DEVELOPMENTAL BIOLOGYFertilization to Gastulation

ANIMAL DEVELOPMENT

Embryology - study of development of the Embryo

5 major stages..1. Gametogenesis - gamete production 2. Fertilization - gamete --> zygote3. Cleavage - Zygote --> Blastula4. Gastrulation - Blastula --> Gastrula5. Organogenesis - Organ Formation-i.e. Neurulation- Gastrula --> Neurula

FERTILIZATION

1. Sperm attaches the jelly coat of the egg

Acrosome cap -contains digestive enzymes that

eat away at jelly layer

FERTILIZATION

2. Sperm reach vitelline envelopeVitelline layer-species-specific boundary involved in

sperm-egg recognition

• ensure other species cannot fertilize the egg

FERTILIZATION

3. Sperm /egg plasma membrane fuse

Sperm nucleus enters the egg

Fertilization occurs-sperm nucleus and egg nucleus form a 2N zygote

FERTILIZATION

Prevention of Polyspermy – entrance of multiple sperm 1.Change of electrical potential of the egg plasma membrane- fast 2.Confusion of sperm- Egg releases all of their Ca ions

CLEAVAGE

• Cleavage-rapid succession of cell division • doubling with each division each cell smaller than zygote

•The produced cells named Blastomeres.

During this stage the size of the embryo does not change, the blastomeres become smaller with each division

BLASTULA continues divisions to form a ball of 32 cells called

the morula. The morula continues divisions to form the hollow

blastula with up to several hundred cells. The cavity of the blastula is the blastocoel– fluid

filled cavity forms at the center of embryo

Vegetal Hemisphere -the lower, yolky portion of the egg; opposite the animal hemisphere.

CLEAVAGE OF A FROG

Starfish development, unfertilized egg. 2 blastomeres.

Starfish development, nonmotile

blastula.

4 blastomeres.

16 blastomeres. 32 blastomeres.

morula

GASTRULATION

GASTRULATION (literal meaning - to form a stomach) is a complex series of cell movements

Blastula (hollow ball of cells) transformed into the Gastrula (three layered stage)

GASTULATION

1. rearranges cells, giving them new neighbors (and thus potentially new signals from other cells and the environment)

2. results in the formation of 3 GERM LAYERS that will form the subsequent embryo: ECTODERM, ENDODERM, and MESODERM

GASTRULATION

1. Gastrulation begins- Blastopore formed Blastopore - midway opening on one side of the blastula

• Site of cell migration from the surface into the interior

• Future site of anus (Deuterostome) or mouth (Protostome)

GASTRULATION

2. Cell migrating to form layers

• Archenteron –primitive gut formed (endoderm)

• The open end of the archenteron is called the blastopore

An echinoderm gastrula.

A - ectoderm; B - blastocoel;

C - archenteron; D - endoderm; E - blastopore.

GASTRULATION

3.Gastrulation complete - Gastrula formed:• Endoderm and archenteron -replace the

blastocoel• Mesoderm - forms a layer between the

ectoderm and endoderm• Ectoderm- forms the outer layer except for a

cluster of endodermal cells (yolk plug)• Yolk plug- (endoderm) marks the site of the

blastopore and of the future anus

DEVELOPMENT OF EGG CELLS

4 stages of embryonic development

1.Cleavage (Mitosis and cytokinesis of thezygote, )

2.Patterning (organize themselves in layers and masses)

3.Differentiation

4.Grow

PROTOSTOME

Protostome: animals whose development is characterized by: the mouth is derived from the blastopore

Determinate is the form of cleavage in most protostomes. It results in the developmental fate of the cells being set early in the embryo development.

spiral determinate cleavage

Arthropod

Molluscs

Rotifers

DEUTEROSTOME Deuterostome: animals

whose development is characterized by:

the mouth is not derived from the blastopore

Indeterminate - when the original cell in a deuterostome embryo divides, the two resulting cells can be separated, and each one can individually develop into a whole organism

Echinoderm

Chordates

Hemichordata

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STEM

CELLS

Early in development, a group of cells called the inner cell mass (ICM) forms. These cells are able to produce all the tissues of the body. Later in development, during gastrulation, the three germ layers form, and most cells become more restricted in the types of cells that they can produce

DnaTube.com - Human Development and Stem Cells_WMV V9.wmv

ORGANOGENESIS

Organogenesis is the formation of the organs The layers are germ layers; they have

specific fates in the developing embryo: Endoderm: The innermost lining of digestive

tract, liver, pancreas, lungs

Mesoderm:The middle layer. Goes on to form the blood and muscles, skeleton, gonads, excretory system, circulatory system.

Ectoderm :The outermost. Goes on to form the skin and nervous system

Human reproduction is an inefficient process:

~ 50% of concepti do not implant (implantation 8-10 dpf, Heart beat at 21 dpf).

a further ~30% die and abort after implantation.