Identification of differentially regulated micrornas in cold-hardy insects.

Freeze tolerance in insects is associated with cryoprotectant synthesis and strong metabolic suppression. Freeze avoidance, an alternative strategy in cold-hardy insects, is also characterized by hypometabolism, but possesses significant cellular and physiological differences when compared with freeze tolerance. We hypothesized that microRNAs, non-coding transcripts that bind to mRNA, could play a role in the regulation of energy-expensive mRNA translation in insects exposed to low temperatures. Expression levels of microRNA species were evaluated during cold acclimation of freeze tolerant Eurosta solidaginis and freeze-avoiding Epiblema scudderiana, comparing control (5 degree C) conditions with larvae given sequential exposures to -5 degree C and -15 degree C. MiR-1 levels were significantly elevated in frozen E. solidaginis larvae at -15 degree C, whereas miR-34 levels were unchanged. MiR-1 and miR-34 levels remained stable in E. scudderiana. These data demonstrate differential microRNA expression in frozen versus control insect larvae and highlight contrasting microRNA signatures between freeze tolerant and freeze avoiding species.