Pbx1 is required for adult subventricular zone neurogenesis.

TALE-homeodomain proteins function as components of heteromeric complexes that contain one member each of the PBC and MEIS/PREP subclasses. We recently showed that MEIS2 cooperates with the neurogenic transcription factor PAX6 in the control of adult subventricular zone (SVZ) neurogenesis in rodents. Expression of the PBC protein PBX1 in the SVZ has been reported, but its functional role(s) has not been investigated. Using a genetic loss-of-function mouse model, we now show that Pbx1 is an early regulator of SVZ neurogenesis. Targeted deletion of Pbx1 by retroviral transduction of Cre recombinase into Pbx2-deficient SVZ stem and progenitor cells carrying floxed alleles of Pbx1 significantly reduced the production of neurons and increased the generation of oligodendrocytes. Loss of Pbx1 expression in neuronally committed neuroblasts in the rostral migratory stream in a Pbx2 null background, by contrast, severely compromised cell survival. By chromatin immunoprecipitation from endogenous tissues or isolated cells, we further detected PBX1 binding to known regulatory regions of the neuron-specific genes Dcx and Th days or even weeks before the respective genes are expressed during the normal program of SVZ neurogenesis, suggesting that PBX1 might act as a priming factor to mark these genes for subsequent activation. Collectively, our results establish that PBX1 regulates adult neural cell fate determination in a manner beyond that of its heterodimerization partner MEIS2.

A fast and simple differentiation protocol to study the pro-neurogenic activity of soluble factors in neurospheres.

Sphere-forming assays are widely used for the propagation, characterization and manipulation of adult brain-derived stem- and progenitor cells. However despite the broad application of this cell culture system in neural stem cell- and brain tumor research, no standardized protocols exist. Variations in experimental procedures not only concern the use of media components but also cell density, the number of passages the cells are propagated before analysis and, in cases where the neurogenic or gliogenic potential of the cells is investigated, the duration that the cells are allowed to differentiate. The latter deserves consideration because the proportion of differentiated cells obtained at the endpoint of the experiment depends not only on the absolute number of cells that differentiate at a given time, but also on the number of cell divisions prior to differentiation and the rate of cell death in the cultures. In the present study we describe a fast and simple differentiation protocol to investigate the pro-neurogenic potential of soluble factors added to subventricular zone (SVZ)-derived neurospheres. The assay relies on the use of primary neurospheres and very short differentiation times, thereby largely excluding the contribution of cell proliferation and cell death to the results. We use this modified assay to test the consequence of pharmacological inhibition of the EGF receptor-, Erk1/2-, Protein Kinase B/AKT-, and Sonic Hedgehog-pathways on neuronal differentiation of SVZ-neurosphere cultures.

Meis2 is a Pax6 co-factor in neurogenesis and dopaminergic periglomerular fate specification in the adult olfactory bulb.

Meis homeodomain transcription factors control cell proliferation, cell fate specification and differentiation in development and disease. Previous studies have largely focused on Meis contribution to the development of non-neuronal tissues. By contrast, Meis function in the brain is not well understood. Here, we provide evidence for a dual role of the Meis family protein Meis2 in adult olfactory bulb (OB) neurogenesis. Meis2 is strongly expressed in neuroblasts of the subventricular zone (SVZ) and rostral migratory stream (RMS) and in some of the OB interneurons that are continuously replaced during adult life. Targeted manipulations with retroviral vectors expressing function-blocking forms or with small interfering RNAs demonstrated that Meis activity is cell-autonomously required for the acquisition of a general neuronal fate by SVZ-derived progenitors in vivo and in vitro. Additionally, Meis2 activity in the RMS is important for the generation of dopaminergic periglomerular neurons in the OB. Chromatin immunoprecipitation identified doublecortin and tyrosine hydroxylase as direct Meis targets in newly generated neurons and the OB, respectively. Furthermore, biochemical analyses revealed a previously unrecognized complex of Meis2 with Pax6 and Dlx2, two transcription factors involved in OB neurogenesis. The full pro-neurogenic activity of Pax6 in SVZ derived neural stem and progenitor cells requires the presence of Meis. Collectively, these results show that Meis2 cooperates with Pax6 in generic neurogenesis and dopaminergic fate specification in the adult SVZ-OB system.