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

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

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

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• 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• 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

FrogChick

When the three germ layers begin to develop into organs

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

USTHEM

(chicken)

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