RNAi analysis of Doublesex1 expression in Daphnia pulex Leydig, 1860 (Cladocera)

To explore the role of the Doublesex gene (Dsx1) in the switching between reproductive modes in Daphnia pulex Leydig, 1860, we performed gene silencing using RNA interference (RNAi). We also investigated the expression of gfp (Green Fluorescent Protein) by quantitative-PCR, and the expression of Dsx1 mRNA after RNAi by real-time PCR. Dsx1 expression was significantly greater in males than in females, and was down-regulated in experimental groups compared with the control group. The decrease was more significant in females (35% of controls) than males (47% of controls). The gene fragment of Dsx1 amplified by PCR was ligated to the pEASY-Blunt vector to obtain the recombinant plasmid expressed recombinant protein induced by isopropyl-β-D-thiogalactoside (IPTG). After having been purified by Ni-column affinity chromatography, the recombinant protein as antigen was used to immune rabbits. The antiserum was successfully purified by the protein A method to obtain the Dsx1 polyclonal antibody, an IgG concentration of 2.65 mg/ml, titer 240 000. Western blotting showed that RNAi treatment significantly reduced DSX1 protein levels. Wholemount immunofluorescence analysis revealed that the fluorescence intensity of appendages was significantly lower following RNAi treatment than the negative control group, and comparable with the blank control group, further confirming the decrease in Dsx1 expression after RNAi treatment. The number of offspring in all experimental groups was measured, and was significantly greater in the RNAi-treated group compared with the control group. These results provide a foundation for further work on the molecular basis of switching between the two modes of reproduction in cladocerans. The findings also further increase our understanding of the regulatory effects of Dsx1 in the differing sexes in these crustaceans.