Fig. 7. Perturbed expression of cyclic genes during somitogenesis in Sfrp1^-/-;Sfrp2^-/- embryos. (A-G) Altered Lfng oscillating cycles in the PSM of Sfrp1^-/-;Sfrp2^-/- embryos at E8.5. The Lfng cycle was examined in control (A,D) and Sfrp1^-/-;Sfrp2^-/- (B,C,E,F) embryos by culture of half of the posterior region for different lengths of time [A, B and C, 0 and 60 minutes (t=0', 60'); D, E and F, 0 and 75 minutes (t=0', 75')]. The dagger indicates a strong extra stripe in the anterior-most region of the PSM. Scale bar: 250 µm. (G) Schematic diagram of Lfng expression in control and Sfrp1^-/-;Sfrp2^-/- explants. Traveling stripes of Lfng expression are indicated by numbers. (H,I) Oscillation pattern of Lfng in control (H) and Sfrp1^-/-;Sfrp2^-/- (I) explants at E9.5. Half of the posterior region was cultured for either 0 (t=0') or 75 (t=75') minutes. Scale bar: 250 µm. (J-U) Expression of Hes7, Axin2 and Nkx1 in the PSM of Sfrp1^-/-;Sfrp2^-/- embryos. Half of the posterior region was cultured for either 0 (t=0') or 75 (t=75') minutes. (J-O) Hes7 expression in control (J,M) and Sfrp1^-/-;Sfrp2^-/- (K,L,N,O) explants at E8.5. (L,N,O) Hes7 expression was perturbed in a large proportion of Sfrp1^-/-;Sfrp2^-/- explants. (K) Nearly normal Hes7 expression cycles were observed in Sfrp1^-/-;Sfrp2^-/- explants at lower frequency. The dagger indicates a strong extra stripe in the anterior-most region of the PSM. Scale bar: 250 µm. (P-R) Dynamic expression of Axin2 in control (P) and Sfrp1^-/-;Sfrp2^-/- (Q,R) explants at E8.5. An arrowhead indicates the higher expression domain of Axin2 in the primitive streak. Stripes of Axin2 expression were difficult to identify even in control explants at earlier embryonic stages. Scale bar: 250 µm. (S-U) Expression of Nkd1 in control (S) and Sfrp1^-/-;Sfrp2^-/- (T,U) explants at E8.5. Scale bar: 250 µm.