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Fig. 6. Phosphomimetic Otx2-4E negatively regulates p27xic1. (A) Genome browser representation showing occupancies of Otx2 and Tle in Xenopus tropicalis gastrula embryos around the p27xic1 gene. (B-E) WISH analysis of p27xic1 at the neurula stage (stages 13-14). mRNA (30 pg/embryo) for globin (B), WT (C), 4E (D) or 4A (E) together with nbgal mRNA was injected in the presumptive posterior neuroectoderm at the four-cell stage. Dorsal view with anterior up. inj. indicates the injected side; uninj. indicates the uninjected side. Colors of numbers and arrowheads are the same as in Fig. 4. (C′,D′,E′) Enlarged image of C, D and E (dotted white box). (F-H) WISH and immunostaining of sagittal hemisection. WISH for otx2 and p27xic1 (F,G). Immunostaining of PH3 (H). Dorsal up, anterior to the left. (F′,G′,H′) Enlarged images of F,G, H (dashed gray box). Dashed blue or white lines indicate the position of the blastopore. (I) A schematic model of feedback loops involving Cdk, Otx2 and p27xic in cell-proliferation (left) and non-proliferation states (right). Left, upon growth stimulation, (1) activation of Cdk causes phosphorylation of Otx2; (2) phosphorylated Otx2 downregulates p27xic1; and (3) the reduction in p27xic1 increases Cdk activity, thereby enhancing both cell proliferation and a phosphorylation state of Otx2. Right, upon the reduction of growth stimulation, (1) reduced Cdk activity causes the reduction of phosphorylation of Otx2; (2) the reduction in phosphorylated Otx2 derepresses p27xic1; and (3) increased p27xic1 inhibits Cdk activity, thereby reducing both cell proliferation and a phosphorylation state of Otx2. Scale bars: 300 μm in BH,C′-H′. |
