Wnt reporters in animals
There are various "reporter transgenes" that respond to Wnt signals in intact animals and therefore, as far as one can know, reflect endogenous Wnt signaling (reviewed in Barolo, 2006). These reporters are based on a multimerized TCF binding site, driving expression of LacZ or GFP. Other lines allow for lineage tracing of Wnt responding cells, using the Cre/ERT2 gene inserted into Wnt target genes.
Animal strain (linked to resource) | reporter | reference |
| TOP-GAL (obtain from Jackson Labs) | 3 TCF sites, c-fos promoter, LacZ | Gupta and Fuchs (1999) |
| BAT-GAL | TCF sites, Siamois promoter | Maretto et al (2003), |
| ins-TOPEGFP, ins-TOPGAL | TCF sites, LacZ or GFP, insulator elements | Moriyama (2007) |
| LEF-EGFP | TCF sites, EGFP | Currier et al, (2010). |
| Axin2-LacZ (obtain from Jackson Labs) | Insert of LacZ into Axin2, Wnt target gene | Lustig et al, (2002) |
| Axin2-d2EGFP | Axin2 promoter, EGFP | Jho et al, (2002), |
| Lgr5tm1(cre/ERT2) (obtain from Jackson Labs) | Cre/ERT2 insert into LGR5, Wnt target gene | Barker et al (2007) |
| Axin2-Cre/ERT2 (order from Jackson Labs) | Cre/ERT2 insert into Axin2, Wnt target gene | Van Amerongen (2012) |
| TOPdGFP Zebrafish | TCF sites, dGFP | Dorsky and Moon (2002) |
| Tcf/Lef-miniP:dGFP Zebrafish | TCF sites, dGFP | Shimizu et al, 2012 |
Movie: Expression of Tcf/Lef-miniP:dGFP in the Zebrafish embryo. From Shimizu et al, 2012
In response to the often-asked question "what is the best Wnt reporter", there is no simple answer. In our experience, Axin2/Conductin is widely expressed in areas where one would expect it, and might be an optimal reporter for many tissues. However, there are cells (in the lung for example) that are positive for the TOP-GAL reporter and negative for Axin2-based reporters (unpublished observations). The problem of reliably detecting Wnt signaling in vivo is compounded by difficulties in assessing Wnt gene expression itself (which is best done by in situ hybridization as antibodies are rarely good enough), or in finding other independent hallmarks of Wnt signaling (see Barolo, 2006 for a discussion).
