Changes in gene expression linked with adult reproductive diapause in a northern malt fly species: a candidate gene microarray study

Abstract

Background: Insect diapause is an important biological process which involves many life-history parameters important for survival and reproductive fitness at both individual and population level. Drosophila montana, a species of D. virilis group, has a profound photoperiodic reproductive diapause that enables the adult flies to survive through the harsh winter conditions of high latitudes and altitudes. We created a custom-made microarray for D. montana with 101 genes known to affect traits important in diapause, photoperiodism, reproductive behaviour, circadian clock and stress tolerance in model Drosophila species. This array gave us a chance to filter out genes showing expression changes during photoperiodic reproductive diapause in a species adapted to live in northern latitudes with high seasonal changes in environmental conditions.

Results: Comparisons among diapausing, reproducing and young D. montana females revealed expression changes in 24 genes on microarray; for example in comparison between diapausing and reproducing females one gene (Drosophila cold acclimation gene, Dca) showed up-regulation and 15 genes showed down-regulation in diapausing females. Down-regulation of seven of these genes was specific to diapause state while in five genes the expression changes were linked with the age of the females rather than with their reproductive status. Also, qRT-PCR experiments confirmed couch potato (cpo) gene to be involved in diapause of D. montana.

Conclusions: A candidate gene microarray proved to offer a practical and cost-effective way to trace genes that are likely to play an important role in photoperiodic reproductive diapause and further in adaptation to seasonally varying environmental conditions. The present study revealed two genes, Dca and cpo, whose role in photoperiodic diapause in D. montana is worth of studying in more details. Also, further studies using the candidate gene microarray with more specific experimental designs and target tissues may reveal additional genes with more restricted expression patterns.

Figure 1

Normalized fold expression of the candidate genes in microarray analysis. Normalized fold expression of the candidate genes in diapausing females compared to reproducing females, in diapausing females compared to young females and in reproducing females compared to young females in microarray analysis. Up-regulation is shown with the positive values and down-regulation with the negative values on y-axis. Significance levels: *0.05 > P > 0.01, **0.01 > P > 0.001, ***P < 0.001. In cpo gene down-regulation and in tilB and Hsp26 genes up-regulation was more than 6-fold and is indicated with numbers in the boxes.

Figure 2

Normalized fold expressions of candidate genes in qRT-PCR analysis. Normalized fold expressions and standard deviations of cpo, CG7650, tilB, Fmr1 and Dca genes in diapausing and reproducing females in qRT-PCR analysis.