Expression of a sugar clade gustatory receptor, BmGr6, in the oral sensory organs, midgut, and central nervous system of larvae of the silkworm Bombyx mori

Insects taste nonvolatile chemicals through gustatory receptors (Grs) and make choices for feeding, mating, and oviposition. To date, genome projects have identified 69 Gr genes in the silkworm, Bombyx mori; however, the expression sites of these Grs remain to be explored. In this study, we used reverse transcription (RT)-PCR to investigate expression of the B. mori Gr-6 (BmGr6) gene, a member of the putative sugar clade gene family in various tissues. BmGr6 is expressed in the midgut, central nervous system (CNS), and oral sensory organs. Moreover, immunohistochemistry using an anti-BmGr6 antiserum demonstrated that BmGr6 is expressed in cells by oral sensory organs, midgut and nervous system. Furthermore, double-immunohistochemistry indicated that BmGr6 is expressed in midgut enteroendocrine cells, also in CNS neurosecretory cells. In particular, a portion of BmGr6-expressing cells, in both midgut and CNS, secretes FMRFamide-related peptides (FaRPs). These results suggest that BmGr6 functions not only as a taste receptor, but also as a chemical sensor such as for the regulation of gut movement, physiological conditions, and feeding behavior of larvae.