Fig. 4

BMP signaling is active in epithelial and basiepithelial cells of the neuro-muscular mesentery. Immunostaining for pSMAD1/5 (cyan), Tyr-tubulin (gray), and DNA (magenta). A Schematic overview of a mesentery cross-section illustrating its morphological domains. Basal mesentery regions are highlighted in color. Images on B–E are transverse sections corresponding to regions boxed on A. F–G’ are high magnification views of areas boxed on E. B–B’ pSMAD1/5-negative body wall gastrodermis and epidermis. C–C’ pSMAD1/5-positive epithelial cell clusters (blue arrowheads) and individual basiepithelial cells (yellow arrowheads). D–D’ pSMAD1/5-positive and -negative cells in the epithelium and the mesoglea of the mesentery stalk (yellow arrowheads). E Cross-section of the retractor muscle region with pSMAD1/5-positive and pSMAD1/5-negative epithelial and basiepithelial cells, retractor muscle myonemes are highlighted in mauve. F’–F” Magnified view of the retractor muscle region epithelium with pSMAD1/5-positive and -negative gastrodermal cells. G’–G” A region of the retractor muscle with pSMAD1/5-positive and -negative epithelial and basiepithelial cells. All stainings were performed at least two times independently with 3 or more animals imaged. Scale bars 25 µm. mg—mesoglea, bwe—body wall epidermis, bwg—body wall gastrodermis, gd—gastrodermis, rm—retractor muscle