A comparative study on vitellogenin receptor of a lepidopteran insect (Spodoptera litura) and a decapod crustacean (Scylla serrata): Phylogenetic implication and co-evolution with vitellogenins M. Krishnan 1 , P. Muthumeenakshi 1 , C. Bharathiraja 1 , Sudha Warrier 2 and T. Subramoniam 2 1.Department of Environmental Biotechnology, Bharathidasan University, Tiruchirappalli-620 024, India. 2. National Institute of Ocean Technology, Pallikaranai, Chennai-600 100, India Summary 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. Key words: Vitellogenin, vitellin, vitellogenin receptor, lepidoteran insect, decapod crustacean, oocyte J Endocrinol Reprod 12 (2008) 1: Original Article Correspondence to be addressed to: Dr. M. Krishnan, Ph.D., Email: profmkrish@yahoo.com Introduction There is considerable commonality between insects and crustaceans in respect of vitellogenin (Vg) synthesis and uptake into the oocyte during ovarian maturation. In both the cases Vg precursor molecule of the major egg yolk protein is synthesized outside the ovary and transported in the hemolymph to the oocytes. The higher dipteran flies, such as Drosophila melanogaster, are an exception to this rule in that synthesis of yolk peptides occurs in the ovary and the externally derived Vg is synthesized in the fat body (Bowens and Pathirana, 2002). Similarly, in the penaeid shrimps yolk proteins are synthesized both in the hepatopancreas and the ovary (Wilder et al., 2002). However, in the other large-bodied decapods such as crabs, lobsters, crayfish and freshwater prawns, almost all yolk precursor proteins are synthesized in the hepatopancreas, with only a limited synthesis within the ovary (Rani and Subramoniam, 1997; Yang et al., 2000; Chan et al., 2005). In addition to Vg, other major hemolymph proteins, such as the lipid transport lipoprotein lipophorin, are also deposited in significant quantities in the eggs of lepidopteran insects (Telfer, 2002). In the crustaceans too, hemolymph lipoproteins other than Vg are known to be sequestered into the oocytes during vitellogenesis (Subramoniam and Gunamalai, 2004). However, the sequestration of hemolymph Vg is invariably mediated by specific membrane receptors present on the oocytes. The Vg receptors (VgR) are also thought to mediate uptake of other lipid transport lipoproteins such as lipophorin in insects and low-density lipoproteins in birds into the eggs (Byrne et al., 1989). VgR has been characterized from molecular perspectives mainly in birds, although insects and crustaceans have received some attention. Further, VgR of birds and other oviparous vertebrates are different from that of invertebrates in terms of molecular size and, probably, mode of ligand binding during yolk protein internalization (Li et al., 1988). In the present study an attempt has been made to compare VgR of a lepidopteran insect, Spodoptera litura, and a decapod crustacean, Scylla