What knockout mice can tell us about parturition

Many molecules, including steroid and peptide hormones, prostaglandins and cytokines, regulate the preparation, initiation and progression of parturit ion in mammals. Gene targeting studies show that, in the knockout mice of s teroid 5 alpha-reductase type 1 gene, prostaglandin F-2 alpha receptor gene and cytosolic phospholipase A(2) gene, parturition was severely disturbed, although live offspring were delivered by Caesarean section. Relaxin gene- disrupted mice also showed protracted labour. However, most knockout mice i n which the steroid hormone, prostaglandin, cytokine or peptide hormone (fo r example, oxytocin, corticotrophin releasing hormone and endothelin) endoc rine-paracrine systems are disrupted are inadequate for analysis of the mec hanism of parturition because they die before reaching reproductive age or are infertile, or because they reproduce normally. A conditional knockout s trategy, for example, using the Cre-LoxP system, should be considered for i nvestigating the biochemical background of parturition to overcome these pr oblems.