Animal Development
Emily Huang, Erin McGrath,
Michelle Xu
Review
• Cell differentiation
• Morphogenesis
• Blastula
• Gastrulation
• Cytoplasmic
determinants
Fertilization
• Sperm + egg  combine to form diploid
(zygote)
– Contact of sperm to surface of egg initiates
metabolic reactions within egg that trigger onset
of embryonic development
• Acrosomal Reaction
• Cortical Reaction
Fertilization In Different Species
Similarities
-contact, acrosomal reaction (dig hole into egg), fusion of sperm and egg
membranes, complete entry of sperm, cortical reaction blocks other sperm
from coming in
-sperm cell contains basal body which becomes the centrosome and allows
zygote to split
Differences
Mammal
-internal fertilization
-eggs coated in follicle cells
-fusion doesn’t not occur until
after first cell division (12-36
hours)
Echinoderm
-external fertilization
-eggs have a jelly coat
-nuclei of sperm and egg fuse
immediately
-first cell division occurs 90
minutes after fusion
After Fertilization…
• …embryonic development proceeds through
cleavage, gastrulation, and organogenesis.
– Stage 1: cleavage  cell division creates a hollow
ball of cells (blastula) from the zygote
– Stage 2: gastrulation  produces 3 layered
embryo (gastrula)
– Stage 3: organogenesis  generates rudimentary
organs from which adult structures grow
Cleavage
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Blastomeres: smaller cells that result from cleavage, each with its own nucleus
First 5-7 divisions form a cluster of cells known as the morula
Blastocoel: fluid filled cavity that begins to form within the morula
Yolk: stored nutrients, most concentrated toward one pole, the vegetal pole
and decreases toward the animal pole
Afterwards, gastrulation occurs
Gastrulation
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Dramatic rearrangement!
Forms primitive gut
Driven by changes in cell motility, cell shape, and cellular adhesion to other cells and e.c. matrices
3 layers produced- collectively the gastrula
Germ layers: ecto, meso, endo
Sea Urchins:
Frogs:
Chicks:
Germ Layer Fun
ECTODERM:
-skin (sweat glands,
hair follicles)
-sensory receptors in
epidermis
-cornea, lens of eye
-nervous system
-tooth enamel
MESODERM:
-skeletal system
-muscular system
-excretory system
-circulatory and
lymphatic systems
-reproductive
system
-dermis of skin
ENDODERM:
-epithelial lining of
digestive tract and
respiratory system
-lining of urethra,
urinary bladder,
repro. system
-liver, pancreas,
thymus, thyroid
Organogenesis
When the three germ layers begin to
develop into organs
Frog
Chick
Development Adaptations of Amniotes
• Reptiles, birds, and mammals are called
amniotes.
• All vertebrate embryos require aqueous
environment, so animals use fluid filled eggs
or uteri
Extraembryonic Membrane
• Present in mammals, birds and reptiles.
• In birds and reptiles: germ layers develop into
– Amnion- contains the fluid and fetus
– Yolk sac, chorion, and allantois
• Allantois is a disposal sac for waste
• Yolk sac expands over yolk, stockpile of nutrients
• Exchange gases between embryo and surroundings
• These structures provide “life support system”
• Mammals have the same structures, only we
have a uterus instead of an egg to contain them
THEM
(chicken)
US
Morphogenesis
• Cytoskeletons in animals cells allow them to “crawl”
from place to place in all developing animals.
• Cell crawling changes the shape of the developing
animal by extending or contracting- convergent
extension
What affects developmental fate?
• Cytoplasmic determinants  cell differentiation
• Interactions among cells causes changes in gene
expression  “induction”
Limb Formation and
Spatial Organization
• Inductive signals play a major
role in pattern formation
• Positional information:
molecules that direct a cell to
its correct location in the body
• In all animals with limbs: apical
ectodermal ridge (AER), zone of
polarizing activity (ZPA)
• They are major limb bud
organizers
• apical ectodermal ridge (AER)- a thick ridge of
ectoderm at the tip of a bud of a limb,
determines growth of the limb
• zone of polarizing activity (ZPA)- sprouts from
the mesoderm, forms the digits
• ZPA excretes a protein growth factor
called SONIC HEDGEHOG!!!!!!!!!!!!!!
• THE END <3