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Fig. 7. XMyoD and XMyf5 expression distinguish several myogenic cell populations in Xenopus somites. XMyf5 (A,C,D,G-I) and XMyoD (B,E,F,J) mRNA was detected in whole-mount in situ hybridisation of stage 35 embryos. Sections of stained embryos at the approximate positions shown in A and B were mounted without further treatment (H,J) or after immunohistochemical staining for MyHC (C-G) or PCNA (I). (A,B) Whole-mount embryos showing the distinct expression of XMyf5 and XMyoD, with section positions marked. (C-F) Trunk level sections showing that the superficial (dermomyotome, brackets) layer of the somite has distinct morphology, lacks MyHC expression and expresses XMyf5 in dorsomedial (shown magnified in D) and ventrolateral lips, and in rare cells away from the lips (C, arrows). XMyoD, by contrast, is expressed within the superficial myotome (E,F, arrowheads) and in the most dorsal dermomyotomal cells (E, arrow). (G-I) Tail sections showing that XMyf5 transcript is located medially in undifferentiated posterior tailbud (G). The outer layer of mesoderm lacks XMyf5 (brackets). Cells with less signal appear orientated perpendicular to the notochord in slightly more anterior regions and are most obvious at dorsal and ventral somite extremes (H). The nuclei of some of these XMyf5-expressing cells contain PCNA (I). (J) XMyoD expression is primarily superficial within the somite in tail tip (bracket). (K-M) Col1a1 is expressed in trunk regions at stage 25 (K) and more widely at stage 37 (L), and vibratome sections reveal expression in epidermis and more weakly in underlying dermomyotome (M, arrowheads). |
