Characterization of the distal-less homologue gene, PfDlx, involved in regulating the expression of Pif in the pearl oyster, Pinctada fucata

Distal-less (Dlx) homeobox transcription factors play an important role in regulating various aspects of vertebrate biology. In vertebrates and invertebrates, distal-less is a highly conserved and well-studied transcription factor. In pearl oyster, we have identified a homologue of this gene, Dlx, and cloned the full-length cDNA. Genomic structure analysis revealed that PfDlx genomic DNA contained three exons and two introns. Their deduced amino acid sequences all showed the highest identity with homologues in Crassostrea gigas. Analyses of PfDlx mRNA in tissues and developmental stages showed high expressions in gonad, polar body stage, 2-4 cells and 32 cells. After shell notching, the changes in expression of Dlx shows that it reached a maximum at 24 h. In co-transfection experiments, PfDlx significantly activates reporter constructs containing a Pif promoter. Through using RNAi techniques, we demonstrated that down-regulation of Dlx in P. fucata did not significantly disrupt the development of the nacreous layer in scanning electron microscopy, but it significantly down-regulated the expression of Pif gene. Thus, our work suggests that PfDlx might participate in regulating the expression of the Pif gene in the pearl oyster.