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

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.