Animal Development

Chapter 47

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Post-fertilization

After fertilization, embryology occurs

Embryology is the development of the zygote

Focus on the development of mammalian embryos

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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

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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?

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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

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

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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

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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

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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

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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

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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?