Genes encoding two cystatins in the flesh fly Sarcophaga crassipalpis and their distinct expression patterns in relation to pupal diapause.

Two genes encoding cystatins, cysteine proteinase inhibitors, were cloned from the flesh fly Sarcophaga crassipalpis. One, sarcocystatin A (abbreviated Scys-A and SCYS-A for the gene and protein, respectively) was previously cloned from Sarcophaga peregrina, but the other is novel. Here the novel gene is named sarcocystatin B (abbreviated Scys-B and SCYS-B for the gene and protein, respectively). Tissue distribution of the two sarcocystatins differs: the fat body is the major site of Scys-A expression, while Scys-B is present in both the fat body and gut. Both Scys-A and -B are developmentally regulated, but their expression patterns also differ. Scys-A transcripts are present in both diapause- and non-diapause-destined third instar wandering larvae, and are then downregulated throughout pupal diapause. By contrast, Scys-B transcripts are only weakly expressed during the third larval instar but are highly upregulated in early diapause. The upregulation of Scys-B in early diapause suggests a possible role for this proteinase inhibitor in halting development.