Preterm birth is the most important complication contributing to poor pregnancy and neonatal outcome. A critical issue that must be resolved is how spontaneous onset labour is initiated both at term and preterm. Over the past decade, we and others have provided evidence in support of the hypothesis that labour onset is regulated by specific nuclear regulatory factor (NR) pathways, involving an interplay between transcription factors (TFs) and nuclear hormone receptors, that control the expression of many of the effector pathways requisite for labour and delivery. There is now compelling evidence implicating NRs, including the nuclear factor-kappaB (NF-kappaB) family of nuclear TFs, the nuclear hormone receptor superfamily of peroxisome proliferator activated receptors (PPARs), and the steroid receptors for progesterone (PRA, PRB and PRC), as candidate upstream regulators of labour-associated processes. Based on these studies and recent data obtained in our laboratory, we provide a new model of how the multiple pathways involved in spontaneous onset labour and delivery are coordinated at a nuclear level. We propose that spontaneous onset labour and delivery are consequent upon withdrawal of the repressive effect of nuclear receptors (PPAR and PR) on pro-labour TF pathways (NF-kappaB). The withdrawal of NR-mediated repression is affected by competition between TFs and NRs for a limited pool of nuclear cofactors. We also propose that coordination of these different pathways is achieved by competition for common cofactors that control the activity of NRs in human gestational tissues.
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