Figure 3. Expression of snail in vivo (A) and in vitro (B–G) detected by whole-mount in situ hybridization (positive signal is dark or reddish-blue). Palatal shelves (n = 3–7/group) were either cultured in proximity to allow fusion to occur (B-D) or placed apart (E-G). (A) Transverse section of the whole-mount in situ hybridization of an E14.5 (n = 5), showing strong snail expression in the mesenchyme of the fusing palatal shelves, but not in the epithelium of the MES. (B-C) A similar pattern of snail expression is observed in fusing palatal shelves cultured for 30 and 48 hrs, with a weaker signal restricted to the lateral aspect (asterisks) observed at 48 hrs when the MES is being disrupted. (D) snail expression decreases as fusion progresses and is hardly detectable after 60 hrs in culture. (E,F,G) snail expression in palates that are not allowed to fuse decreases over time, as in fusing palatal shelves (B-D). Scale bars: A = 300 µm, B-G = 500 µm. N = nasal aspect, O = oral aspect, t = tooth bud. Color version of this figure is available online as an Appendix.