Temporal expression patterns of diapause-associated genes in flesh fly pupae from the onset of diapause through post-diapause quiescence

Distinct differences in the temporal expression patterns of genes associated with pupal diapause were noted in the flesh fly, Sarcophaga crassipalpis. The first change observed was a decline in expression of the gene encoding heat shock protein 90 (hsp90) 2 days after pupariation (1 day before the pupa reaches the phanerocephalic stage characteristic of diapause). In contrast, hsp23 and hsp70 transcripts were undetectable in nondiapause samples and d1-d4 diapause-programmed pupae, but were up-regulated just after the start of diapause, 5 days after pupariation. An increase of glycerol content in diapausing pupae was also noted at the start of diapause. The gene encoding proliferating cell nuclear antigen (pcna) was diapause down-regulated, and this occurred in two phases, with the first decline in expression 7 days after pupariation and a second decline in the level of expression on day 14. For pupae held at 20°C for 20 days and transferred to 10°C, diapause ended after 90-100 days at the lower temperature. However, pupae remained in a state of post-diapause quiescence (d100-d150) and sustained diapause-like hsp and pcna expression patterns until adult development was initiated. Glycerol concentrations and survival declined during the post-diapause phase. This study suggests a distinct sequence in the pattern of gene expression at the onset of diapause, but the genes we have monitored do not contribute to the switch to covert developmental potential at the transition from diapause to post-diapause quiescence.