Cloning and characterization of buffalo NANOG gene: alternative transcription start sites, splicing, and polyadenylation in embryonic stem cell-like cells.

NANOG is a critical homeodomain transcription factor responsible for maintaining embryonic stem cell (ESC) self-renewal and pluripotency. In the present study, we isolated, sequenced, and characterized the NANOG gene in buffalo ESC-like cells. Here, we demonstrated that NANOG mRNA is expressed as multiple isoforms and uses four alternative transcriptional start sites (TSSs) and five different polyadenylation sites. The TSSs identified by 5'-RNA ligase-mediated rapid amplification of cDNA ends (RLM-5'-RACE) were positioned at 182, 95, 35, and 17 nucleotides upstream relative to the translation initiation codon. 3'-RACE experiment revealed the presence of tandem polyadenylation signals, which leads to the expression of at least five different 3'-untranslated regions (269, 314, 560, 566, and 829 nucleotides). Expression analysis showed that these alternatively polyadenylated transcripts expressed differentially. Sequence analysis showed that the open reading frame of buffalo NANOG codes for a 300-amino-acid-long protein. Further, results showed that alternative splicing leads to the expression of two types of transcript variants encoded by four and five exons. In silico analysis of cloned 5'-flanking region (3366 nucleotides upstream of translation start codon) identified several putative transcription factors binding sites in addition to a TATA box and CAAT box at -30 and -139 bp (upstream to the distal most TSS), respectively, in the buffalo NANOG promoter.