Fig. 3. Mesp2 induces the degradation of Tbx6 via a ubiquitin-proteasome pathway. (A-D) Comparison of the expression patterns for Tbx6 protein (A,B) and mRNA (C,D) between wild-type (+/+) and Mesp2-null (P2L/P2L) mice. Dorsal views, anterior to the left. n=4 (A), n=3 (B), n=3 (C), n=4 (D). (E) The stability of Tbx6 was compared in embryonic tails with or without Mesp2. The time was estimated by the number of somites formed in the wild-type embryo. (F,G) Caudal portions of E10 embryos were bisected and the left halves treated with DMSO (control), while the right halves were treated with MG132 (F, n=10) or PMSF (G, n=3) and immunostained for Tbx6. (H-M) Double-immunostaining patterns representative of the relationships between Mesp2, Tbx6 and Notch during somitogenesis. The stained sections shown in the vertical rows are derived from a single embryo. A schematic of the Notch activity pattern used to assign the phase of the embryo is shown in the top panels; phase III (n=6), phase II (n=9), phase I (n=5). The proteins being detected are indicated in the left panels. A-P, anterior-posterior; D-V, dorsal-ventral.