Download CSIR NET UNIT 5B : Developmental Biology Notes – Gastrulation, Early Development In Amphibians

CSIR NET Developmental Biology Notes

CSIR NET UNIT 5 Developmental Biology – a very important unit as per the CSIR NET exam with a good weightage. Nearly 30+ marks of questions are asked from this UNIT every year. So one must not skip studying this unit at all. Some students find it a little difficult to understand the concepts. Thus it is suggested to prepare this unit beforehand and avoid last-minute study. Atleast the important topics from this unit must not be skipped.

Check the Important Topics List from CSIR NET Unit 5 here

Important REFERENCE BOOKS For CSIR NET Life Science UNIT 5

• Developmental Biology by Scott F. Gilbert
• Principles of Development by Lewis Wolpert, Cheryll Tickle

In this notes Topics related to Gastrulation / Early Development In Amphibians have been covered. CSIR NET Developmental Biology Notes

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FATE MAP

• The surface of the animal hemisphere will become the cells of the ectoderm (skin and nerves),
• the vegetal hemisphere surface will form the cells of the gut and associated organs (endoderm), and the mesodermal cells will form from the internal cytoplasm around the equator.
• This general fate map is thought to be imposed upon the egg by the transcription factor VegT and the paracrine factor Vg1.
• The animal third of the embryo produced only ventral epidermis, while the marginal cells (which normally produced mesoderm) generated epidermal and neural tissue.
• The vegetal third (which usually produces endoderm) produced a mixture of ectoderm and mesoderm.
• Joseph and Melton (1998) demonstrated that embryos that lacked functional Vg1 lacked endoderm and dorsal mesoderm.

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Cortical Rotation

• During cortical rotation, the plasma membrane and cortex (the cytoplasmic region just below the plasma membrane) rotate relative to the inner cytoplasm.
• The pigmentation of frog eggs makes it possible to observe this process visually and results in a gray area, called the gray crescent
• Rearrangement is mediated by the ATPase Kinesin
• Rearrangement of cytoplasm helps in the determination of dorsal & ventral axis

Certain Experiments Related to Cortical Rotation

1. If cortical rotation occurred at about 90° of the sperm entry instead of 30°, then the dorsal lip of the blastopore will be formed as the same region where sperm entered
2. If the egg is activated without sperm, then cortical rotation occurs but the direction cannot be predicted
3. If sperm entry does not induce cortical rotation then a Grey crescent will not form and embryonic development will not take place.

EARLY-GASTRULATION

Blastopore Formation

• The bottle cells of the margin move inward to form the dorsal lip of the blastopore.
• The mesodermal precursors involute under the roof of the blastocoel
• Animal pole will change as gastrulation continues.

Involution of Marginal zone cells

CSIR NET Developmental Biology Notes by Biotecnika

• movement of inside MZ cells dependent on ectoderm cells of blastocoel roof secreting fibronectin
• Fibronectin is essential for mesodermal cell involution during gastrulation

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MID-GASTRULATION

Formation of the Archenteron = Convergent Extension of the Dorsal Mesoderm

• The archenteron forms and displaces the blastocoel Cells to migrate from the lateral and ventral lips of the blastopore into the embryo.
• The cells of the animal hemisphere migrate down toward the vegetal region, moving the blastopore to the region near the vegetal pole.

Toward the end of gastrulation

• The blastocoel is obliterated
• The embryo becomes surrounded by ectoderm.
• The endoderm has been internalized
• The mesodermal cells have been positioned between the ectoderm and endoderm.

Epiboly of the Ectoderm – Contd…

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