Fig. 2

Epidermal BMP signaling is confined to the oral epithelium. Characterization of BMP signaling in the oral region by anti-pSMAD1/5 staining (cyan). DNA is stained with DAPI (magenta), outlines of tissue layers (solid white lines) and mesoglea (dotted white lines) are indicated. A Mouth region (black box), cross-section of the body column at the pharynx level (red box), B pSMAD1/5 staining in the region of the hypostome, C longitudinal section of the tentacle and tentacle base, D,E details of the tentacle base, F schematic of a cross-section at the pharynx level, G overview of a pharynx cross-section, H mCherry expression in the bmp2/4::mCh reporter line highlights the ciliated groove (siphonoglyph) on one side of the pharynx, I detail of a pharynx cross-section, pSMAD1/5-positive cells are located in the epidermis at the position of the mesentery attachment site (blue arrowhead), J schematic of the mesentery attachment site, K–K’ pSMAD1/5-positive nuclei in the epidermis of the mesentery attachment site at the level of the pharynx and subpharynx, L–L’ BMP signaling is absent in the respective regions at the level of the gonad, trophic, or physa region, M epidermal gremlin expression. mo—mouth, te—tentacle, itr—inter-tentacular region, tb—tentacle base, tb-ep tentacle base epidermis, tb-gd—tentacle base gastrodermis, pha—pharynx, si—siphonoglyph, mes—mesentery, mg—mesoglea, bwe—body wall epidermis, bwg—body wall gastrodermis. All stainings were performed at least two times independently with 3 or more animals imaged. Scale bars 50 µm (white), 25 µm (yellow), and 100 µm (purple)