Abstract:This research focuses on the expression characteristics and mechanism of the novel membrane progestin receptor-like (mPR-Like, mPRL) gene of half-smooth tongue sole (Cynoglossus semilaevis) to improve the technique of artificial breeding. In the present study, using the quantitative real-time PCR (qRT-PCR) assays, the mPRL mRNA expression levels were measured in the isolated oocytes during different stages of oogenesis. With the oocyte development, the mPRL transcript levels of oocytes significantly increased from stage Ⅱ to stage Ⅴ and reached the peak at stage Ⅴ. The spatial expression of mPRL mRNA in the ovary, pituitary and brain of C. semilaevis was demonstrated using in situ hybridization. Results revealed that the mPRL expression was observed on the membrane of oocytes, and the positive signals were also observed in the scattered cells throughout the pituitary and in the brain neurons. Western blotting analysis identified the immunoactive protein that bands in the ovary, brain, pituitary, liver, head kidney and kidney of C. semilaevis. However, the expression levels of the protein in the ovary, brain and pituitary were higher than other tissues. Immunohistochemistry detection revealed that the cellular localization of mPRL protein was similar with that of mRNA in C. semilaevis. The signals were observed in the scattered cells of pituitary and the brain neurons. The intensity of the positive signals was found in the membrane of oocyte. After incubation in vitro in the presence or absence of hCG, the mPRL mRNA and protein levels were measured in the oocytes at different developmental stages using qRT-PCR and western blotting analysis. In response to the hCG treatment, the mPRL mRNA and protein expression increased in a step-wise manner during follicle development, with the highest level detected in the stage V of oocytes. The mPRL expression characteristics at both transcript and protein levels implied that mPRL was involved in regulating the reproduction of female C. semilaevis through the brain-pituitary-ovary axis endocrine system. Moreover, the evidence supports that mPRL has a functional role in the oocyte maturation in C. semilaevis by acting as a mediator of progesterone.
