The cloning and expression analysis of dazl in germ cells in the Chinese soft-shelled turtle (Pelodiscus sinensis)

In this study, we used Pelodiscus sinensis as a model to study the germ cells differentiation in reptiles. Firstly, we cloned P. sinensis dazl cDNA fragment of 1 007 bp, containing a 197 bp 5′ untranslated region (UTR), a 33 bp 3′ UTR and an open reading frame (ORF) for 258 amino acid residues. The predicted P. sinensis Dazl was maximally 96% identical with Chrysemys picta bellii Dazl protein, 75% identical with Mus musculus Dazl protein. The RT-PCR result showed that the P. sinensis dazl mRNA was absent in all somatic tissues, but abundant in adult ovary and testis. Chemical in situ hybridization revealed that the P. sinensis dazl mRNA was exclusively expressed in germ cells but barely detected in somatic cells, and displayed a dynamic distribution expression pattern in germ cells during gametogenesis. In adult testis, the dazl mRNA signals were strongly dispersed in primary spermatocyte and secondary spermatocyte, weakly in spermatogonia, barely detected in spermatids. In adult ovary, the dazl mRNA signals were strong in early primary stages of oocytes and displayed a uniform distribution; as oocytes grew into larger size, the dazl mRNA signals were concentrated in the perinuclear cytoplasm and became weak as vitellogenesis further developed. In conclusion, the findings in this study suggested that dazl gene would play important roles in germ cells differentiation during gametogenesis in P. sinensis. The characterization of dazl gene in P. sinensis would provide the basis for further invstigations into reproductive development in turtles or reptiles.