Long SAGE analysis of genes differentially expressed in the midgut and silk gland between the sexes of the silkworm<i>Bombyx mori</i>

Abstract

There are great differences in silk production efficiency and quality between the male and female domestic silkworm (Bombyx mori). Many genes act together but are differentially expressed between the sexes during silk biosynthesis. Two long serial analyses of gene expression (SAGE) libraries were constructed from the midguts and silk glands of both males and females of a sex-limited strain using 5^th instar larvae, yielding in total 96,713 and 98,126 SAGE tags, respectively. Among these tags, 202 were analyzed (p < 0.05 and at least a 2.0-fold change between sexes). Overall, 69 genes were then annotated in detail and 15 tags were annotated with expressed sequence tags (ESTs) based only on the NCBI, SilkDB and long-SAGE libraries. Of these genes, only three could be ascribed to sexual disparity as described by microarray-based expression resources of day three of 5th instar in Dazao B. mori microarray database (BmMDB). The other 66 genes were considered the SAGE-extracted genes that are differentially expressed between the sexes of the whole 5th instar larvae. Among the 66 genes and 15 tags, genes (and gene families) sex-specific storage-protein 1 gene (Sp1), low molecular mass 30 kDa lipoprotein 19G1 gene (Lp-c19), serine proteinase family [serine protease precursor gene (Spp) and chymotrypsin-like serine protease gene (Ctlp)], Serpins (Spi1 and Spi2) and Ser1, and the tag 1161 (annotated EST No. BY926524), which are involved in protein digestion in the midgut, synthesis of silk and inhibition of protein disintegration in silk gland, were verified by the remarkable disparities in gene expression between the sexes. The established SAGE library would contribute to the further identification of genes related to sexual disparity in silk protein production efficiency.

Key words: Bombyx mori, sexes, silk protein production efficiency, long-SAGE, differentially expressed genes.