Putative Pacemakers in Crayfish Procambarus clarkii Show Circadian Oscillations in Levels of mRNA for Clock Genes under Different Light Rhythm

Abstract

In the circadian rhythm mechanism, cycle (Cyc), clock (Clk), cryptochrome (Cry) are three core clock genes that constitute complex mechanism controlling organisms to follow a 24-hour oscillation cycle. In the present study, the major clock genes, i.e. PcCyc, PcClk, PcCry1 were cloned from crayfish Procambarus clarkii. The putative functions as well as physical and chemical properties of the resolved proteins were analyzed by various bioinformatic methods. Real-time quantitative PCR technique was used to explore the mRNA expression of the PcCyc, PcClk, PcCry1 in brain, eyestalk, and hepatopancreas tissues of P. clarkii. In order to examine circadian rhythm of selected clock genes in the species, the experiment was carried out under three different light conditions, namely: (a) 12 h of light and dark periods per day (12LD), (b) 24 h of constant darkness (24DD) and (c) 72 h of constant darkness (72DD). The obtained results showed essential correlation in the mRNA expression levels of PcCyc and PcClk genes under similar light conditions. It indirectly suggests that the PcCYC and PcCLK proteins might be involved in the transcriptomic regulatory mechanism of all other genes within the core-clock network. The mRNA expression levels of the PcCry1 gene were highly variable, differing significantly in relation to the various illumination conditions and sampled tissues. The obtained results seem to follow the pattern evidencing the sensitivity of PcCry1 gene to the light signals. It firmly supports the gene’s role in the conversion mechanism of light signals into optical signals, which is engaged in the generation and control of circadian rhythmicity.