(发育生物学）IV 早期胚胎发育.ppt

Developmental Biology
Chapter 4: Early embryonic development
Early embryonic development
After fertilization, the zygote begins the production of a anism. Between the events of fertilization and events an formation are two critical developmental stages: cleavage (卵裂) and gastrulation (原肠胚形成).
During cleavage, rapid cell divisions divide the cytoplasm of the fertilized egg into numerous cells. These cells then undergo dramatic displacements during gastrulation, a process whereby they move to different parts of the embryo and acquire new neighbors.
During cleavage and gastrulation,
The major axes of the embryo are determined (pattern formation)
Cells begin to acquire their respective fates (cell fate determination)
Early embryonic development
1 Cleavage and formation of the blastula
The main patterns of cleavage
The blastocoel and its function
2 Gastrulation
The concept and ic movements
The cell/tissue movements involved in gastrulation
3 The cell fate specification and determination
The fate map in sea urchin
The Xenopus fate map
Early embryonic development
4 The axis formation
We will discuss this part in next chapter in detail
5 Early embryonic development in invertebrates
Sea urchin
Drosophila
6 Early embryonic development in vertebrates
Amphibians (Xenopus)
Mammals (Mouse)
Cleavage and formation of the blastula (I)
In animal egg, the first step in embryonic development is the division of the fertilized egg by cleavage into a number of smaller cells (blastomeres), leading in many animals to the formation of a hollow sphere of cells—the blastula (a polarized epithelium surrounding a fluid-filled blastocoel).
Cleavage involves short cell cycles, in which cell division and mitosis eed each other repeatedly without any interventing periods of cell growth (that is, the G1 and G2 phases of the cell cycle). During cleavage therefore, the mass of the zygote does not increase. Thus, the enormous volume of zygote is