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Fig. 2. p27Xic1 is expressed in cells destined to a somitic fate. Embryos were analyzed by whole-mount in situ hybridization at the indicated stages for the expression of p27Xic1 (A-D,I,L) and MyoD (E-H,J). (A) p27Xic1 expression in the animal pole at stage 10. Lateral view with dorsal towards the left, asterisk marks the involuting dorsal lip. (B) p27Xic1 localizes to the presomitic mesoderm at stage 11 (arrow). Dorsal view, anterior is downwards. (C) Stage 15 embryo with p27Xic1 in the myotome, notochord, primary neurons and anterior placodes (arrows). Dorsal view with anterior downwards. (D) By stage 22, p27Xic1 is downregulated in the more mature, anterior somites. Lateral view, anterior left. (E) Lateral view of an embryo stained for MyoD at stage 10 with dorsal leftwards and animal pole upwards. V, ventral marginal zone; L, lateral marginal zone; asterisk, involuting dorsal lip. (F) MyoD is expressed in a horseshoe around the blastopore at stage 11. Dorsal view, asterisk indicates the notochord. (G) MyoD expression at stage 15. Dorsal view with anterior downwards. (H) MyoD expression at stage 22. (I) At stage 26, p27Xic1 is virtually absent from the anterior myotome. (J) MyoD is still highly expressed posteriorly at stage 26. (K) Double in situ hybridization demonstrating that p27Xic1 (light blue) is only expressed in the subset of MyoD (purple)-expressing cells that are destined to become skeletal muscle. Parallel horizontal lines indicate the extent of the region of overlap (purple/black). (L) Lateral view of a stage 13 embryo showing epidermal p27Xic1 expression. Dorsal left, anterior down. (M) p27Xic1 protein expression at stage 15. (N) Bisected embryo showing nuclear p27Xic1 expression at stage 15. (O) Hoechst staining of DNA in bisected embryo shown in N. |
