The purpose of this study is to investigate the expression change of cell cycle-related molecules in platal tissue of fetal mice with cleft palate, induced by 2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin (TCDD), and to explore the mechanism of cell cycle-related molecules in cleft palate.

In vivo, 48 pregnant mice were randomly divided into TCDD treatment group and control group with Random number table, 24 mice in each group. On the embryonic day 10.5 (E10.5), pregnant mice were orally administrated with TCDD 28 μg/kg (containing 5 μg/ml TCDD of corn oil) in TCDD treatment group. The same volume of corn oil was given to the mice in control group. The pregnant mice in each group were sacrificed on E13.5, E14.5 and E15.5, to collect the fetal palates for analysis. Fetal palates were used to extract total RNA and total protein, so as to detect the expression levels of cell cycle-related molecules, using RT-PCR and western blotting respectively. In vitro, human kidney embryo 293t (HEK293t) cells were treated with different concentrations of TCDD (0.01, 0.1, 0.5 and 1 nmol/L), and cells proliferation activity was detected using MTT assay. Statistical analysis was performed with IBM SPSS 24.0. Kolmogorov-Smimov test was used for normal distribution check, and the distribution was normal. Independent t-test was carried out among two groups. P<0.05 was considered statistically significant.

At E13.5, E14.5 and E15.5, the expression level of interferon regulatory factor 6 (Irf6) protein were higher in the control group (1.26 ± 0.13, 1.67 ± 0.14 and 1.42 ± 0.15, respectively) compared to that in the TCDD group (0.81 ± 0.08, 1.04± 0.02 and 0.86 ± 0.12, respectively), on each time point (t value were 2.836, 3.662 and 2.867, respectively; P values were 0.0471, 0.0146 and 0.0241, respectively). The expression level of cyclin-dependent kinase inhibitor 1A (P21) protein on E13.5 and E14.5 of the control group (2.26 ± 0.21, 1.99 ± 0.21)were higher than that in the TCDD group on each time point(1.43 ± 0.12、0.93 ± 0.22), (t value were 3.398 and 3.378; P value were 0.8726 and 0.0273). The expression level of cyclin D1 in the control group (1.00±0.02, 0.94±0.03 and 1.11±0.09, respectively)were higher than that of the TCDD group (0.28±0.01, 0.33±0.06 and 0.88±0.01, respectively) on each time point (t value are were 22.53, 22.35 and 14.27, respectively, P value <0.001, <0.001 and<0.001, respectively). The expression of cyclin E1, cyclin A2, cyclin B1, CDK6, CDK2 and CDK1 in TCDD groups were higher than that of the controls (P<0.05). However, there was no significant difference of cyclin B1 on E13.5 and Cdk2 on E15.5. As treatment with TCDD (0.1 nmol/L) at 1, 2 and 3 days (0.70 ± 0.05, 1.05 ± 0.03 and 1.39 ± 0.04, respectively), the proliferation of HEK293t cells increased compared with the control group (0.49 ± 0.04, 0.98 ± 0.03 and 1.55 ± 0.02, respectively). The differences were statistically significant (t value were 2.829, 1.395 and 2.692, respectively; P value were 0.0198, 0.1320 and 0.0247, respectively).

TCDD down-regulates Irf6 and P21, and interferes with the normal expression of cell cycle-associated molecules, which in turn interferes with medial edge epithelia (MEE) cells cycle arrest and proliferation. These indicate that the disorder of spatiotemporal expression of cell cycle-related molecules during palatal development may be involved with the mechanism of TCDD-induced cleft palate..

Cell cycle; 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin; Cleft Palate; Medial edge epithelia