Fig. 2. Math1 promoter activity is maintained in rhombic lip cultures, and is downregulated only in Math1-expressing cells. (A-L) CGC were cultured and grown for 3 days (A-F) or 6 days (G-L), and Math1 promoter activity detected by X-Gal staining. No background is seen in cells from Math1^+/+ (WT, A,D). Rhombic lip cells from both Math1^ß-gal/+ (Het, B,E) and Math1^{ß-gal/ß-gal} (Null, C,F) continue to express similar levels of lacZ after 3 days in vitro. By contrast, after 6 days, the rhombic lip cells from Math1^{ß-gal/ß-gal} display numerous positive cells (I,L), while in the Math1^ß-gal/+ a notable decrease in stained cells is observed (H,K). (M) Quantification of Math1 promoter activity presented as normalized activities +s.e.m. from cultures after 3 and 6 days in vitro. Math1^ß-gal/+ and Math1^{ß-gal/ß-gal} have very similar Math1 promoter activity after 3 days in culture, in contrast to a significant decrease in Math1^ß-gal/+ cells, and a significantly high level in Math1^{ß-gal/ß-gal} after 6 days in culture (P<0.001, t-test). Scale bar in A: 50 µm for A-C,G-I; 25 µm for D-F,J-L.