Animal Development

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Primary structures: Neural tube

Dorsal lip of blastopore

Secondary (induced) embryo

Notochord

Pigmented gastrula (donor embryo)

EXPERIMENT

Primary embryo

RESULTS

Nonpigmented gastrula (recipient embryo)

Secondary structures: Notochord (pigmented cells)

Neural tube (mostly nonpigmented cells)

Slide 57

Formation of the Vertebrate Limb

Inductive signals play a major role in pattern formation, development of spatial organization.

The molecular cues that control pattern formation are called positional information.

This information tells a cell where it is with respect to the body axes.

It determines how the cell and its descendents respond to future molecular signals.

Slide 58

The wings and legs of chicks, like all vertebrate limbs, begin as bumps of tissue called limb buds.

The embryonic cells in a limb bud respond to positional information indicating location along three axes

Proximal-distal axis

Anterior-posterior axis

Dorsal-ventral axis

Slide 59

Vertebrate limb development

(a) Organizer regions

Apical ectodermal ridge (AER)

Digits

Limb buds

(b) Wing of chick embryo

Posterior

Anterior

Limb bud

AER

ZPA

50 µm

Anterior

2

3

4

Posterior

Ventral

Distal

Dorsal

Proximal

Slide 60

Signal molecules produced by inducing cells influence gene expression in cells receiving them.

Signal molecules lead to differentiation and the development of particular structures.

Hox genes also play roles during limb pattern formation.

Slide 61

Review

Sperm-egg fusion and

depolarization of egg membrane (fast block to polyspermy)

Cortical granule release (cortical reaction)

Formation of fertilization envelope (slow block to polyspermy)

Slide 62

Review: Cleavage frog embryo

Blastocoel

Animal pole

2-cell stage forming

8-cell stage

Blastula

Vegetal pole:

yolk

Slide 63

Review: Gastrulation / Early Embryonic Development

Sea urchin

Frog

Chick/bird

Slide 64

Review: Early Organogenesis

Neural tube

Coelom

Notochord

Coelom

Notochord

Neural tube

Slide 65