High temperature interrupts initial egg diapause in Paratlanticus ussuriensis and induces expression of a heat shock protein 70 gene

Diapause of Paratlanticus ussuriensis eggs can be prolonged to more than 1 year depending on environmental conditions. Eggs can enter an initial facultative diapause in the early embryonic stage and then enter a final obligatory diapause in the fully developed embryo stage. Initial diapause is temperature-dependent; it is initiated at 20 °C and inhibited at 30 °C. To determine the effects of temperature on the mechanism of initial diapause of P. ussuriensis eggs, we compared weight and DNA and RNA contents of eggs that were incubated at either 20 °C or 30 °C for 60 days after oviposition. Weight and total DNA of eggs were constant when incubated at 20 °C but gradually increased when incubated at 30 °C. Total RNA content increased over 15 days then remained at a high level when eggs were incubated at 30 °C whereas RNA content was at a constant low level when eggs were incubated at 20 °C. In addition, we cloned the heat shock protein 70 (hsp70) gene from P. ussuriensis and determined its expression levels at different temperatures. Hsp70 was not detectable until 20 days after oviposition. Its level increased at 50 and 60 days when incubated at 30 °C, but increased only slightly when incubated at 20 °C. Our results suggest that high temperature inhibits the initial diapause and induces overall transcription activity in the eggs. Upregulation of hsp70 expression at high temperatures may be associated with further embryonic development of the eggs.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Paratlanticus ussuriensis eggs entered a facultative initial diapause. ► Initial diapause was temperature-dependent. ► Egg weight, DNA and RNA contents were increased at 30 °C. ► The full cDNA of hsp70 gene was cloned from P. ussuriensis. ► Hsp70 level increased after 50 days post-oviposition at 30 °C.