1. Animal Development

2. LE 47-1
1 mm

4. Morphogenesis process by which an animal takes shape
determined by genome and differences between embryonic cells

5. The Acrosomal Reaction
Triggered when sperm reaches egg
releases hydrolytic enzymes that digest material surrounding the egg

6. LE 47-3 Contact and fusion of sperm and egg membranes Entry of sperm
nucleus
Acrosomal
reaction
Sperm plasma
membrane
Sperm
nucleus
Cortical reaction
Contact
Acrosomal
process
Basal body
(centriole)
Sperm
head
Fertilization
envelope
Fused plasma
membranes
Cortical
granule
Actin
Acrosome
Hydrolytic enzymes
Perivitelline
space
Jelly coat
Vitelline layer
Cortical granule
membrane
Sperm-binding
receptors
Egg plasma
membrane
EGG CYTOPLASM

7. The Cortical Reaction Initiated by the fusion of egg and sperm
induces a rise in Ca2+
stimulates cortical granules to release their contents outside the egg
cause formation of a fertilization envelope
block to polyspermy

8. LE 47-4 500 µm 1 sec before fertilization 10 sec after fertilization
Spreading wave
of calcium ions
Point of
sperm
entry

9. Activation of the Egg sharp rise in Ca2+
increases the rates of cellular respiration and protein synthesis by the egg cell
= activation of egg cell

10. Urchin Egg Cell 1 Binding of sperm to egg 2
Acrosomal reaction: plasma membrane
depolarization (fast block to polyspermy) 3 4 6
Seconds 8 10
Increased intracellular calcium level 20
Cortical reaction begins (slow block to polyspermy) 30 40 50 1
Formation of fertilization envelope complete 2
Increased intracellular pH 3 4 5
Increased protein synthesis
Minutes 10 20
Fusion of egg and sperm nuclei complete 30 40
Onset of DNA synthesis 60 90
First cell division

11. Fertilization in Mammals
the cortical reaction modifies the zona pellucida as a slow block to polyspermy

12. LE 47-6
Follicle
cell
Sperm
basal
body
Zona
pellucida
Cortical
ganules
Sperm
nucleus
Egg plasma
membrane
Acrosomal
vesicle
EGG CYTOPLASM

13. Cleavage a period of rapid cell division without growth
partitions the cytoplasm of one large cell into many smaller cells
blastomeres

14. LE 47-7
Fertilized egg
Four-cell stage
Morula
Blastula

15. Polarity eggs and zygotes of many animals (except mammals) Animal pole
Vegetal pole
Most of yolk

16. LE 47-8
Animal
hemisphere
Point of
sperm entry
Animal pole
Vegetal
hemisphere
Vegetal pole
Point of
sperm
entry
Future
dorsal
side of
tadpole
Anterior
Gray
crescent
Right
First
cleavage
Ventral
Dorsal
Left
Posterior
Body axes
Establishing the axes

17. Cleavage planes
follow a pattern relative to the zygote’s animal and vegetal poles

18. LE 47-9 Zygote 0.25 mm 2-cell stage forming 4-cell stage forming
Eight-cell stage (viewed
from the animal pole)
8-cell
stage
0.25 mm
Animal pole
Blasto-
coel
Blastula
(cross
section)
Vegetal pole
Blastula (at least 128 cells)

19. Meroblastic cleavage incomplete division of the egg
occurs in species with yolk-rich eggs
Ie. reptiles and birds

20. LE 47-10 Disk of cytoplasm Fertilized egg Zygote Four-cell stage
Blastoderm
Cutaway view of
the blastoderm
Blastocoel
BLASTODERM
YOLK MASS
Epiblast
Hypoblast

21. Holoblastic cleavage complete division of the egg
occurs in species whose eggs have little or moderate amounts of yolk
Ie. sea urchins and frogs

22. Gastrulation
rearranges the cells of a blastula into a three-layered embryo
a gastrula
has a primitive gut

23. Video: Sea Urchin Embryonic Development
The three layers produced by gastrulation are called embryonic germ layers
The ectoderm forms the outer layer
The endoderm lines the digestive tract
The mesoderm partly fills the space between the endoderm and ectoderm
Video: Sea Urchin Embryonic Development

24. Urchin Key Future ectoderm Future mesoderm Future endoderm Animal pole
Blastocoel
Mesenchyme
cells
Vegetal
plate
Vegetal
pole
Blastocoel
Filopodia
pulling
archenteron
tip
Archenteron
Mesenchyme
cells
Blastopore
50 µm
Blastocoel
Ectoderm
Archenteron
Blastopore
Mouth
Mesenchume
(mesoderm
forms future
skeleton)
Digestive tube (endoderm)
Anus (from blastopore)

25. Frog SURFACE VIEW CROSS SECTION Animal pole Blastocoel Dorsal tip of
blastopore
Dorsal lip
of blastopore
Vegetal pole
Blastula
Blastocoel
shrinking
Archenteron
Ectoderm
Mesoderm
Blastocoel
remnant
Endoderm
Key
Future ectoderm
Future mesoderm
Yolk plug
Yolk plug
Future endoderm
Gastrula

26. Video: Frog Embryo Development
Organogenesis
regions of the germ layers develop into rudimentary organs
the notochord forms from mesoderm
the neural plate forms from ectoderm
curves inward, forming the neural tube
Video: Frog Embryo Development

27. LE 47-14a Neural folds LM 1 mm Neural fold Neural plate Notochord
Ectoderm
Mesoderm
Endoderm
Archenteron
Neural plate formation

28. LE 47-14b Neural fold Neural plate Neural crest Outer layer
of ectoderm
Neural crest
Neural tube
Formation of the neural tube

29. Somites Coelom blocks Formed from mesoderm lateral to the notochord
Lateral to the somites
mesoderm splits to form the coelom

30. LE 47-14c Eye Somites Tail bud SEM Neural tube 1 mm Notochord Neural
crest
Coelom
Somite
Archenteron
(digestive cavity)
Somites

31. LE 47-15 Eye Neural tube Notochord Forebrain Somite Coelom Heart
Archenteron
Endoderm
Lateral fold
Mesoderm
Blood
vessels
Ectoderm
Somites
Yolk stalk
YOLK
Yolk sac
Form extraembryonic
membranes
Neural tube
Early organogenesis
Late organogenesis

33. Adaptations of Amniotes
develop in a fluid-filled sac in a shell or the uterus
Birds
Reptiles
mammals
Germ layers give rise to membranes surrounding embryos

34. Amnion Allantois Embryo Amniotic cavity with amniotic fluid Albumen
LE 47-17
Amnion
Allantois
Embryo
Amniotic
cavity
with
amniotic
fluid
Albumen
Shell
Yolk
(nutrients)
Chorion
Yolk sac

35. Mammalian Development
eggs of placental mammals
Small
store few nutrients
Exhibit holoblastic cleavage
Show no obvious polarity
Gastrulation and organogenesis similar to birds and reptiles
Early cleavage is relatively slow

36. Cleavage forms the blastocyst forms
trophoblast, the outer epithelium of the blastocyst, initiates implantation in the uterus, and the blastocyst forms a flat disk of cells
As implantation is completed, gastrulation begins
The extraembryonic membranes begin to form
By the end of gastrulation, the embryonic germ layers have formed

37. Endometrium (uterine lining) Inner cell mass Trophoblast Blastocoel
LE 47-18a
Endometrium
(uterine lining)
Inner cell mass
Trophoblast
Blastocoel
Blastocyst
reaches uterus.
Expanding
region of
trophoblast
Maternal
blood
vessel
Epiblast
Hypoblast
Trophoblast
Blastocyst
implants.

38. LE 47-18b Expanding region of trophoblast Amniotic cavity Amnion
Epiblast
Hypoblast
Chorion (from
trophoblast
Yolk sac (from
hypoblast)
Extraembryonic
membranes start
to form and
gastrulation
begins.
Extraembryonic mesoderm cells
(from epiblast)
Allantois
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
Yolk sac
Extraembryonic
mesoderm
Gastrulation has produced a
three-layered embryo with four
extraembryonic membranes.

39. Fate Maps
general territorial diagrams of embryonic development

40. Fate map of a frog embryo
LE 47-23a
Epidermis
Central
nervous
system
Epidermis
Notochord
Mesoderm
Endoderm
Neural tube stage
(transverse section)
Blastula
Fate map of a frog embryo

41. Development
Differentiation
Signal molecules
Influence gene

42. Anterior AER Limb bud ZPA Posterior Apical ectodermal ridge 50 µm
LE 47-26a
Anterior
AER
Limb bud
ZPA
Posterior
Apical
ectodermal
ridge
50 µm
Organizer regions