Hemolymph Proteins and Molting in Crustaceans and Insects

Abstract

SYNOPSIS. The exoskeleton of crustaceans and insects is formed by cells of the hypodermis, but several hemolymph proteins contribute to the synthesis of the new exoskeleton. These hemolymph proteins share a surprising degree of sequence similarity and are members of the hemocyanin gene family. Copper-containing prophenoloxidases of crustaceans and insects are directly involved in cross-linking and hardening of the exoskeleton during molting and repair. Crustacean cryptocyanin and insect hexamerins lack copper and have probably evolved from a copper-free product of an early hemocyanin gene duplication. These proteins have been implicated in transport of hormones and phenols, and may be used directly as structural components of the new exoskeleton. They are synthesized elsewhere in the body, transported in the hemolymph, and probably taken up by the hypodermis via specific receptors. Hemocyanins have some residual phenoloxidase activity, in addition to their primary role of supplying oxygen to the metabolizing tissues. Thus multiple members of the hemocyanin gene family play vital roles during molting, and a molecular phytogeny of these proteins will contribute to our understanding of the evolution of form and function of these molecules from oxygen transport to molt-related activities. Further studies on the expression of prophenoloxidase, cryptocyanin, hexamerins and hemocyanin, potential marker proteins, may extend our understanding of the relationship between other molting animals in the proposed clade, Ecdysozoa.