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