Ruiz Demoulin, S.; Falco, A.; Chauvet, N.; DE SANTA BARBARA, P.; Faure, S.

Gastrointestinal (GI) motility depends on smooth muscle contractions to propel contents through the digestive tract. GI muscle is organized into two perpendicular layers: the inner circular smooth muscle (CSM) and the outer longitudinal smooth muscle (LSM) layers. This organization is important for proper motility. Despite several investigations, GI smooth muscle development remains poorly understood due to several limitations. Previous studies mainly relied on SMA detection in tissue sections and focused on a single organ or developmental stage. They often overlooked key smooth muscle markers such as CALPONIN and {gamma}SMA and largely neglected the LSM layer. In this study, we combined confocal imaging of whole-mount three-dimensional-cleared embryonic chick guts with heatmap analysis to generate the first spatial atlas of smooth muscle development. We characterize the expression patterns of SMA, {gamma}SMA, and CALPONIN1, thereby mapping the dynamics of the formation and differentiation of CSM and LSM layers along the antero-posterior axis. This study provides a framework for future investigations into the regulatory mechanisms governing smooth muscle patterning and maturation along the GI tract.