Tissue-Specific Roles for the Slit-Robo Pathway During Heart, Caval Vein, and Diaphragm Development.

Background Binding of Slit ligands to their Robo receptors regulates signaling pathways that are important for heart development. Genetic variants in and have been linked to congenital heart defects in humans. These defects are recapitulated in mouse models with ubiquitous deletions of the Slit ligands or Robo receptors and include additional heart defects not currently linked to SLIT or ROBO mutations in humans. Given the broad expression patterns of these genes, the question remains open which tissue-specific ligand-receptor interactions are important for the correct development of different cardiac structures. Methods and Results We used tissue-specific knockout mouse models of /, , and and scored cardiac developmental defects in perinatal mice. Knockout of in either the whole heart, endocardium and its derivatives, or the neural crest in ubiquitous knockout background resulted in ventricular septal defects. Neural crest-specific removal of in knockouts showed fully penetrant bicuspid aortic valves (BAV). Endocardial knock-out of either or caused low penetrant BAV. In contrast, endocardial knockout of using a newly generated line resulted in fully penetrant BAV, while removal from smooth muscle cells also resulted in BAV. Caval vein and diaphragm defects observed in ubiquitous mutants were recapitulated in the tissue-specific knockouts. Conclusions Our data will help understand defects observed in patients with variants in and . The results strongly indicate interaction between endocardial and neural crest in the development of BAV, highlighting the need for further studies of this connection.