Animal Development Chapter 47

Slide 2 of 13 Post-fertilization  After fertilization, embryology occurs  Embryology is the development of the zygote  Focus on the development of mammalian embryos

Slide 3 of 13 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

Slide 4 of 13 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?

Slide 5 of 13 Notes on Fertilization (page 2)  Cortical reaction  Fusion of gametes results in release of Ca 2+ 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  Ca 2+ ion release also causes activation of the egg/zygote to undergo an ontogenic process

Slide 6 of 13 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

Slide 7 of 13 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

Slide 8 of 13

Slide 9 of 13

Slide 10 of 13  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

Slide 11 of 13 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

Slide 12 of 13 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

Slide 13 of 13 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?