A unique 15-bp InDel in the first intron of BMPR1B regulates its expression in Taihu pigs

Background BMPR1B (Bone morphogenetic protein receptor type-1B) is a receptor in the bone morphogenetic protein (BMP) family and has been identified as a candidate gene for reproductive traits in pigs. Our previous study in Taihu pigs found a specific estrogen response element (ERE) in the first intron of the BMPR1B gene that is associated with the number born alive trait. However, little is known about the mechanism by which the ERE regulates the expression of BMPR1B in the endometrium. Results Here, a 15-bp InDel (insertion/deletion) (AGCCAGAAAGGAGGA) was identified as a unique variation in Taihu pigs, and was shown to be responsible for the binding of the type I receptor of estrogen (ESR1) to the ERE using dual-luciferase assays. Four BMPR1B transcripts (T1, T2, T3, and T4) were identified by 5′ RACE in endometrial tissue. Expression of T3 and T4 in the endometrium of Meishan pigs was significantly higher than in Duroc pigs during pregnancy. Luciferase assays showed that three distinct BMPR1B promoters may drive expression of T1, T3, and T4. Interestingly, ERE-mediated enhancement of T4 promoter activity significantly increased expression of Transcript T4 in the endometrium of Taihu pigs ( P < 0.05). In contrast, the ERE inhibited activity of the T3 promoter and decreased expression of the T3 transcript in the Duroc background ( P < 0.05). In summary, we identified a 15-bp InDel in the Taihu ERE that can be used as a molecular marker for the number born alive trait, characterized the 5′ untranslated regions (UTRs) of BMPR1B transcripts in the endometrium, and determined how the transcripts are processed by alternative splicing events. Conclusions Our results provide a foundation for understanding the transcriptional regulation of BMPR1B and its contributions to the unique breeding prolificacy characteristics of Taihu pigs.