Cloning and expression of a Chk1 gene in Daphnia pulex during different modes of reproduction

The full-length cDNA of a Chk1 gene (DpChk1) was cloned from Daphnia pulex using RACE method. This cDNA is 1767 bp in length, consisting of a 1497 bp open reading frame encoding 498 amino acid protein. The deduced DpChk1 protein sequence contains phosphorylation sites, three conserved Ser-Gln and Thr-Gln motifs and shares 51–55 % similarity with A.pisum, M. rotundata,D. melanogaster, A. echinatior, B. terrestris, R. pulchellus and M. occidentalis, respectively. Gene expression analysis showed that Chk1 is differentially expressed in D. pulex during different reproductive modes. DpChk1 expression in sexually-reproducing females and males is significantly higher than in parthenogenetic Daphnia. Whole-mount in situ hybridization revealed that DpChk1 was expressed during two kinds of reproductive modes. In parthenogenetic females, hybridization signals were found in the antennae and thoracic limb, whereas expression levels in the corresponding sites of sexually-reproducing females were relatively strong, DpChk1 could not be detected in the gonads of ephippial and parthenogenetic females. Taken together, these different reproductive stages and sex specific expression patterns are regulated temporally and spatially. We speculate that DpChk1 may be involved in conversion between different stages of reproduction and in sexual differentiation in D. pulex.