The adult rodent subventricular zone (SVZ) is a neurogenic niche that provides new neurons and glia to the brain. A number of transcription factors, including MEIS2 and PAX6, are known to be required to promote the neuronal cell fate. PBX family proteins can interact with both MEIS and PAX family factors, and PBX1 is known to be expressed in the adult mouse forebrain. Dorothea Schulte and colleagues therefore set out to test the role of PBX1 in SVZ neurogenesis (p. ). They show that Pbx1 expression is found in rapidly proliferating SVZ progenitors, as well as in subsets of their progeny in the olfactory bulb. Its ortholog, PBX2, is more widely expressed in the forebrain. Deletion of both genes in the adult SVZ leads to a reduction in neurogenesis and a concomitant increase in oligodendrogliogenesis – an alternative fate for SVZ progenitors. Although the authors can detect PBX1 binding to MEIS2 and PAX6, the phenotype is distinct from functional blockade of these factors, suggesting an at least partially independent function. Intriguingly, PBX1 appears to bind its targets before they are transcriptionally activated, indicating a putative pioneer factor function for PBX1. These data identify PBX1 as an important new regulator of SVZ neurogenesis.
