Tbx1 is necessary for palatal elongation and elevation

Abstract

The transcription factor TBX1 is a key mediator of developmental abnormalities associated with DiGeorge/Velocardiofacial Syndrome. Studies in mice have demonstrated that decreased dosage of Tbx1 results in defects in pharyngeal arch, cardiovascular, and craniofacial development. The role of Tbx1 in cardiac development has been intensely studied; however, its role in palatal development is poorly understood. By studying the Tbx1-/- mice we found defects during the critical points of palate elongation and elevation. The intrinsic palate defects in the Tbx1-/- mice were determined by measuring changes in palate shelf length, proliferation, apoptosis, expression of relevant growth factors, and in palate fusion assays. Tbx1-/- embryos exhibit cleft palate with failed palate elevation in 100% and abnormal palatal-oral fusions in 50%. In the Tbx1-/- mice the palate shelf length was reduced and tongue height was greater, demonstrating a physical impediment to palate elevation and apposition. In vitro palate fusion assays demonstrate that Tbx1-/- palate shelves are capable of fusion but a roller culture assay showed that the null palatal shelves were unable to elongate. Diminished hyaluronic acid production in the Tbx1-/- palate shelves may explain failed palate shelf elevation. In addition, cell proliferation and apoptosis were perturbed in Tbx1-/- palates. A sharp decrease of Fgf8 expression was detected in the Tbx1-/- palate shelves, suggesting that Fgf8 is dependent on Tbx1 in the palate. Fgf10 is also up-regulated in the Tbx1-/- palate shelves and tongue. These data demonstrate that Tbx1 is a critical transcription factor that guides palatal elongation and elevation and that Fgf8 expression in the palate is Tbx1-dependent.

The regulation of endogenous retinoic acid level through CYP26B1 is required for elevation of palatal shelves

“…The discrepancy between the studies by Goudy et al (2010) and ours may be explained by: (1) the use of different mouse strains, (2) other data were obtained on the anterior palate (Fig. 6 C, D in Goudy et al, 2010), while we focused on the middle palate. Further analyses should be designed to determine whether RA signaling regulates Fgf10 directly or through secondary mediators in the developing palate.…”

“…Fgf10 was upregulated in the entire palatal shelves of Tbx1À/À mice (Goudy et al, 2010). The discrepancy between the studies by Goudy et al (2010) and ours may be explained by: (1) the use of different mouse strains, (2) other data were obtained on the anterior palate (Fig.…”

“…Based on that background, we addressed the question of whether the loss of Fgf10 in the bend region in the absence of Cyp26b1 is via down-regulation of Tbx1 by analysing Tbx1À/À mice. Tbx1À/À mice exhibit cleft palate due to the failure of elevation of the palatal shelves (Goudy et al, 2010). In Tbx1À/À fetuses, Fgf10 expression was maintained in the bend region of palatal shelves (Fig.…”

“…Alternatively, Fgf10 may be regulated indirectly by RA signaling. Recently, Goudy et al (2010) demonstrated that the palatal shelves remain unelevated in Tbx1À/À mice, resulting in cleft palate. Tbx1 has been shown to be a major candidate gene for the DiGeorge syndrome phenotypes, which is characterized by aortic arch anomalies, dysmorphic face, and hypoplasia of the thymus (Baldini, 2005).…”

“…The evaluation of E14.5 tongue height was as described by Goudy et al (2010). An unpaired t-test (two-tail) was used to assess the significance of the data.…”