Fertilization Fertilization activates the egg Activation of the egg triggers embryonic development
Acrosomal Reaction The acrosomal reaction occurs in echinoderms such as sea urchins How is the acrosomal reaction species specific? Receptors on the vitelline egg layer are specific The reaction is the fast block to polyspermy A depolarization of the membrane stops other sperm from penetrating
Cortical Reaction Slow block to polyspermy Signal transduction pathway is triggered by fusion of sperm and egg G protein releases calcium from ER of egg Increase in calcium ions causes cortical granules to fuse with plasma membrane Cortical granules release enzymes that lead to fertilization membrane
Activation of The Egg Increase in calcium also triggers increase in metabolic reaction in the egg Artificial activation of egg can occur by injecting calcium ions
Mammalian Fertilization Most mammals show internal fertilization Capacitation of sperm occurs within the female Sperm has to reach zona pellucida by penetrating follicle cells An acrosomal reaction occurs and sperm cell enters egg Zona pelucida hardens which blocks polyspermy Centrosomes originate from sperm cell Chromosomes share a common spindle during first mitotic division
Stages of Early Development Cleavage leads to multicellular blastula Gastrulation leads to three tissue layered gastrula Organogenesis generates rudimentary organs
Cleavage Fast mitotic divisions without G1 and G2 phases Results in smaller blastomeres Polar planes of division occur with animal and vegetal poles Holoblastic cleavage is complete division of eggs with little yolk Meroblastic = incomplete division
Gastrulation Sea urchins Frogs Rearrangement of cells leads to 3 germ layers Ectoderm Nervous system Outer skin layer Eyes
Endoderm: Mesoderm: Lines archenteron Liver Pancreas Lining of urethra Reproductive system Mesoderm: Kidneys Muscles Heart and circulatory system Excretory system Notochord and skeletal system
Organogenesis Folding, splitting and clustering of cells begins organogenesis Ectoderm rolls into neural tube Mesodermal blocks form somites along axis of notochord: Gives rise to vertebrae and muscles of backbone Neural plate folds into the neural tube and becomes central nervous system
Amniote Embryo Development Vertebrates need watery environment for development Terrestrial animals: evolved shelled egg or uterus for embryonic development Chick development Meroblastic cleavage Primitive streak invaginates during gastrulation
Chorion - gas exchange and waste storage, lines the egg shell Allantois – gas exchange and waste storage connects embryo to chorion Yolk sac – food storage vitelline vessels embed into the yolk Amnion – protective fluid filled sac
http://eng-sci.udmercy.edu/courses/bio123/Chapter49/Chick.html
Mammalian Development Holoblastic cleavage Inner cell mass becomes embryo
Organogenesis Polarity: Fate maps: Determination Anterior posterior axis, left right sides After late cleavage polarities form in humans Fate maps: Vital dyes revealed location of blastula cells in embryo Determination Protostomes only zygote is totipotent Deuterostomes potency restriction is progressive Determined cell fate does not change Involves cytoplasmic control of genome
Cytoplasmic determinants regulate development Morphogenetic movements are changes in cell shape and cell migration Influenced by extracellular matrix Induction: One group of cells influences development of neighboring cells Seen with the organizer (dorsal lip) and lens formation Pattern formation: Arrangement of organs and tissues within 3D space Organizer regions for pattern formation have been isolated
Gray crescent is an early polarity marker
http://www.uoguelph.ca/zoology/devobio/210labs/frogcleavage.htm
http://www.uoguelph.ca/zoology/devobio/210labs/frogcleavage.htm
http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation2.html
http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation2.html
http://academic.regis.edu/tnakamur/FinalPractice/four.htm
http://www.blc.arizona.edu/Marty/181/181Lectures/S02Lecture20.html
http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation2.html
http://www2.sunysuffolk.edu/sabatil/frog-gastrula.htm
http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation2.html
http://www2.sunysuffolk.edu/sabatil/frog-gastrula.htm
http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation2.html
http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation2.html
http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation2.html
http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation2.html
http://www2.sunysuffolk.edu/sabatil/frog/frog-neurula.htm
http://www2.sunysuffolk.edu/sabatil/frog/frog-neurula.htm
http://www2.sunysuffolk.edu/sabatil/frog/frog-neurula.htm
http://www.uoguelph.ca/zoology/devobio/210labs/ntfrog.htm
http://www.uoguelph.ca/zoology/devobio/210labs/ntfrogXS.htm
http://www.uoguelph.ca/zoology/devobio/210labs/ntfrogXS.htm
http://www.uoguelph.ca/zoology/devobio/210labs/ntfrogXS.htm
24 Hour Chick Embryo http://www.uoguelph.ca/zoology/devobio/210labs/24hrwm.htm
33 Hour Chick Embryo http://www.uoguelph.ca/zoology/devobio/210labs/33hrwm.htm
48 Hour Chick Embryo http://www.uoguelph.ca/zoology/devobio/210labs/48hrwm1.htm
72 Hour Chick Embryo http://www.uoguelph.ca/zoology/devobio/210labs/72hrwm.htm
http://www. bioscience. drexel http://www.bioscience.drexel.edu/Homepage/Spring2003/BIO%20268/Embryology/Chick/pages/C6_W006T.htm
http://biology.clc.uc.edu/fankhauser/Labs/Anatomy_&_Physiology/A&P202/Brain_Development/embryo_15x_PC271481md.JPG
http://www. bioscience. drexel http://www.bioscience.drexel.edu/Homepage/Spring2003/BIO%20268/Embryology/Chick/pages/C7_W002T.htm
http://www.uoguelph.ca/zoology/devobio/210labs/24hrwm.htm
Changes in shape and position lead to elongation and direction of movement