Steroidogenic factor 1 (NR5A1) is essential for gonadal development. To study the importance of NR5A1 during early gonadal sex differentiation, we generated Sox9-Cre-Nr5a1 conditional knockout (cKO) mice: Sox9-Cre;Nr5a1^flox/flox and Sox9-Cre;Nr5a1^flox/− mice. Double-immunostaining for NR5A1 and AMH revealed silenced NR5A1 in Sertoli cells and reduced AMH⁺ cells in the gonads of XY Sox9-Cre-Nr5a1 cKO mice between embryonic days 12.5 (E12.5) and E14.5. Double-immunostaining for SOX9 and FOXL2 further indicated an early block in Sertoli cells and ectopic granulosa cell differentiation. The number of cells expressing the Leydig cell marker 3βHSD obviously reduced in the gonads of XY Sox9-Cre;Nr5a1^flox/− but not Sox9-Cre;Nr5a1^flox/flox mice at E15.5. The presence of STRA8⁺ cells indicated that germ cells entered meiosis in the gonads of XY Sox9-Cre-Nr5a1 cKO mice. The results of qRT-PCR revealed remarkably reduced and elevated levels of testis and ovary markers, respectively, in the gonads of XY Sox9-Cre-Nr5a1 cKO mice at E12.5‒E13.5. These data suggested that the loss of Nr5a1 abrogates the testicular pathway and induces the ectopic ovarian pathway, resulting in postnatal partial/complete male-to-female gonadal sex reversal. Our findings provide evidence for the critical role of NR5A1 in murine gonadal sex determination in vivo.

Rupture of the basement membrane in fused palate tissue can cause the palate to separate after fusion in mice, leading to the development of cleft palate. Here, we further elucidate the mechanism of palatal separation after palatal fusion in 8–10-week-old ICR female mice. On day 12 of gestation, 40 μg/kg of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), sufficient to cause cleft palate in 100% of mice, was dissolved in 0.4 mL of olive oil containing toluene and administered as a single dose via a gastric tube. Fetal palatine frontal sections were observed by H&E staining, and epithelial cell adhesion factors, apoptosis, and cell proliferation were observed from the anterior to posterior palate. TUNEL-positive cells and Ki67-positive cells were observed around the posterior palatal dissection area of the TCDD-treated group. Moreover, in fetal mice exposed to TCDD, some fetuses exhibited cleft palate dehiscence during fusion. The results suggest that palatal dehiscence may be caused by abnormal cell proliferation in epithelial tissues, decreased intercellular adhesion, and inhibition of mesenchymal cell proliferation. By elucidating the mechanism of cleavage after palatal fusion, this research can contribute to establishing methods for the prevention of cleft palate development.