Vitellogenesis with special emphasis on Indian fishes |
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| Authors: | P Nath R Sahu Sk Kabita D Bhattacharya |
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| Institution: | (1) Department of Zoology, Visva Bharati University, Santiniketan, West Bengal, 731 235, India |
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| Abstract: | Oocyte growth in most oviparous vertebrates including fish is due to the formation of yolk, and eggshell proteins (zona radiata
proteins). Zonagenesis leads to the formation of zona radiata proteins in oocytes, which play an important role during oogenesis,
whereas vitellogenesis leads to the formation of yolk in oocytes through a series of events during which the yolk precursor
protein vitellogenin (Vg) is synthesized and secreted from liver into blood from where it is sequestered into the developing
oocytes and thereafter proteolytically cleaved to form yolk proteins (YPs) and finally deposited in the ooplasm. Much research
has been done in many fish species with respect to the number and nature of Vg and YPs and their probable functions during
fish reproduction. Recent findings of multiplicity of Vg molecules in fishes reject the earlier view of a single-Vg model
and have led scientists to explore the functions of individual Vg and their YP derivatives, lipovitellin, phosvitin, and β′-component.
Two distinct types of Vg or Vg genes, containing or encoding the three YPs, have been detected in many teleosts. A third unusual,
incomplete, phosvitin-poor Vg has been described recently in many fishes. In comparison to much of the information on vitellogenesis
in many fishes very little is known for Indian fishes. In India research has been done in a few species such as the catfish,
Heteropneustes fossilis and Clarias batrachus, the murrel, Channa punctatus and the Indian major carps, Labeo rohita and Cirrhinus mrigala. Immunological and biochemical analyses suggest the occurrence of multiple forms of Vg and their YP derivatives. The synthesis
and incorporation of Vg are regulated by gonadotropin (GTH) and estradiol-17β (E2). A differential role between estrone (E1) and estriol (E3) has been demonstrated for Vg synthesis. Enzyme-linked immunosorbent assays (ELISAs) for Vg have been developed to measure
plasma Vg. Finally the different roles of Vg1 (HAI) and Vg2 (HAII) on vitellogenesis have been demonstrated. However, more
research remains to be carried out in other fish species with respect to the number and nature of Vg and YPs and their genes
in order to describe their reproductive functions. |
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| Keywords: | Fish Estradiol-17β Gonadotropin Vitellogenin Vitellogenesis Zonagenesis Yolk proteins |
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