Differential regulation of heat shock protein genes by temperature in relation to initial diapause in the egg of the katydid Paratlanticus ussuriensis

Abstract

AbstractThe lifecycle of Paratlanticus ussuriensis Uvarov can extend for longer than 1 year (plurennial) as a result of prolonged diapause. Eggs can overwinter by entering a facultative initial diapause in the early embryonic stage within the egg, followed by further overwintering by entering an obligatory final diapause at the fully developed embryonic stage. The initial diapause is temperature‐dependent and initiated by continuous incubation at 20 °C but not at 30 °C. To understand the mechanism of initial diapause at the molecular level, cDNAs of small heat shock protein genes (shsp), hsp90, as well as three hsp70 genes (hsp70a, hsp70b and hsp70c), are determined and the transcript levels of the five hsp genes are compared in eggs incubated at 20 or 30 °C for 60 days after oviposition using real‐time reverse transcriptase‐polymerase chain reaction analysis. At 30 °C, transcript levels of shsp, hsp70a, hsp70b and hsp90 increase in eggs with age. However, hsp70c levels uniquely peak only in 25‐day‐old eggs, corresponding to the time of initial diapause. At 20 °C, distinct levels of shsp, hsp70a and hsp90 appear in some stages and fluctuate throughout the 60‐day observation period, although both hsp70b and hsp70c are undetectable. These results suggest that each hsp may play a specific role in relation to initial diapause. In addition, up‐regulation of hsp70c may be associated with the mechanism of embryonic activation for averting initial diapause in warmer conditions.