Molecular characterization of the gene checkpoint homolog 1 in Daphnia carinata during different reproductive phases.

Full-length cDNA of the gene checkpoint homolog 1 (Chk1) was cloned from Daphnia carinata and designated DcarChk1. DcarChk1 cDNA was 1817 bp in length and encoded a 497-amino acid polypeptide. Phylogenetic analyses revealed that DcarChk1 was most closely related to Chk1 of Daphnia pulex, followed by homologous genes of insects. Expression of DcarChk1 was higher in adult Daphnia than in larvae, and significantly higher in males than females, as determined by real-time polymerase chain reaction analysis. Using whole-mount in situ hybridization techniques, DcarChk1 in parthenogenetic females was found to be expressed mainly on the head surface, capillus, and carapace valve edge. In contrast, in sexual females, DcarChk1 was expressed mainly in the joint of the second antenna, and in the thoracic limbs and capillus. These results suggest that DcarChk1 plays a significant role in both the growth and development, as well as in regulating reproductive plasticity, in D. carinata.