Figure 4. Canonical Wnt activity is present in the ventral telencephalon.
(a) Tcf4, a transcription factor and effector of canonical Wnt signaling, is expressed in the ventricular zone of the medial ganglionic eminence (MGE) in this section from an E12.5 embryo. (b–h) Analysis of canonical Wnt activity in the developing telencephalon using a transgenic Wnt reporter line (TCF-LacZ)38. The samples shown in (b–d) or in (e–h) were maintained in the same staining solution for equivalent lengths of time. (b) Apart from a small level of background activity in the choroid plexus, no lacZ activity is evident in the telencephalon of mice not containing the TCF-LacZ transgene. (c, d) Two examples of reporter activity from different TCF-LacZ embryos. The stronger reporter signal in d may indicate that it is homozygous for the TCF-LacZ transgene. In addition to the strong signal present in the medial cortex, the ventral telencephalon, including the lateral and medial ganglionic eminences and the preoptic area also show TCF-LacZ activity. (e–h) Coronal slices of E12.5 TCF-LacZ– (e) and TCF-LacZ+ (f–h) embryos were cultured for 1 day in vitro (div) in the absence (e, f) or presence (g, h) of the Wnt inhibitor Dkk1 before staining with X-gal to reveal reporter activity. (e) No signal is detected in the slice not containing the TCF-LacZ transgene. (f) Reporter activity is robust in a TCF-LacZ+ slice, and this activity is reduced within the mid to lateral cortex, as well as in the MGE (arrows), by Dkk1 (g, h). Cx-cortex, LGE-lateral ganglionic eminence, MGE-medial ganglionic eminence, PoA-preoptic area. Scale bar: 200 µm.