Temporal and spatial localization patterns of Gata4 during porcine gonadogenesis.

The zinc finger transcription factor Gata4, is associated with gonadal development in many species. The present study characterizes temporal and spatial localization of Gata4 throughout gonadogenesis in porcine embryos. Immunohistochemical studies illustrated that Gata4 protein is present in the coelomic epithelium prior to histological differentiation of the nascent bipotential gonad, marking the future site of both XX and XY porcine gonads. Many somatic cells of both XX and XY bipotential gonads continue to retain Gata4 immunoreactivity throughout sexual differentiation and subsequent gonadal development. Testicular cords were evident by 26 days postcoitum. Gata4 was present in Sertoli cells, identified by virtue of coexpression with Müllerian inhibiting substance and also interstitial cells including Leydig cells throughout fetal and postnatal life. Many somatic cells of the differentiating ovary including follicular cells also contained Gata4 protein throughout fetal and postnatal life. Gata4 was not present in germ cells, endothelial cells, or other undifferentiated mesenchymal cells of both XX and XY gonads. A population of Gata4-positive cells in the dorsal mesentery was continuous with the coelomic epithelium of the gonad. This localization pattern led to the hypothesis that a subpopulation of somatic cells in the dorsal mesentery moves toward the gonad. An in vitro cell migration assay demonstrated that Gata4-positive cells preferentially migrate toward explanted gonadal tissue, and morphological features of the developing gonad supported this hypothesis. This study illustrates that Gata4 is a very early marker for gonad formation, highlights species differences in temporal and spatial localization patterns, and suggests a potential role for Gata4 in the development of both XX and XY porcine gonads. Further, we suggest that mesenchymal cells of the dorsal mesentery may provide a source of somatic cells that migrate and incorporate into the gonad and contribute to various somatic cell lineages. Overall, the spatial and temporal localization patterns of Gata4 during porcine gonadogenesis implies a much earlier and wider role for Gata4 than previously reported in other species.