Novel gene encoding precursor protein consisting of possible several neuropeptides expressed in brain and frontal ganglion of the silkworm, Bombyx mori

A novel gene (BmK5) expressed in the central nervous system of the silkworm, Bombyx mori, was isolated using a cDNA subtraction method. BmK5 was first cloned as a candidate regulator of diapause hormone release from subesophageal ganglion via corpus cardiacum–corpus allatum into the hemolymph; however, subsequent analyses revealed that the gene expression patterns in brain–subesophageal ganglion complexes did not differ between diapause and nondiapause egg producers. The deduced amino acid sequence showed the characteristics of secretory protein precursor or nuclear localization protein. Immunohistochemical experiments with an anti-BmK5 antibody revealed that BmK5 precursor protein exists in the cytoplasm of specific cells of brain and frontal ganglion, but not in the nuclei. In addition, a peptide (GSGTKVGGAGAATKVVTKSGS-NH2) possibly processed from the BmK5 precursor protein was immunohistochemically detected in the axons connecting the anti-BmK5 antibody-positive cells to the neurohemal organ, corpus cardiacum–corpus allatum. These results suggest that BmK5 encodes a precursor of the novel neurosecretory protein and that several mature peptides are released into the hemolymph via the corpus cardiacum–corpus allatum, although the functions of these peptides are yet unclear.