Effect of ENU (ethylnitrosourea) mutagenesis in cleft lip and/or palate pathogenesis in mice

The etiopathogenesis of cleft lip and cleft palate: usefulness and caveats of mouse models

Cleft lip and cleft palate are frequent human congenital malformations with a complex multifactorial etiology. These orofacial clefts can occur as part of a syndrome involving multiple organs or as isolated clefts without other detectable defects. Both forms of clefting constitute a heavy burden to the affected individuals and their next of kin. Human and mouse facial traits are utterly dissimilar. However, embryonic development of the lip and palate are strikingly similar in both species, making the mouse a model of choice to study their normal and abnormal development. Human epidemiological and genetic studies are clearly important for understanding the etiology of lip and palate clefting. However, our current knowledge about the etiopathogenesis of these malformations has mainly been gathered throughout the years from mouse models, including those with mutagen-, teratogen- and targeted mutation-induced clefts as well as from mice with spontaneous clefts. This review provides a comprehensive description of the numerous mouse models for cleft lip and/or cleft palate. Despite a few weak points, these models have revealed a high order of molecular complexity as well as the stringent spatiotemporal regulations and interactions between key factors which govern the development of these orofacial structures.

Cleft lip and palate in mice treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin: a morphological in vivo study

It is well-known that TCDD (2,3,7,8, tetrachloridedibenzo-p-dioxin) induces cleft palates (CPs) in pregnant C57BL mice. However, it is unclear if TCDD is a possible teratogen for cleft lip. We examined maxillofacial malformations including cleft lip in three animal strains: A/J mice, C57BL/6J mice and ICR mice. The A/J mouse develops cleft lip and palate spontaneously at a 5-10% rate. TCDD was administered in olive oil on gestation day (GD) 12.5 with gastric tubes at 10 microg/kg, 20 microg/kg, or 40 microg/kg to examine the dose-response, and on a single day from GD 8.5-14.5 to examine the timing effects of TCDD administration on lip and palate formation. Furthermore, the palatal shelf movements during GD 8.5-14.5 were observed with a stereoscopic microscope. All embryos had cleft palates when the TCDD was administered just before palatogenesis (GD11.5-GD12.5). With respect to the TCDD effects, there were large differences among the strains. In the A/J mice, the difference between a lethal dose and a dose that could induce a cleft palate was close. Cleft lips were not induced, even when the TCDD was given just before labiogenesis. Morphologically, both palatal shelves contacted perfectly along their lengths, but separated and formed cleft palates. In conclusion, TCDD is a strong inducer of cleft palates, and interferes with the fusion phase of the secondary palate, but has no effect on the lip.

Orofacial clefting: recent insights into a complex trait

Orofacial clefts are common birth defects of multifactorial etiology. Several novel approaches have recently been applied to investigate the causes of clefts. These include examining Mendelian forms of clefting to identify genes that might also be implicated in isolated clefting, analyzing chromosomal rearrangements in which clefting is part of the resultant phenotype, studying animal models in which clefts arise either spontaneously or as a result of mutagenesis experiments, exploring how expression patterns correlate with gene function and examining the effects of gene-environment interactions. Together, these complementary strategies are providing researchers with new clues as to what mechanisms underlie orofacial clefting.