Light-dependent transcriptional events during resting egg

26 27 Rotifer resting eggs often have to endure harsh environmental conditions during the diapause phase. 28 They are stimulated by light to hatch. In order to study the hatching mechanism, we observed 29 resting eggs and measured their transcriptional expression under different light exposure periods 30 (total darkness, and after 30 min, and 4h light). By using differential-display reverse transcription 31 PCR (DDRT-PCR), we isolated 80 genes that displayed different expression patterns in response to 32 the three light treatments: 20 genes were expressed in total darkness, 40 different genes were 33 differentially expressed under 30 min light, and 20 further genes were expressed after 4h of light. 34 The resting eggs showed no phenotypic differences in embryonic development during the 4h 35 illumination period. In general, the expression patterns of the analyzed genes in resting eggs were 36 differentially modulated by light exposure time. In total darkness, resting eggs mainly express genes 37 encoding cell defense and homeostasis functions. In the 30 min illumination group, we found 38 enriched expression of genes encoding fatty acid metabolism-related components, including Acyl39 CoA dehydrogenase (ACAD). Genes encoding cellular and embryonic developmental functions 40 were highly observed in the 30 min-illuminated group but were not observed in the 4h-illuminated 41 group. Real-time RT-PCR revealed that several transcripts such as encoding V-type H(+)42 translocating pyrophosphatase (V-PPase) and Meckelin had prolonged expression levels when 43 exposed to light for 4 hours. In the 4h illuminated group, the RecQ protein-like 5 (RECQL5) gene 44 was enriched. This RECQL5 gene may be expressed to protect the developing embryo from 45 continuous light exposure. The data presented in this study indicate that DDRT-PCR-aided gene 46 screening can be helpful to isolate candidate genes involved in the hatching process. Therefore, this 47 paper provides new insights regarding the light-mediated molecular response of rotifer resting egg 48 hatching. 49 50