Molecular cloning and expression of Octamer-binding transcription factor (Oct4) in the large yellow croaker, Larimichthys crocea

- A full length cDNA of Lc-Oct4 was cloned, characterized and analyzed from Larimichthys crocea.
- Lc-Oct4 was only expressed strongly in ovary with the highest expression level in 635-dph ovary.
- Lc-Oct4 was expressed in oocytes with the highest level in stage II, III.
- Lc-Oct4 was also expressed in spermatogonium and primary spermatocyte of testis.
- Lc-Oct4 was expressed only in early embryos from 2-cell stage to early-gastrula stage.

Octamer-binding transcription factor 4 (Oct4) is a crucial pluripotent transcription factor in controlling pluripotency of embryonic stem cells (ESCs), formation of primordial germ cells (PGCs), early embryonic development, and gonadal germ cells. To understand the roles of Oct4 in the large yellow croaker (Larimichthys crocea) (Lc-Oct4), the full-length cDNA of Oct4 was cloned and analyzed. Lc-Oct4 includes a 104-bp 5′ untranslated region (UTR), a 567-bp 3′ UTR and a 1431-bp coding region encoding a protein of 476 amino acids (aa) with a predicted molecular mass (Mm) of 52.40 kDa and an isoelectric point (PI) of 6.34. Quantitative real time PCR (qRT-PCR) in tissues showed that Lc-Oct4 was only expressed in ovary. During ovarian development, the expression level in 635 days post hatching (635-dph) ovary was about 6.3-fold higher than in 270-dph and 1000-dph ovary. The in situ hybridization analysis showed that Lc-Oct4 had a high expression in the different developmental stages of oocytes with the highest level in stages II (later) and III oocytes. Lc-Oct4 was also expressed in spermatogonia and primary spermatocytes. Furthermore, the qRT-PCR analysis of Lc-Oct4 in different developmental embryos revealed that the expression from high to low was multiple-cell stage > mid-blastula stage = mid-gastrula stage, and the expression in multiple-cell stage was at less 1.6-fold higher than in other stages. Accordingly, the whole mount in situ hybridization (WISH) in embryos demonstrated that Lc-Oct4 was expressed only in early embryonic development from 2-cell stage to early-gastrula stage with the peak at 16-cell stage, but not detected in PGCs area. In conclusion, Lc-Oct4 participated in the oogenesis and early embryonic development in large yellow croaker. Overall, this study provided better understanding of Lc-Oct4 gene and lay the foundation for its function research in the large yellow croaker.