Molecular characterization and expression of porcine bone morphogenetic protein receptor-IB in the uterus of cyclic and pregnant gilts

Previous gene mapping analyses revealed a quantitative trait locus for uterine capacity on chromosome 8. Comparison of porcine and human genetic maps suggests that the bone morphogenetic protein receptor IB (BMPR-IB) gene may be located near this region. The objectives of this study were to 1) clone the full coding region for BMPR-IB, 2) examine BMPR-IB gene expression by the endometrium and its cellular localization in cyclic and pregnant gilts, and 3) map the BMPR-IB gene. By iterative screening of an expressed sequence tag library, we obtained a 3559-base pair cDNA clone including the full coding region of BMPR-IB. Endometrial BMPR-IB mRNA expression of White composite gilts was determined by Northern blotting in Days 10, 13, and 15 cyclic and Days 10, 13, 15, 20, 30, and 40 pregnant gilts. In cyclic gilts, endometrial BMPR-IB mRNA expression was elevated on Days 13 and 15 (P < 0.01) compared with Day 10. Expression of BMPR-IB mRNA was localized in both luminal and glandular epithelium on Day 15. However, in pregnant gilts, BMPR-IB mRNA expression was not significantly different in the endometrium from Day 10 to Day 20, and it was significantly decreased on Days 30 and 40 (P = 0.011). The BMPR-IB gene was mapped to 108 cM on chromosome 8. These findings show that RMPR-IB mRNA expression is regulated differently in cyclic and pregnant gilts; this pattern of gene expression may be important for endometrial function during the luteal phase of the estrous cycle as compared with early pregnancy.