Transcriptional regulation of the membrane progestin receptor α gene PAQR7 underlying progesterone responsiveness in sperm storage tubules of Japanese quail.

In birds, sperm storage tubules (SSTs) located at the uterovaginal junction (UVJ) facilitate long-term sperm storage and regulate sperm release in coordination with ovulation. In Japanese quail (Coturnix japonica), sperm release from SSTs might be mediated by membrane progestin receptor α (mPRα), encoded by the progestin and adipoQ receptor family member 7 (PAQR7) gene. Although PAQR7 plays an important role in reproductive functions, the mechanisms regulating its transcription remain unclear. Therefore, in this study, we investigated the transcriptional regulatory mechanisms of PAQR7 in Japanese quail SSTs. Reporter assays using serial deletion constructs identified multiple positive and negative regulatory regions within the 5' upstream region of PAQR7. Analysis of the proximal promoter region revealed a putative initiator element and non-canonical promoter structure. Electrophoretic mobility shift assays identified several nuclear protein-binding regions within the upstream regulatory region. Candidate transcription factors potentially binding to these regions were predicted using JASPAR and RNA-Seq transcriptome data. Quantitative PCR further revealed that FOS, JUN, FOXN1, and SOX17 levels were significantly upregulated in SST-containing tissues compared to those in non-SST epithelial tissues. Overall, our findings suggest that PAQR7 expression in SSTs is regulated by an SST-specific transcriptional environment involving activator protein-1 (AP-1; FOS-JUN complex), JUN, FOXN1, and SOX17. These findings provide new insights into the transcriptional regulation of progesterone responsiveness in avian reproductive tissues and advance our understanding of endocrine mechanisms underlying sperm storage.