Fig. 4. Segmentation and cell differentiation in somites of Sfrp1^-/-;Sfrp2^-/- embryos. (A-N) Somite segmentation was aberrant in the region between the forelimb and hindlimb in Sfrp1^-/-;Sfrp2^-/- embryos. However, cell differentiation in the somite did occur in that region. (A-D) Expression of Mox1 in control (A,B) and Sfrp1^-/-;Sfrp2^-/- (C) embryos at E9.5. D shows a higher magnification of the region indicated in C. Arrowheads indicate irregular segmentation of the somite. Pax3 (E-H), Uncx4.1 (I-K) and myogenein (L-N) expression in control (E,F,I,J,L,M) and Sfrp1^-/-;Sfrp2^-/- (G,K,N) embryos at E9.5. H shows the region indicated in G at higher magnification. Arrowheads indicate irregular segmentation of the somite. Asterisks indicate somite positions in the Sfrp1^-/-;Sfrp2^-/- embryo (N) corresponding to those of the control embryo (M). (O-Q) Dll1 expression in control (O,P) and Sfrp1^-/-;Sfrp2^-/- (Q) embryos. Note that the PSM region was severely affected in the double homozygous mutant embryos. (R-T) Myogenein expression in control (R) and Sfrp1^-/-;Sfrp2^-/- (S) embryos. The number of somites decreased in the region between the forelimb and hindlimb in the Sfrp1^-/-;Sfrp2^-/- embryo. T displays higher magnification of the region indicated in S. FL, forelimb; HL, hindlimb. Scale bar: 500 µm.