Figure 4.

Disrupted somite polarity in transgenic embryos. Uncx4.1 (A,C,E,G,I,K) and Tbx18 (B,D,F,H,J,L) expression in wild-type (A,B), T(s)∷Cre; R-NICD (C,D), Dll1^−/− (E,F), Pofut1^−/− (G,H), T(s)∷Cre; R-NICD; Dll^lox/lox (I,J), and T(s)∷Cre; N1^loxp/loxP (K,L) embryos, indicating that constitutive Notch activity leads to caudalization of somites (C,D,I,J) and loss of all Notch activity to rostralization (E–H), whereas loss of Notch1 function alone has no significant impact on segment polarity (K,L).