Mechanisms and control of vitellogenesis in crustaceans

Abstract

Crustaceans produce complex yolk proteins to meet the substrate and energy requirements of embryonic development. Early electron microscopic investigations point to a biphasic yolk synthesis, first within the ovary, followed by heterosynthesis at extra-ovarian sites. Recent advances in molecular techniques have enhanced our understanding of the genetic control of yolk synthesis in crustaceans. Amino acid sequencing of crustacean vitellogenin (Vg) has enabled the elucidation of the cDNA sequence associated with it, the identification of genes, and the examination of their expression patterns in different tissues. Yolk processing in crustaeans involves cleavage of the pro-Vg at consensus sites by subtilisin-like endoproteases within the hepatopancreas, hemolymph and oocytes. The structural elucidation of crustacean yolk proteins, as well as the comparison of amino acid sequences of vitellogenins from various crustacean species, has revealed molecular phylogenetic relationships not only among them but also with other large lipid transfer lipoproteins of disparate function. The combinatorial effects of eyestalk neuropeptides and a variety of trophic hormones achieve the hormonal coordination of molting and reproduction. Biogenic amines secreted by the central nervous system may also play an integrative role by stimulating neuropeptide secretion.