Fig. 7. Disturbances in expression of notch-delta pathway genes in rs mutants. Whole-mount in situ hybridization of rs/rs embryos (B,D,F,H,I,K,M,O) compared with stage-matched control embryos (A,C,E,G,J,L,N) at carefully selected stages of E9 (A-F) and of E10 (G-O) with probes for Dll1 (A-I), Mesp2 (J-M) and Lfng (N and O). Expression of Dll1 in rs/rs appears fairly normal up to E9.5 (B). However, stripe-like expression of Dll1 in the rostral PSM and in newly formed somites (black arrowheads in C-F) becomes unclear and less intense (red arrowheads in D,F) from E9.5 on (D), while strong Dll1 expression in the caudal two-thirds of the PSM is still maintained during late E9 (F), starts to reduce from early E10 (H), and diminishes by mid E10 (I). Surprisingly, Mesp2 expression in a stripe pattern in the rostral PSM continues, though significantly reduced in intensity, until late E10 in rs/rs (K,M). Dynamic and oscillating expression of Lfng in the PSM is also observed until early E10, but appears to cease by mid E10 in rs/rs (O). FL, forelimb buds; HL, hindlimb buds.