Animal Development

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This mechanism is called induction, and is mediated by diffusible chemicals or cell-cell interactions.

Slide 50

Fate maps are general territorial diagrams of embryonic development.

Classic studies using frogs indicated that cell lineage in germ layers is traceable to blastula cells.

To understand how embryonic cells acquire their fates, think about how basic axes of the embryo are established.

Slide 51

Fate Mapping for two chordates

Epidermis

(b) Cell lineage analysis in a tunicate

(a) Fate map of a frog embryo

Epidermis

Blastula

Neural tube stage (transverse section)

Central nervous system

Notochord

Mesoderm

Endoderm

64-cell embryos

Larvae

Blastomeres injected with dye

Slide 52

The Axes of the Basic Body Plan

In nonamniotic vertebrates, basic instructions for establishing the body axes are set down early during oogenesis, or fertilization.

In amniotes, local environmental differences play the major role in establishing initial differences between cells and the body axes.

In many species that have cytoplasmic determinants, only the zygote is totipotent.

That is, only the zygote can develop into all the cell types in the adult.

Slide 53

Unevenly distributed cytoplasmic determinants in the egg cell help establish the body axes.

These determinants set up differences in blastomeres resulting from cleavage.

As embryonic development proceeds, potency of cells becomes more limited.

After embryonic cell division creates cells that differ from each other, the cells begin to influence each other’s fates by induction signals.

Slide 54

How does distribution of the gray crescent affect the development potential of the two daughter cells?

Thread

Gray crescent

Experimental egg (side view)

Gray crescent

Control egg (dorsal view)

EXPERIMENT

Normal

Belly piece

Normal

RESULTS

Slide 55

The Dorsal Lip = “Organizer” of Spemann and Mangold

Based on their famous experiment, Hans Spemann and Hilde Mangold concluded that the blastopore’s dorsal lip is an organizer of the embryo.

The Spemann organizer initiates inductions that result in formation of the notochord, neural tube, and other organs.

Slide 56

Can the dorsal lip of the blastopore induce cells in another part of the amphibian embryo to change their developmental fate?