The molecular evolution of the allatostatin precursor in cockroaches

Allatostatins (ASTs) of the Tyr/Phe-Xaa-Phe-Gly Leu/Ile-NH2 family are a gr oup of insect neuropeptides that inhibit juvenile hormone biosynthesis by t he corpora allata. We have obtained genomic DNA sequences that specify the preproallatostatin precursor for the cockroaches, Blatta orientalis, Blatte lla germanica, Blaberus craniifer and Supella longipalpa. The sequences obt ained are similar to those of Diploptera punctata and Periplaneta americana reported previously. The precursors of all these cockroach species are sim ilar in size, and the organization of the ASTs that they contain (there are 13 or 14, depending on the species) have been conserved. With the sequence s of these precursors, and using the homologous sequence in the orthopteran Schistocerca gregaria as an outgroup, a phylogenetic analysis using parsim ony was carried out. The dendrograms obtained from these analyses, using th e amino acid as well as the nucleotide sequences, are comparable with curre nt models for cockroach phylogeny. Parsimony analysis was also used to stud y the genealogy of the different ASTs within the same precursor. Results su ggest that the AST sequences were generated through a process of internal g ene duplication which occurred before these species diverged from each othe r in evolutionary time. (C) 1999 by Elsevier Science Inc.