Cleft palate formation after palatal fusion occurs due to the rupture of epithelial basement membranes

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces cleft palate and hydronephrosis in the mouse embryo. Cleft palate occurs due to failure in palatal grow, but the underlying mechanisms are unclear. We investigated the mechanisms of cleft palate development in TCDD-exposed mouse embryos. We administered olive oil (control group) or TCDD diluted in olive oil (40 μg/kg) via gastric tubes to pregnant mice on gestational day (GD) 12. Embryos of control and TCDD-exposed groups were removed from pregnant mice on GD 14 and GD 15, respectively. One mouse embryo from the control group had anteroposterior palatal fusion. Palatal fusion was observed in three TCDD-exposed mouse embryos. Palates of TCDD-exposed mice fused from the interior to the middle of the palates, while the palates were separated in the posterior region. The middle of the embryonic palatal shelves in TCDD-exposed animals was narrow and split at the fusional position. At this position, palatal and blood cells were dispersed from the palatal tissue and the epithelium was split, with a discontinuous basement membrane. The results suggest that decreased intercellular adhesion or insufficient tissue strength of the palatal shelves may be involved in the development of cleft palate following palatal fusion.