Essential role for complex N-glycans in forming an organized layer of bronchial epithelium

Mice lacking the complex subset of N-glycans due to inactivation of the Mgat1 gene die at mid-gestation, making it difficult to identify specific biological functions for this class of cell surface carbohydrates, To circumvent this embryonic lethality and to uncover tissue-specific functions for complex N-glycans, WW6 embryonic stem cells with inactivated Mgat1 alleles were tracked in chimeric embryos, The Mgat1 gene encodes N-acetylglucosaminyltransferase I (GlcNAc-TI; EC 2.4.1.101), the transferase that initiates the synthesis of complex N-glycans, WW6 cells carry an inert beta-globin transgene that allows their identification in chimeras by DNA-DNA in situ hybridization, Independent Mgat1(-/-) and Mgat1(+/-) mutant WW6 isolates contributed like parent WW6 cells to the tissues of embryonic day (E) 10.5 to E16.5 chimeras, However, a cell type-specific difference was observed in lung, Homozygous null Mgat1(-/-) WW6 cells did not contribute to the epithelial layer in more than 99% bronchi, This deficiency was corrected by transfection of a Mgat1 transgene, Interestingly, heterozygous Mgat1(+/-) WW6 cells were also deficient in populating the layer of bronchial epithelium. Furthermore, examination of lung bud in E9.5 Mgat1(-/-) mutant embryos showed complete absence of an organized epithelial cell layer in the bronchus, Thus, complex N-glycans are required to form a morphologically recognizable bronchial epithelium, revealing an in vivo, cell type-specific function for this class of N-glycans.