Molecular cloning, characterization and expression analysis of a doublesex gene from daphnia carinata (Crustacea: Cladocera) during different reproductive stages

To better understand the reproductive transformation mechanism of Daphnia carinata, a Doublesex (Dsx) gene was cloned based on rapid amplification of cDNA ends (RACE), and was designated DapcaDsx2. Next, we compared similarities and assumed homology based on deduced amino acid sequences. It showed 97.52, 87.94, and 85.11% identity to orthologous genes in D. magna, D. pulex, and D. galeata respectively. Phylogenetic analysis revealed that DapcaDsx2 clustered in the same class, and was evolutionarily more distant to sequences from other species. qRT-PCR showed that DapcaDsx2 was most abundantly expressed during sexual reproduction (P < 0.05). Using digoxigenin-labeled RNA probes, we studied DapcaDsx2 expression in parthenogenetic and sexual females by whole-mount in situ hybridization. The results revealed that DapcaDsx2 was mainly expressed in the second antennae and several sites of the ventral carapace, whereas higher expression levels were found in sexual than in parthenogenetic females. This suggests that the DapcaDsx2 gene is involved in switching modes of reproduction and in sexual differentiation.