fertilization fertilization activates the egg activation of the egg triggers embryonic development
TRANSCRIPT
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:– 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:
– Anterior posterior axis, left right sides– After late cleavage polarities form in humans
• Fate maps:– Vital dyes revealed location of blastula cells in e
mbryo
• 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
http://www.uoguelph.ca/zoology/devobio/210labs/24hrwm.htm
24 Hour Chick Embryo
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.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.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