ABL1 and Rectal prolapse: In summary, our studies uncover an important role for non-receptor tyrosine kinase c-Abl in the homeostasis of the muscularis propria of the GI tract, and suggest that c-Abl−/− mouse is a model for megaesophagus and (atypical) rectal prolapse, which are likely caused by increased proliferation of smooth muscle cells.