成熟诱导激素(DHP)是促进硬骨鱼类配子成熟和排卵（精）的孕激素。我们发现DHP合成酶和DHP核受体（PGR）在罗非鱼性别决定和分化早期（孵化后5-20天）的性腺呈现雌性特异表达。PGR拮抗剂(RU486)处理（孵化后5-20天），能够抑制雌激素合成酶基因的表达和雌激素合成，导致XX个体性腺性逆转为精巢。我们创新性地提出DHP在鱼类雌性性别分化过程中发挥重要作用的学术思想。本项目拟进一步证实DHP合成酶和PGR在罗非鱼卵巢分化早期的表达水平和细胞类型，检测血清DHP合成水平。通过RU486处理、激素回救、基因敲除和RNA-Seq揭示DHP影响雌激素通路和雌性性别分化的机制。通过PGR抗体的ChIP-Seq和real-time PCR筛选和鉴定PGR的靶基因，构建DHP调控性别分化的分子网络。最终阐明DHP直接，或者通过雌激素间接调控性腺分化过程的分子机制和表观遗传机制。

In teleosts, maturation inducing hormone (DHP) is a progestin to promote gametes maturation and ovulation (spermiation). During the critical period of sex determination/differentiation in tilapia, specific expression of steroidogenic enzymes (Cyp17a2 and 20β-HSD2) for DHP biosynthesis, and DHP nuclear receptor (PGR) was detected in the XX gonad, but not in the XY gonad. Moreover, we also found that treatment of XX fish by RU486 (a PGR antagonist) from 5 to 20 days after hatching (dah) led to the significant repression of cyp19a1a gene expression, decline of estrogen production, and sex reversal. Therefore, we propose, for the first time, that DHP might play a key role in female sex differentiation in fish. In this proposal, we intend to further investigate the expression level and cellular localization of Cyp17a2, 20β-HSD and PGR during the critical period of sex differentiation in fish gonads. Meanwhile, the plasma DHP level during these stages will also be measured. To clarify the molecular and epigenetic mechanisms of DHP on female sex differentiation in fish, a serials of investigations will be carried out. First of all, RU486 treatment of XX tilapia from 5 dah will be performed and sampled at different time points to see the morphological and molecular changes. High throughput sequencing will be carried out to investigate the changes of miRNA and LncRNA during RU486 treatment. Knockout of Cyp17a2, 20β-HSD and PGR gene by CRISPR/Cas9 based transcriptional silencing technology will be accomplished to check the effects on sex differentiation. Simultaneously, rescue assay will be applied to check whether estrogen or DHP is capable of restoring the effects of RU486 treatment or gene knockout on gonadal differentiation. The target genes of PGR will be screened and characterized by ChIP-seq and real-time PCR, and then the molecular network of DHP in the sex differentiation will be constructed. Our final goal is to clarify the molecular and epigenetic mechanisms that DHP regulates fish gonadal sex differentiation directly or indirectly via estrogen.