1. Fertilization Fertilization activates the egg
Activation of the egg triggers embryonic development

2. 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

3. 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

4. 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

5. 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

6. Stages of Early Development
Cleavage leads to multicellular blastula
Gastrulation leads to three tissue layered gastrula
Organogenesis generates rudimentary organs

7. 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

8. Gastrulation Sea urchins Frogs
Rearrangement of cells leads to 3 germ layers
Ectoderm
Nervous system
Outer skin layer
Eyes

9. Endoderm: Mesoderm: Lines archenteron Liver Pancreas Lining of urethra
Reproductive system
Mesoderm:
Kidneys
Muscles
Heart and circulatory system
Excretory system
Notochord and skeletal system

10. 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

11. 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

12. 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
                                                                                

15. Mammalian Development
Holoblastic cleavage
Inner cell mass becomes embryo

16. 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

17. 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

21. Gray crescent is an early polarity marker

50. 24 Hour Chick Embryo

51. 33 Hour Chick Embryo

52. 48 Hour Chick Embryo

54. 72 Hour Chick Embryo

55. http://www. bioscience. drexel

57. http://www. bioscience. drexel

63. Changes in shape and position lead to elongation and direction of movement