Expression and regulation of inhibitor of DNA binding proteins ID1, ID2, ID3, and ID4 at the maternal-conceptus interface in pigs.

Inhibitor of DNA binding (ID) proteins, ID1, ID2, ID3, and ID4 are transcriptional regulators that have a helix-loop-helix (HLH) domain but not a basic DNA binding domain. ID proteins inhibit the functions of basic HLH transcription factors and regulate cell proliferation and differentiation. However, the expression and function of ID1, ID2, ID3, and ID4 at the maternal-conceptus interface are not fully understood in pigs. Therefore, we determined the expressions of ID1, ID2, ID3, and ID4 in porcine endometrium, conceptus, and chorioallantoic tissues. ID1, ID2, ID3, and ID4 mRNAs were expressed in the endometrium, with lower levels of ID1, ID2, and ID4 on Day 12 of pregnancy than during the estrous cycle. ID1, ID2, ID3, and ID4 mRNAs were also detected in conceptus and chorioallantoic tissues during pregnancy. ID2 protein was mainly localized to luminal epithelia and weakly to vascular smooth muscle cells in the endometrium and conceptus trophectoderm. Increasing doses of interleukin-1β decreased levels of ID2 mRNA, while estradiol-17β increased levels of ID3 mRNA in endometrial explants. The expressions of ID2 and ID4 mRNAs were higher in endometria from gilts with somatic cell nuclear transfer-derived conceptuses compared with endometria from gilts carrying conceptuses derived from natural mating on Day 12. These results indicate that the expressions of ID family genes are dynamically regulated at the maternal-conceptus interface, suggesting that ID proteins may play critical roles in the regulation of endometrial epithelial cell function and conceptus development to support the establishment and maintenance of pregnancy in pigs.