Novel genes differentially expressed between posterior and median silk gland identified by SAGE-aided transcriptome analysis

Serial analysis of gene expression (SAGE) profiles, from posterior and median cells of the silk gland of Bombyx mori, were analyzed and compared, so as to identify their respective distinguishing functions. The annotation of the SAGE libraries was performed with a B. mori reference tag collection, which was extracted from a novel set of Bombyx ESTs, sequenced from the 3′ side. Most of the tags appeared at similar relative concentration within the two libraries, and corresponded with region-specific and highly abundant silk proteins. Strikingly, in addition to tags from silk protein mRNAs, 19 abundant tags were found (≥0.1%), in the median cell library, which were absent in the posterior cell tag collection. With the exception of tags from SP1 mRNA, no PSG specific tags were found in this subset class. The analysis of some of the MSG-specific transcripts, suggested that middle silk gland cells have diversified functions, in addition to their well characterized role in silk sericins synthesis and secretion.

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► In Bombyx mori, majoritary middle silk gland cell mRNA encode proteins of unknown function.
► The presumed secreted proteins may play roles in generating insoluble silk fibroin crystals.
► The majoritary middle silk gland mRNA are absent from the posterior region of the silk gland.
► Key functions are exerted in the middle silk gland, likely related in the spatial organization of the silk proteins.