The angiotensin-converting enzyme (ACE) gene family of Bombyx mori

We previously reported regarding an ecdysone-inducible angiotensin-converting enzyme (ACE) gene. We found another four ACE genes in the Bombyx genome. The present study was undertaken to clarify the evolutionally changed function of the ACE of Bombyx mori. Core regions of deduced amino acid sequences of ACE genes were compared with those of other insect ACE genes. Five Bombyx genes have the conserved Zn²⁺-binding-site motif (HEXXH); however, BmAcer4 has only one and BmAcer3 has no catalytic ligand. BmAcer1 and BmAcer2 were expressed in several organs. BmAcer3 was expressed in testes, and BmAcer4 and BmAcer5 were expressed in compound eyes; however, the transcription levels of these three genes were very low. Quantitative RT-PCR and Western analysis were conducted to determine the tissue distribution and developmental expression of BmAcer1and BmAcer2. Transcripts of BmAcer1 and BmAcer2 were found in the reproductive organs during the larval and pupal stages. BmAcer1 was dominant in fat bodies during the feeding stage and showed high expression in the epidermis, wing discs, and pupal wing tissues after the wandering stage. Its expression patterns in epidermis, wing discs, and wing tissues resembled the hemolymph ecdysteroid titer in the larval and pupal stages. Acer1 was observed in the hemolymph at all stages, appearing to be the source of it are fat bodies, wings, and epidermis, and functioning after being secreted into the hemolymph. BmAcer2 was abundant in the midgut during the feeding stage and after the wandering stage and in silk glands after the pupal stage. We conclude that the evolution of BmAcer occurred through duplication, and, thereafter, functional diversification developed.