The novel OCT4 spliced variant OCT4B1 can generate three protein isoforms by alternative splicing into OCT4B

OCT4 is one of the key transcription factors in maintaining the pluripotency and self-renewal of embryonic stem (ES) cells. Human OCT4 can generate two isoforms OCT4A and OCT4B by alternative splicing. OCT4B1 is a recently discovered novel OCT4 spliced variant, which has been considered as a putative marker of stemness. Compared with the OCT4B mRNA, OCT4B1 mRNA is generated by retaining intron 2 as a cryptic exon which contains a TGA stop codon in it. As a result, the protein product of OCT4B1 mRNA could be truncated. Interestingly, we present here that OCT4B1 can indirectly produce the same protein products as OCT4B. We have demonstrated that OCT4B1 mRNA can be spliced into OCT4B mRNA, and encode three protein isoforms. The splicing of OCT4B1 mRNA into OCT4B mRNA can be remarkably inhibited by the mutation of the classical splicing site. Our result suggests that OCT4B mRNA may originate from OCT4B1 mRNA by alternative splicing.