Examining the spatio-temporal expression of mRNA encoding the membrane-bound progesterone receptor-alpha isoform in human cervix and myometrium during pregnancy and labour

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Abstract
Human parturition is associated with a modification in the sensitivity of the myometrium to progesterone. The molecular basis for this change, however, remains unclear. It is well documented that progesterone can exert its effects through non-genomic mechanisms, including acting through membrane-bound progesterone receptors (mPRs). Recently, a novel membrane-bound PR, termed mPRα, was cloned. mPRα was unlike any other PR in the databases, but it was seen to have significant homology to G-protein-coupled receptors (GPCR). In this study, we examined the spatio-temporal expression of mPRα mRNA in human cervix and both lower and upper myometrial segments from non-pregnant (NP), pregnant (P) and spontaneously labouring (SL) women. We observed an incremental increase in mPRα mRNA expression in NP and P samples with the peak level being observed in SL tissues. No major differences were observed between upper or lower pregnant myometrial regions. Interestingly, levels of mPRα transcripts were substantially greater in labouring lower segment myometrium compared with labouring upper segment. Significantly, we failed to detect mPRα message in either unripe or ripe human cervices. These data suggest that mPRα protein function may play a role in regulating lower segment myometrial activity during labour. Whether it functions in the cervix, however, remains unclear.

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