Differentiation of uterine stromal cells is critical for the establishment of pregnancy. This study had two purposes: (i) to validate the use of the UIII rat uterine stromal cell model for investigating mechanisms underlying decidual cell differentiation, and (ii) to use this cell model to identify a molecular switch for cellular entry into the decidual cell differentiation pathway. Quiescent rat uterine stromal cells were transfected with a 500 bp segment of the decidual prolactin-related protein (dPRP) promoter ligated to a luciferase reporter gene. Cells were incubated in low-serum medium, or in low-serum medium containing progesterone (1 μM), estradiol 17-β (10 nM), cholera toxin (10 ng/ml) and interleukin-11 (10 ng/ml). Protein extracts were collected 48 h later and luciferase was measured in the cellular lysates. Cholera toxin and interleukin-11 stimulated luciferase expression (P< 0.05) and addition of sex steroids further increased (P< 0.05) dPRP promoter activity. Stromal cells did not proliferate (P< 0.05) under differentiation conditions. Deletion analysis of the dPRP promoter revealed maximal luciferase expression between −250 and −500 bp relative to the transcription start site. Comparison of cyclin E/Cdk2 activity between proliferating and differentiating cells showed a 3-fold increase (P< 0.05) at 12 h in differentiating cells. The results suggest that cyclin E/Cdk2 serves as a molecular switch for uterine stromal cell entry into the decidual cell differentiation pathway.

Distal-less 3 (Dlx3) is a homeobox factor that functions as a placental-specific transcriptional regulator. Dlx3 null mice (−/−) have compromised placental development and do not survive in utero past embryonic day (E) 9.5. The current studies were undertaken to examine the expression of Dlx3 in mouse placenta during gestation, and to determine whether Dlx3 was involved in placental progesterone production. Dlx3 was not detectable at E8.5 but was detected in E9.5 placenta with continuing but diminished expression through E15.5. Dlx3 immuno-localization was restricted to the labyrinth, was nuclear and was found in cytokeratin-positive cells. Previous studies in choriocarcinoma cell lines support the conclusion that Dlx3 is required for expression of 3′-hydroxysteroid dehydrogenase VI (3βHSD VI), an obligate enzyme in the production of progesterone by trophoblast giant cells. In a rat trophoblast stem cell line (Rcho-1), Dlx3 expression was non-detectable in Rcho-1 cells induced to differ-entiate using mitogen withdrawal. In vitro progesterone production in placental cultures and 3βHSD VI mRNA from Dlx3 (+/+), (+/−) and (−/−) mice were equivalent. In situ hybridization for 3βHSD VI revealed mRNA expression restricted to trophoblast giants cells with no detectable expression in the labyrinth suggesting that Dlx3 and 3βHSD VI were not colocalized within the placenta. These studies support the conclusion that Dlx3 protein expression is restricted to the labyrinth region of the murine placenta into late gestation and that Dlx3 does not appear to be expressed in trophoblast giant cells. Further, loss of Dlx3 was not correlated with synthesis of progesterone from E9.5 mouse placentas.

Mammals share common strategies for regulating reproduction, including a conserved hypothalamic–pituitary–gonadal axis; yet, individual species exhibit differences in reproductive performance. In this report, we describe the discovery of a species-restricted homeostatic control system programming testis growth and function. Prl3c1 is a member of the prolactin gene family and its protein product (PLP-J) was discovered as a uterine cytokine contributing to the establishment of pregnancy. We utilized mouse mutagenesis of Prl3c1 and revealed its involvement in the regulation of the male reproductive axis. The Prl3c1-null male reproductive phenotype was characterized by testiculomegaly and hyperandrogenism. The larger testes in the Prl3c1-null mice were associated with an expansion of the Leydig cell compartment. Prl3c1 locus is a template for two transcripts (Prl3c1 -v1 and Prl3c1-v2) expressed in a tissue-specific pattern. Prl3c1-v1 is expressed in uterine decidua, while Prl3c1-v2 is expressed in Leydig cells of the testis. 5′RACE, chromatin immunoprecipitation and DNA methylation analyses were used to define cell-specific promoter usage and alternative transcript expression. We examined the Prl3c1 locus in five murid rodents and showed that the testicular transcript and encoded protein are the result of a recent retrotransposition event at the Mus musculus Prl3c1 locus. Prl3c1-v1 encodes PLP-J V1 and Prl3c1-v2 encodes PLP-J V2. Each protein exhibits distinct intracellular targeting and actions. PLP-J V2 possesses Leydig cell-static actions consistent with the Prl3c1-null testicular phenotype. Analysis of the biology of the Prl3c1 gene has provided insight into a previously unappreciated homeostatic setpoint control system programming testicular growth and function.