Expression and localization of Luman/CREB3 in mouse embryos during the pre-implantation period

Luman/CREB3 is a transcription factor that is a member of the cAMP-response-element-binding protein family of basic region-leucine zipper transcription factors. This protein interacts with host cell factor 1, which also associates with the herpes simplex virus protein VP16 to induce the transcription of herpes simplex virus. Currently, the physiological function of Luman/CREB3 in reproductive processes remains unclear. In this study, quantitative real-time PCR and immunofluorescence assays were used to investigate the expression and localization of Luman in mouse oocytes as well as in early embryonic development. Luman protein was detected in the germinal vesicle and metaphase II stage oocytes, and was distributed in the cytoplasm, nucleus, and polar body of the oocyte stage. However, Luman protein and mRNA expression levels were significantly (P < 0.05) increased before activation of the zygotic genome, and expression levels peaked in 4-cell embryos. Expression levels were significantly (P < 0.05) decreased following the 8-cell stage throughout the blastocyst stage. The Luman protein was also distributed in the nucleus and cytoplasm in the early preimplantation embryo and showed enhanced nuclear staining starting from the 2-cell stage embryo up to the 8-cell stage embryo. The differences in the expression and localization of Luman in mouse oocytes and early embryo suggested that Luman plays an important role in oocyte maturation and early embryonic development processes.