Swelling of the perivitelline space • Hardening of the vitelline layer • Removal of sperm-binding receptors on egg membrane • Collectively the above are called the fertilization envelope • Ca2+ ion release also causes activation of the egg/zygote to undergo an ontogenic process

  6. Ectoderm – Skin, teeth, Nervous system Mesoderm – Skeletal, Muscular, Circulatory, Reproductive Systems (Blood, bones, and muscles) Endoderm – Epithelial linings of the digestive, respiratory, & excretory tract. Liver & Pancreas as well

  7. Continuing Development • Organogenesis • Development of the 3 germ layers into rudimentary organs • Notochord – rigid dorsal rod (cartilage or bone) • Develops from mesoderm • Neural plate – will become brain & spinal cord • Develops from ectoderm • Neurulation • Process of forming dorsal hollow nerve chord

  8. Blastocyst – mammalian version of blastula • Inner cell mass – group of cells that develops into the embryo • Source of embryonic stem cell lines • Trophpblast – outer epithelium of the blastocyst, becomes the fetal portion of placenta

  9. Pattern of Development • Development is governed by a combination of cytoplasmic determinants & inductive cell signals • Cytoplasmic determinants • Chemical signals such as mRNA & transcription factors that were distributed unevenly during cleavage • Induction • Interaction among cells that influence their fate • Causes changes in gene expression among cells

  10. Totipotent Cells • Cells that are capable of developing into ANY possible cell type • As long as it possesses the requisite genetics, it can become muscular, nervous, epithelial, etc. • If you have a totipotent cell, you can literally grow another organism, and you can grow as many as you would like • Totipotent cells exist until the 16-cell stage of cleavage • After that, they are pluripotent – can become any of the 3 germ layers, but cannot develop into a new being

  11. iPS Cells • iPS – Induced pluripotent stem cells • Take an adult (fully differentiated) cell, modify the signaling being received, thus altering the genetic expression of certain “induction” genes • Future of medicine?

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