Figure 5.

Expression of key markers of somitogenesis including Fgf8 and Lunatic Fringe (Lfng) are dramatically decreased in the presomitic mesoderm of Mbtps1^cKO embryos. Whole mount in situ hybridization was performed at E9.5 (C and E), E10.5 (D, F and G–L) or E11.5 (A, B and M–R) in control and Mbtps1^cKO embryos. (A and B) Expression of Uncx4.1 reveals a general disorganization of the somites including loss of somite polarity in Mbtps1^cKO embryos, 3 days after the onset of the 3.6 Col1-Cre recombinase. (C–F) Expression of Fgf8, normally restricted to the posterior-most region of the PSM at E9.5 and E10.5 (brackets) (C and D), is absent in Mbtps1^cKO embryos at E10.5 (F), but still present a day earlier in Mbtps1^cKO embryos at E9.5 (E). (G–L) Lfng expression is greatly reduced and its cyclic expression disturbed in E10.5 Mbtps1^cKO embryos as demonstrated by dorsal (G–L) and lateral (G’–L’) views of the non-segmented PSM. (M–R) As illustrated by a representative sampling of three embryos, Mesp2 expression displays a range of expression in the determination front of Mbtps1^cKO embryos which is consistently less than that for controls. Scale bar: 100 µm.