Neural Crest Does Not Contribute to the Neck and Shoulder in the Axolotl (Ambystoma mexicanum)
Figure 4
Results of additional experiments.
a, Sagittal section through the neck epaxial muscles in between the scapular tip and occipital region of the skull; this region is devoid of any neural crest-derived connective tissue. Only intersegmental nerves are present along the intermuscular septae are GFP+ (green arrowheads). b–e, transverse sections through the shoulder girdle region of a juvenile (1 month) containing two GFP+ neural folds (see Fig. 3a). The framed area in (b) is enlarged in (c–e). c–e, GFP+ spinal nerves close to the shoulder girdle cartilage (c) and Myelin Basic Protein+ cells (anti-MBP-Cy5 immunostaining) in (d) are co-localized (e) as indicated with white arrowheads. f–h, medial aspect of the right shoulder girdle (soft tissues included) of a mature axolotl (3 years) containing two short GFP+ neural fold fragments on either side (same experiment as in (Fig. 2a), but with short double- sided graft). f, bright field micrograph of an isolated shoulder girdle whole mount with framed areas enlarged in (g) and (h). The dorsal border of the ossified part of the scapulo-coracoid is indicated with black arrows. g, GFP+ spinal nerves over the GPP-negative ossified scapulo-coracoid. h, nerve net in the muscles connecting to the scapula. GFP+ cells are not present in muscle attachment sites (empty white arrowheads) and the tip of the scapula of somitic origin (white asterisks). Abbreviations: tr2, transverse process of the second vertebra; occ, occipital bone; other abbr. as in Figs. 1–3. Scale bars: a–e : 100 µm, f–h : 5 mm.