Fig. 10. Model for the activity of ElB in the trachea. Noc is an essential partner in the dimer. It is broadly expressed and thus does not give rise to a phenotype upon overexpression. Conversely, elB expression in the trachea is restricted to the dorsal branch and lateral trunks from stage 12 (red). This restricted expression is crucial for the correct determination of branch-specific cell fates. Overexpression of ElB represses the expression of genes in the visceral branch (VB) and dorsal trunk (arrows), while elB mutant embryos exhibit defects in the migration of the lateral trunks and dorsal branch (arrows). We suggest that normally ElB/Noc repress transcription of visceral-branch genes in the lateral trunks, and dorsal-trunk genes in the dorsal branch, thus contributing to the definition of branch-specific cell fates. Subsequently, ElB expression is refined to the fusion cells of the dorsal branch, where ElB/Noc are required for repression of terminal cell markers.

Return to article