The expression profile and promoter analysis of β-N-acetylglucosaminidases in the silkworm Bombyx mori.

β-N-acetylglucosaminidase (GlcNAcase) is a key enzyme in the chitin decomposition process. In this study, we investigated the gene expression profile of GlcNAcases and the regulation mechanism for one of these genes, BmGlcNAcase1, in the silkworm. We performed sequence analysis of GlcNAcase. Using dual-spike-in qPCR method, we examined the expression of Bombyx β-N-acetylglucosaminidases (BmGlcNAcases) in various tissues of silkworm as well as expression changes after stimulation with ecdysone. Using Bac-to-Bac system and luciferase reporter vectors, we further analyzed the promoter sequence of BmGlcNAcase1. The results showed that these proteins have a highly conserved catalytic domain. The expression levels of the BmGlcNAcase genes varied in different tissues, and were increased 48 h after exposure to ecdysone. BmGlcNAcase1 gene promoter with 5'-end serial deletions showed different levels of activity in various tissues, higher in the blood, skin and fat body. Deletion of the region from -347 to -223 upstream of BmGlcNAcase-1 gene abolished its promoter activity. This region contains the binding sites for key transcription factors including Hb, BR-C Z, the HSF and the typical TATA-box element. These results indicate that BmGlcNAcases are expressed at different levels in different tissues of the silkworm, but all are subjected to the regulation by ecdysone. BmGlcNAcase1 promoter analysis has paved a foundation for further study of the gene expression patterns.