Does epigenetic gene silencing regulate diapause in Sarcophaga crassipalpis?

Insect diapause is typically characterized by developmental arrest and species specific physiological changes. Although physiological changes associated with diapause have been characterized for a number of species, the molecular mechanisms that regulate developmental arrest are not well understood even though many genes have been shown to be differentially expressed during diapause. In addition, many studies on the regulation of diapause have looked at changes in gene expression in insects that are already in diapause while less focus has been placed on changes that occur during diapause initiation. This study measured the transcript abundance of eight genes known to silence gene expression via either chromatin remodeling (HP1 and Su(var)3-9,and dnmt) and/or RNA interference (piwi, homeless, aubergine, Argonaute, and sticky). The mRNA abundance of most of the genes measured was either downregulated (Argonaute and homeless) or unchanged (piwi, aubergine, sticky, and dnmt) in photosensitive first instar Sarcophaga crassipalpis larvae exposed to short day (SD), diapause inducing conditions compared to larvae reared under long day (LD), diapause averting conditions. However, transcript abundance of HP1 and Su(var)3-9 was significantly higher in SD larvae compared to LD larvae. Given these data, we propose that diapause initiation may be regulated, in part, by changes in the chromatin structure of larvae exposed to SD conditions.