Maternal inheritance of Nanog ortholog in blunt-snout bream

The homeodomain transcription factor Nanog plays an essential role in maintaining pluripotency and self-renewal of embryonic stem cells in mammals. However, the evolutionary conservation of its ortholog in teleosts remains elusive. Here we isolated and characterized a Nanog homolog named as Ma-Nanog in blunt-snout bream (Megalobrama amblycephala). The full-length genomic sequence is 3,326 bp in length and consists of four exons encoding a homeodomain protein of 386 amino acid residues. Comparison of protein sequences revealed that Ma-Nanog is highly homologous to those in other teleosts, particularly in the homeodomain region. During embryogenesis, RNA expression of Nanog was only detected in early developmental embryos, predominantly at the blastula stage, which suggested the transcripts were mainly present in pluripotent stem cells. RNA fluorescence in situ hybridization verified that the signal of the transcripts is present in the germ cells. RNA expression was observed in the oogonia and early stage of oocytes in the ovary, or in the spermatogonia, spermatocytes, and spermatids in the testis. Surprisingly, the transcripts were also detected in adult tissues such as in liver by RT-PCR or qRT-PCR. Subcellular localization of the Nanog protein was also verified in nuclei. Taken together, these results suggested that Ma-Nanog is maternally inherited with conserved features, thus can be potentially used as a marker for stem cells in blunt-snout bream.