Tissue-specific variation of heat shock protein gene expression in relation to diapause in the bumblebee Bombus terrestris

Diapause-associated expression patterns of heat shock protein genes (hsp) were determined in the queen of the bumblebee Bombus terrestris, a pollination insect. Partial cDNA sequences of three hsp genes - shsp, hsc70 and hsp90 - were obtained, and the deduced amino acid sequences were found to be highly homologous with corresponding hsp of hymenopteran insects. Using northern hybridization, the transcript level of each gene was compared in six stages relating to diapause: pre-mating, post-mating, chilling for 1, 2 and 3 months, and post-chilling. The transcript level was also compared in four tissues of adult queens: brain, thoracic muscle, gut and ovary. The transcript levels of the three hsp genes changed at various rates in relation to diapause, and each pattern was highly tissue-specific. Overall patterns of hsc70 and hsp90 expression were similar in each tissue. The shsp level in the brain was downregulated after 1 month chilling, but its level in the ovary was upregulated during a long chilling period; levels in muscle and gut did not change in relation to diapause. The levels of both hsc70 and hsp90 in muscle were gradually upregulated in late diapause and postdiapause stages, but levels in the ovary were downregulated during the chilling period, while levels in the brain and gut did not change in relation to diapause. Our results show that the three hsp genes were differentially regulated in stage- and tissue-specific manners throughout diapause, and suggest unique physiological roles for these genes in relation to diapause in each tissue of queen bumblebees.