NKX2.1 is a homeodomain transcriptional factor expressed in thyroid, lung, and parts of the brain. We demonstrate that septation of the anterior foregut along the dorsoventral axis, into distinct tracheal and esophageal structures, is blocked in mouse embryos carrying a homozygous targeted disruption of the Nkx2.1 locus. This is consistent with the loss of Nkx2.1 expression, which defines the dorsoventral boundary within the anterior foregut in wild-type E9 embryos. Failure in septation between the trachea and the esophagus in Nkx2.1(-/-) mice leads to the formation of a common lumen that connects the pharynx to the stomach, serving both as trachea and as esophagus, similar in phenotype to a human pathologic condition termed tracheoesophageal fistula. The main-stem bronchi bifurcate from this common structure and connect to profoundly hypoplastic lungs. The mutant lungs fail to undergo normal branching embryogenesis, consist of highly dilated sacs that are not capable of sustaining normal gas exchange functions, and lead to immediate postnatal death. In situ hybridization suggests reduced Bmp-4 expression in the mutant lung epithelium, providing a possible mechanistic clue for impaired branching. Functional deletion of Nkx2. 1 blocks pulmonary-specific epithelial cell differentiation marked by the absence of pulmonary surfactant protein gene expression. Altered expression of temporally regulated genes such as Vegf demonstrates that the lung in Nkx2.1(-/-) mutant embryos is arrested at early pseudoglandular (E11-E15) stage. These results demonstrate a critical role for Nkx2.1 in morphogenesis of the anterior foregut and the lung as well as in differentiation of pulmonary epithelial cells.

Cleft palate and skull malformations represent some of the most frequent congenital birth defects in the human population. Previous studies have shown that TGFβ signaling regulates the fate of the medial edge epithelium during palatal fusion and postnatal cranial suture closure during skull development. It is not understood, however, what the functional significance of TGFβ signaling is in regulating the fate of cranial neural crest (CNC)cells during craniofacial development. We show that mice with Tgfbr2conditional gene ablation in the CNC have complete cleft secondary palate,calvaria agenesis, and other skull defects with complete phenotype penetrance. Significantly, disruption of the TGFβ signaling does not adversely affect CNC migration. Cleft palate in Tgfbr2 mutant mice results from a cell proliferation defect within the CNC-derived palatal mesenchyme. The midline epithelium of the mutant palatal shelf remains functionally competent to mediate palatal fusion once the palatal shelves are placed in close contact in vitro. Our data suggests that TGFβ IIR plays a crucial, cell-autonomous role in regulating the fate of CNC cells during palatogenesis. During skull development, disruption of TGFβ signaling in the CNC severely impairs cell proliferation in the dura mater, consequently resulting in calvaria agenesis. We provide in vivo evidence that TGFβ signaling within the CNC-derived dura mater provides essential inductive instruction for both the CNC- and mesoderm-derived calvarial bone development. This study demonstrates that TGFβ IIR plays an essential role in the development of the CNC and provides a model for the study of abnormal CNC development.

. Smad3 deficiency attenuates bleomycin-induced pulmonary fibrosis in mice.

No abstract