Transcriptomic analysis of differentially expressed genes in the molting gland (Y-organ) of the blackback land crab, Gecarcinus lateralis, during molt-cycle stage transitions

A transcriptome of the Gecarcinus lateralis molting gland (Y-organ or YO) contained 48,590 contiguous sequences (contigs) from intermolt (IM), early premolt (EP), mid premolt (MP), late premolt (LP), and postmolt (PM) stages. The YO is kept in the basal state in IM by molt-inhibiting hormone (MIH)/cyclic nucleotide-dependent signaling. YO activation in EP requires down-regulation of MIH signaling and activation of mechanistic target of rapamycin (mTOR)-dependent protein synthesis. Transition of the YO to the committed state in MP requires activin/transforming growth factor-beta (TGFP) signaling. YO repression occurs at the end of LP. A total of 28,179 contigs (58%) showed molt stage-specific changes in gene expression. The largest number of differentially-expressed genes (DEGs) were at the IM/EP (16,142 contigs), LP/PM (18,161 contigs), and PM/IM (8290 contigs) transitions. By contrast, the numbers of DEGs were 372 and 1502 contigs for the EP/MP and MP/LP transitions, respectively. DEG analysis of 23 signal transduction pathways showed significant changes in MIH, mTOR, activin/TGF beta, Notch, MAP kinase, and Wnt signaling. Down-regulation of MIH signaling genes in pre-molt is consistent with reduced MIH sensitivity in MP and LP. Up-regulation of mTOR signaling genes in IM and premolt stages is consistent with its role in YO activation and sustained ecdysteroidogenesis. Up-regulation of activin/TGF beta signaling genes in EP and MP is consistent with the role of a myostatin/activin-like factor in YO commitment. Notch, MAP kinase, and Wnt DEG analysis may indicate possible crosstalk with the MIH, mTOR, and activin/TGF beta pathways to integrate other inputs to control YO ecdysteroidogenesis.