Pygopus - a core component of the canonical Wnt-signalling pathway - plays a crucial role in development and disease. Its essential transcriptional co-activator activity is mediated through its interaction with β-catenin,Tcf, Bcl9 and Hyrax. In Xenopus, Pygopus 2 (Pygo2) orthologues regulate the expression of eye markers. Surprisingly though, it has been suggested that this activity operates independently of the Wnt pathway. Richard Lang and co-workers(p. 1873) now show that lens development in mice depends on Pygo2-mediated regulation of the transcription factor Pax6. They further show that Pygo2 function, in this setting, is Wnt-independent. By conditionally deleting Pygo2 in certain tissues in mice where it is normally expressed - the ocular mesenchyme and the presumptive lens ectoderm (PLE) - these researchers show that Pax6 expression is reduced in the PLE and a small lens subsequently develops. Interestingly, they find that Pygo1 is dispensable for lens development. Future work...

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