Functional and Evolutionary Relationships Among the RPCH-AKH Family of Peptides

Abstract

SYNOPSIS. The RPCH-AKH peptide family is a group of structurally similar peptides which are apparently widely distributed in arthropods, and which serve a variety of functions in different settings. The first three recognized members of this family were detected and purified based on endocrine activities including color change in crustaceans (RPCH) and effects on energy metabolism in insects (AKH and Compound II). The most recently identified family members, MI and Mil, were found on the basis of neuromuscular activity as well as endocrine effects, and a combination of histological and physiological evidence strongly suggests that at least some of these peptides are localized in neurons including motor neurons which use them as transmitters. Thus this is one of several neuropeptide families with highly conserved structures, but diverse endocrine and neural functions. The significance of structural similarities between family members is unclear. Fortunately the arthropod preparations in which these peptides have been identifiedlend themselves to detailed developmental, anatomical, and physiological analysis, so there is every reason to suppose that molecular biological and physiological investigations currently inprogress will shed significant light on the meaning of the phenomenon of structurally conservative peptide families.