Fig. 6

pSMAD1/5 activity, BMP, and BMP receptor expression in the septal filament. A,B Schematics of the mesentery morphology at the level of the gonad region in a lateral view (A) and in a transverse section (B). Sub-regions of the septal filament highlighted in shades of yellow. C–F BMP receptor expression of the type I receptors alk2 (C) and alk3/6 (D), and of the type II receptors actRII (E) and bmprII (F) in the septal filament. G–I’ Immunostaining for pSMAD1/5 (cyan) with DNA counterstained in magenta in the septal filament. G–G’ Cross-section of the mesentery of a male in the gonad region, ciliated tracts are indicated (ct), blue arrowheads highlight pSMAD1/5 in the reticular tract (rt), H–H’ top view of the ciliated tract showing pSMAD1/5 activity in its folds. I–I’ Longitudinal optical section of the ciliated tract showing pSMAD1/5 activity in the folds. J–L bmp2/4 expression in the septal filament in cross-section and lateral views. M–O mCherry expression in the bmp2/4::mCherry reporter line. M–N’ mCherry is expressed in the mesentery gastrodermis and in the ciliated tract of the adult polyp. O–P bmp2/4::mCherry activity in the ciliated tract in the juvenile polyp. Q–T bmp5-8 expression in the mesentery gastrodermis, reticular tract and ciliated tract; cross-section (Q), and lateral views (R-T). All stainings were performed at least two times independently with 3 or more animals imaged. Scale bars 25 µm (white), 50 µm (yellow), and 100 µm (black). ep—epidermis, pm—parietal muscle, rm—retractor muscle, gd—gastrodermis, sp—spermary, rt—reticular tract, ct—ciliated tract, cgt—cnidoglandular tract, sg—somatic gonad