Download How is the acrosomal reaction species specific?

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
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.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