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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).
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