Light-dependent transcriptional events during resting egg hatching of the rotifer Brachionus manjavacas

Rotifer resting eggs often have to endure harsh environmental conditions during the diapause phase. They are stimulated by light to hatch. In order to study the hatching mechanism, we observed resting eggs and measured their transcriptional expression under different light exposure periods (total darkness, and after 30 min, and 4 h light). By using differential-display reverse transcription PCR (DDRT-PCR), we isolated 80 genes that displayed different expression patterns in response to the three light treatments: 20 genes were expressed in total darkness, 40 different genes were differentially expressed under 30 min light, and 20 further genes were expressed after 4 h of light. The resting eggs showed no phenotypic differences in embryonic development during the 4 h illumination period. In general, the expression patterns of the analyzed genes in resting eggs were differentially modulated by light exposure time. In total darkness, resting eggs mainly expressed genes encoding cell defense and homeostasis functions. In the 30 min illumination group, we found enriched expression of genes encoding fatty acid metabolism-related components, including Acyl-CoA dehydrogenase (ACAD). Genes encoding cellular and embryonic developmental functions were highly observed in the 30 min-illuminated group but were not observed in the 4 h-illuminated group. Real-time RT-PCR revealed that several transcripts such as encoding V-type H(+)-translocating pyrophosphatase (V-PPase) and Meckelin had prolonged expression levels when exposed to light for 4 h. In the 4 h illuminated group, the RecQ protein-like 5 (RECQL5) gene was enriched. This RECQL5 gene may be expressed to protect the developing embryo from continuous light exposure. The data presented in this study indicate that DDRT-PCR-aided gene screening can be helpful to isolate candidate genes involved in the hatching process.