Expression of Ovine Membrane Progesterone Receptors (Alpha, Beta, and Gamma) During Early Pregnancy: Implications in Conceptus Growth and Development.

Abstract

Progesterone is indisputably required for establishment and maintenance of pregnancy in all mammals and thought to exert its effects on the developing conceptus indirectly, via the endometrium. However, increasing evidence of steroids directly influencing conceptus development exists. Progesterone can elicit effects through the classical nuclear progesterone receptors as well as membrane progesterone receptors (MPRα, MPRβ, and MPRγ). The temporal changes in gene expression for MPRα, MPRβ, and MPRγ in pregnant compared to cyclic ewes are currently unknown. Because progesterone plays such an important role in maternal support of conceptus (embryo/fetus and associated membranes) survival and development, we hypothesized that expression of the MPRs in uterine endometrium, corpus luteum (CL), and conceptus would increase during early pregnancy in ewes. The objective of the current study was to determine if mRNA for MPRα, MPRβ, and MPRγ was differentially expressed using Real-Time PCR (qPCR) in endometrium and CL from pregnant and cyclic ewes and concepti during early pregnancy (< 30 Days after mating). Differences described are P < 0.05. In the endometrium, all MPRs were expressed on all days evaluated (Days 12-15 and Day 35 and 50). MPRα expression increased in parallel with increasing day of the estrous cycle, with the greatest expression on Days 14 and 15 compared to pregnancy. Interestingly, in endometrium from pregnant ewes, MPRα mRNA decreased with advancing gestation and by Day 50 exhibited the lowest expression compared to all days tested. MPRγ displayed a dramatic increase on Day 35 in the endometrium compared to earlier days examined. In CL from pregnant ewes, MPRα mRNA exhibited the greatest expression compared to MPRβ and MPRγ and a prominent increase in MPRα was noted by Days 35 and 50. Expression of mRNA for MPRα and MPRγ in sheep concepti displayed a similar expression pattern across days tested with greater levels on Days 21 and 30 compared to earlier days collected. Conversely, gene expression of MPRβ in ovine concepti displayed an opposite expression pattern, with the highest levels observed on Day 13 followed by declining expression with increasing age of concepti until Day 30. The increase in MPRα and MPRγ in trophoblast cells from Day 17-21 of pregnancy is intriguing as this correlates with time of apposition of trophoblast cells with luminal epithelium of the endometrium where adhesion complexes are formed by Day 21. Both MPRα and MPRγ remain elevated on Day 30 of gestation, a time during which placentation occurs in sheep. Further, greater expression of MPRβ in trophoblast cells on Day 13 with sequential decreased expression with advancing age of concepti correlates with initial stages of maternal recognition of pregnancy. In summary, ovine concepti express mRNA for MPRα, MPRβ, and MPRγ during the periods of maternal recognition of pregnancy, concepti elongation, apposition, and attachment to endometrium. From these data, it is plausible that progesterone affects concepti survival, growth and development directly in addition to maternal support. Supported by USDA-NIFA-NRI grants 2009-65203-05717, 2006-35203-17258 and 2005-35203-15885. (poster)