Fig. 6

Arm end-differentiation. (A-A′) oral view of arm crowns at stage 27 labeled with phallacidin to visualize F-actin in green (A) and anti-acetylated tubulin to visualize nerve tracts in red (A′). (B) sagittal histological section of arm II stained with AZAN stain. (B′) confocal image of frontal sections of arm II treated with EdU to visualize proliferating cell nuclei in cyan, merged with a DIC image of the arms in the same focal plane stacks. (C-C′) confocal image stacks of arm II stained for phallacidin to visualize F-actin in green. (D-D′) confocal image stacks of arm II labeled with anti-acetylated tubulin to visualize nerve tracts in red. (E-E′) overlap of musculature and nerve tracts in merged images. (F) sagittal histological section of arm II stained with Toluidine blue. (F′) confocal image of median oral sections of arm IV treated with EdU to visualize proliferating cell nuclei in cyan, merged with a DIC image of the arms in the same focal plane stacks. (G-G′) confocal image stacks of arm IV stained for phallacidin to visualize F-actin in green. (H-H′) confocal image stacks of arm IV labeled with anti-acetylated tubulin to visualize nerve tracts in red. (I-I′) overlap of musculature and nerve tracts in merged images. x marks the position of the mouth, I – V denotes the arm pairs in the order they are spatially positioned. Arms are oriented with aboral to the top and distal to the left. Brackets in (B) show the extend of single ganglia, asterisk marks the axial nerve cord, arrow points at transverse muscle fibers, open arrowhead indicates the longitudinal muscle fibers, arrowhead indicates anastomoses. ch, chromatophore; ci, cilia; co, connective fiber; ep, epithelium; imnc, intramuscular nerve cord; m, muscle; o, oblique musculature; pnc, putative neuronal cells; su, sucker; slm, superficial longitudinal muscle; v, vein. Scale bars: 100 μm in (A), 10 μm in (B-B, F, F′, C′, G′)