Outside of the central nervous system, there was remarkable β-gal staining in the spinal ganglia (Fig. 3), the intestine (Fig. 4A) and the tongue (Fig. 4C) of ED18.5 transgenic animals. There were lower levels of β-gal staining in the retina, trigeminal ganglia and lips (Table 2). Again, for the most part, these results are consistent with β4 mRNA localization studies (Winzer-Serhan and Leslie, 1997; Zoli et al., 1995). Two notable exceptions are the intestine and the lips, for which we are not aware of any reports describing the presence of β4 mRNA in ED18.5 animals. The presence of β-gal staining in these areas may be due to positional effects on transgene expression or it could be due to the lack of a cell-type-specific repressor element we previously identified in an intron of the nACh receptor α3 subunit gene, which we showed represses β4 promoter activity in cells that do not express the β4 subunit gene (Fuentes Medel and Gardner, 2007).
