Journal of Endocrinology and Reproduction

M. Krishnan ¹, P. Muthumeenakshi ¹, C. Bharathiraja ¹, Sudha Warrier ², T. Subramoniam ²

Affiliations
1 Department of Environmental Biotechnology, Bharathidasan University, Tiruchirappalli-620 024, IN
2 National Institute of Ocean Technology, Pallikaranai, Chennai-600 100, IN

Abstract

Insects and crustaceans offer excellent model systems to study vitellogenesis in invertebrates. This paper gives a comprehensive account of the receptor-mediated yolk protein uptake in a lepidopteran insect Spodoptera litura and a decapod crustacean Scylla serrata. The vitellogenin (Vg) of both these arthropods has been characterized using electrophoretic and immuno-blotting techniques. The Vg's of both the animals are glycolipoproteins and exhibit immunological identity with their respective lipovitellins (Lv's). The physico-chemical characterization of vitellogenin receptors (VgR) of these arthropods revealed several similarities in their molecular weight and binding affinity with vitellins, which was increased considerably by divalent cation calcium. On the other hand, their binding affinity decreased significantly when treated with polyanionic suramin. These properties, along with the strong affinity of crab VgR for mammalian LDL and VLDL, qualify them as members of LDLR superfamily. The receptor-mediated endocytotic entry of Vg into the oocytes has been demonstrated by immunogold electron microscopic technique. The pathway starting from the formation of coated pits to the formation of mature endosomes has been traced using antibodies of Vg and VgR and gold-labeled secondary goat antibody. Use of green immunofluorescence techniques with FITC-tagged Vg antibody of S. litura produced additional evidence for endocytotic yolk protein uptake as well as uneven distribution of yolk within the oocytes.

Keywords

Vitellogenin, Vitellin, Vitellogenin Receptor, Lepidoteran Insect, Decapod Crustacean, Oocyte.

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T. Subramoniam ¹

Affiliations
1 National Institute of Ocean Technology, (Ministry of Earth Sciences, Govt. of India) Velachery-Tambaram Road, Pallikaranai, Chennai -601 302, IN

Abstract

This paper reviews information available on the composition of yolk and the pattern of yolk utilization during embryogenesis in an intertidal crab, Emerita asiatica, from the east coast of India. Emerita yolk primarily exists as a glycolipoprotein complex, conjugated with carotenoid pigment. In addition, free lipid globules and glycogen droplets are also stored in the ooplasm. Another feature of interest is the conjugation of several steroidal hormones such as ecdysteroids, estrogen and progesterone with the yolk molecules. The stage-specific release of a host of hydrolytic enzymes splits up the complex yolk molecules which not only serve as raw organic substrates for tissue build up, but also function as regulatory factors during embryogenesis. For example, the regulated release of active ecdysteroids from the conjugates at specific time during embryogenesis not only triggers embryonic cuticle formation but also accomplishes larval molting and egg hatching. In conclusion, the study on the Emerita yolk utilization provides information on energy release for embryogenesis as well as abbreviated larval development that occurs within the brooding egg in Crustacea.

Keywords

Crustacea, Emerita, Embryonic Ecdysteroids, Larval Storage Proteins, Yolk Utilization.

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T. Subramoniam ¹

Affiliations
1 CSIR-Emeritus Scientist, Department of Zoology, University of Madras, Chennai 600 025, IN

Abstract

Crustacean yolk proteins are complex molecules comprised of a high-density lipoprotein conjugated to carbohydrates and carotenoid pigments. They are invariably derived from their precursor protein, vitellogenin, synthesized extra ovarially in sites such as hepatopancreas and fat body. The specific uptake of this precursor protein into the oocytes is aided by a vitellogenin receptor present on the oocyte membrane. The present paper deals with the molecular characterization of vitellogenin receptor in an edible crab, Scylla serrata.

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T. Subramoniam ¹

Affiliations
1 Department of Zoology, University of Madras, Guindy Campus, Chennai-600025, IN

Abstract

Endocrine regulation of reproduction and molting in Crustacea was first demonstrated by the experimental evidence that eyestalk removal led to accelerated ovarian maturation and the onset of precocious molting. Subsequent immunocyto chemical studies as well as HPLC separation of neuropeptides followed by suitable bioassay established the occurrence of two neuropeptides namely gonad inhibiting (GIH) and molt-inhibiting (MIH) neurohormones in the X-organ/sinus gland complex of stalk-eyed malacostracan crustaceans. While the molt promoting hormones have been decidedly shown to be the ecdysteroids, as in other arthropods, many hormonal factors of diverse chemical nature have been proposed for controlling female reproduction. Neurosecretory hormones from brain/thoracic ganglia, methyl farnesoate, a structural homologue to insect Juvenile hormone III (JH III) and a variety of steroidal hormones are the principal candidates for control of female reproduction, especially viteilogenesis. As molting continue to occur in the adult crustaceans, hormonal coordination of both molting and reproduction becomes vital to accomplish fast body growth and increased fecundity in these aquaculture-targeted arthropods. Steroidal control of such a coordination is stressed in this review.

Keywords

Crustaceans, Molting, Neuropeptides.

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