The Divergent and Conserved Expression Profile of Turtle Nanog Gene Comparing with Fish and Mammals

Simple Summary Chinese soft-shell turtle (Pelidiscus sinensis) is a widely farmed aquatic reptile in China. It has of high nutritional, pharmaceutical, and economic value, but wild Chinese soft-shell turtle has been faced with an extreme decline of populations. Thus, it is of great significance to study the germ cells biology and develop the techniques for turtle breeding and genetic resource preserving. Nanog is a homeodomain-containing transcription factor, and it plays a vital role in maintaining the pluripotency of embryonic stem cells; there is a lack of reporting on the Nanog gene in reptile. In this study, the cDNA sequence and promoter of a Nanog gene was identified in P. sinensis, designed as PsNanog. PsNanog gene products were mainly expressed in gonads and were especially rich in ovary. Particularly, PsNanog mRNA and protein was exclusively expressed in germ cells in ovary and testis. Collectively, this is the first report on the gene structure and expression of Nanog in turtle, which may lay a foundation for further functional analysis of the Nanog in turtle, even in the reptiles. Further, PsNanog probably has the conserved and divergent function in regulating cell pluripotency and germ cell development in turtle, compared with other species, including teleosts and mammals. Nanog is a homeodomain-containing transcription factor, and it plays a vital role in maintaining the pluripotency of embryonic stem cells. Nanog's function has been well studied in many species. However, there is lack of reporting on the Nanog gene in reptile. Here, we identified a 1032 bp cDNA sequence of a Nanog gene in Pelidiscus sinensis, known as PsNanog. PsNanog has a highly conserved HD domain and shares a high identity with that of Chelonia mydas and the lowest identity with Oryzias latipes. Similarly, PsNanog presented a tight cluster with C. mydas Nanog, but was far from those of teleosts. Additionally, we cloned a length of 1870 bp PsNanog promoter. Dual luciferase assay showed that the DNA fragment of -1560 to +1 exhibited a high promoter activity. The RT-PCR and RT-qPCR results showed that PsNanog was predominantly expressed in ovary, and then in testis. The in situ hybridization and immunohistochemical analysis showed that PsNanog was expressed in the early primary oocytes and the cytoplasm of the cortical region of stage VIII oocytes in ovary, and distributed in most stages of germ cells in testis. Collectively, the results imply that PsNanog probably has the conserved function in regulating germ cell development across phyla and is also a pluripotent cell gene and expressed in germ cells, which is similar to that in teleosts and mammals.