Fig. 1. Myosin IIB protein localization. (A-C) In tailbud-stage Xenopus embryos, MHC-B protein is localized to the dorsal axis (A), both at the surfaces of the somites (B) and in a polarized distribution in mature notochord (C). (D) Posterior notochordal cells actively undergoing convergent extension (CE) exhibit MHC-B localized to triple cell junctions inside the notochord (^*), where invasive protrusions extend between adjacent cells during intercalation, and at cell-cell-matrix junctions at the notochord-somite boundary (NSB) (arrowheads). (E) Basal (mesodermal side) view of MHC-B staining in a deep neural-over-mesoderm explant reveals that MHC-B exhibits a fibrillar distribution over notochord and somites. BA, brachial arches; N, notochord; S, somitic mesoderm. Scale bars: 500 µm, except 50 µm in D.