Mesenchymal SLMAP coordinates with MST3 to govern gut elongation during development

Developing gut in mice undergoes rapid elongation during late embryogenesis, yet significantly slows down after birth. The precise regulatory mechanism of this dynamic morphogenetic process remains unknown. By utilizing single-cell RNA-sequencing analysis, we show that YAP activity in intestinal fibroblasts is the major molecular contributor to gut elongation. To determine how mesenchymal YAP activity is controlled, we identified canonical sarcolemma membrane-associated protein (SLMAP) as its critical regulator during mouse embryonic gut morphogenesis. Deleting Slmap in gut mesenchyme impairs YAP activity, leading to a short gut and a significant decrease in intestinal epithelial cell proliferation. Mechanistically, SLMAP activates YAP by directly regulating MST3 kinase. Physiologically, MST3 levels prominently increase over the developmental time, reaching their peak on postnatal day (P)14, when gut elongation in mice slows down. Depleting Mst3 in mesenchyme results in increased gut length at P14 accompanied by enhanced YAP activity. Importantly, a short gut phenotype in mesenchyme-specific Slmap mutant mice is partially compensated for by concomitant deletion of mesenchymal Mst3. Taken together, our findings demonstrate that SLMAP interacts with MST3 kinase to regulate the mesenchymal YAP activity that governs dynamic gut elongation across embryonic and postnatal development.