RESULTS: Here, using four separate Cre-lox conditional deletion models, as well as one genetic epistasis approach (Grhl2+/- ;Edn1+/- double heterozygous mice) we have investigated tissue-specific roles of Grhl2 in embryonic development, with a particular focus on the craniofacial skeleton. We find that loss of Grhl2 in the pharyngeal epithelium (using the ShhCre driver) leads to low-penetrance micrognathia, whereas deletion of Grhl2 within the ectoderm of the pharynx (NestinCre ) leads to small, albeit significant, differences in the proximal-distal elongation of both the maxilla and mandible. Loss of Grhl2 in endoderm (Sox17-2aiCre ) resulted in noticeable lung defects and a single instance of secondary palatal clefting, although formation of other endoderm-derived organs such as the stomach, bladder and intestines was not affected. Lastly, deletion of Grhl2 in cells of the neural crest (Wnt1Cre ) did not lead to any discernible defects in craniofacial development, and similarly, our epistasis approach did not detect any phenotypic consequences of loss of a single allele of both Grhl2 and Edn1.
CONCLUSIONS: Taken together, our study identifies a pharyngeal-epithelium intrinsic, non-cell-autonomous role for Grhl2 in the patterning and formation of the craniofacial skeleton, as well as an endoderm-specific role for Grhl2 in the formation and establishment of the mammalian lung.