The molecular mechanisms of neurogenic fate determination are of particular importance in light of the need to regenerate neurons. Here we define the mechanisms of installing neurogenic fate by the transcription factor Pax6 acting together with the Brg1-containing BAF chromatin remodeling complex. We show that Pax6 physically interacts with Brg1-containing BAF complex and genetic deletion of either Pax6 or Brg1, in the neural stem cells in the adult mouse subependymal zone results in a strikingly similar fate conversion from neuronal progenitors to glia. The Pax6-BAF complex drives neurogenesis by directly activating transcription factors Sox11, Nfib and Pou3f4, which form a cross-regulatory network that maintains neurogenic fate downstream of the Pax6-BAF complex in neuroblasts. Our work identifies a novel concept of stratification in neural fate commitment with a strikingly specific role of the Pax6-BAF complex in initiating a cross-regulatory network essential for maintenance of the neurogenic lineage in the adult brain.

Although the local environment is known to regulate neural stem cell (NSC) maintenance in the central nervous system, little is known about the molecular identity of the signals involved. Chondroitin sulfate proteoglycans (CSPGs) are enriched in the growth environment of NSCs both during development and in the adult NSC niche. In order to gather insight into potential biological roles of CSPGs for NSCs, the enzyme chondroitinase ABC (ChABC) was used to selectively degrade the CSPG glycosaminoglycans. When NSCs from mouse E13 telencephalon were cultivated as neurospheres, treatment with ChABC resulted in diminished cell proliferation and impaired neuronal differentiation, with a converse increase in astrocytes. The intrauterine injection of ChABC into the telencephalic ventricle at midneurogenesis caused a reduction in cell proliferation in the ventricular zone and a diminution of self-renewing radial glia, as revealed by the neurosphere-formation assay, and a reduction in neurogenesis. These observations suggest that CSPGs regulate neural stem/progenitor cell proliferation and intervene in fate decisions between the neuronal and glial lineage.

Neural stem cells have been documented in both the developing and the mature adult CNSs of mammals. This cell population holds a considerable promise for therapeutical applications in a wide array of CNS diseases. Therefore, universally applicable strategies for the purification of this population to further its cell biological characterization are sought. Here, we report that the unique chondroitin sulfate epitope recognized by the monoclonal antibody 473HD is surface expressed on actively cycling, multipotent progenitor cells of the developing telencephalon with radial glia-like properties. When used for immunopanning, the antibody enriched at least threefold for neural stem/progenitor cells characterized by the ability to self-renew as neurospheres that generated all major neural lineages in differentiation assays. In contrast, the 473HD-depleted cell fraction was mostly devoid of neurosphere-forming cells. The isolation of 473HD-positive adult multipotent progenitors from the subependymal zone of the lateral ventricle wall revealed a substantial overlap with the known adult neural stem cell marker LewisX. When the chondroitin sulfates were removed from immunoselected 473HD-positive neural stem/progenitor cell surfaces by chondroitinase ABC treatment or perturbed by the monoclonal antibody 473HD that recognizes the unique DSD-1 chondroitin sulfate epitope, the generation of neurospheres was significantly reduced. Thus, the 473HD epitope could not only be used for the isolation of multipotent neural progenitors during forebrain development as well as from the adult neurogenic niche but may also constitute a functionally important entity of the neural stem cell niche.

Lissencephaly is a severe brain malformation in humans. To study the function of the gene mutated in lissencephaly (LIS1), we deleted the first coding exon from the mouse Lis1 gene. The deletion resulted in a shorter protein (sLIS1) that initiates from the second methionine, a unique situation because most LIS1 mutations result in a null allele. This mutation mimics a mutation described in one lissencephaly patient with a milder phenotype. Homozygotes are early lethal, although heterozygotes are viable and fertile. Most strikingly, the morphology of cortical neurons and radial glia is aberrant in the developing cortex, and the neurons migrate more slowly. This is the first demonstration, to our knowledge, of a cellular abnormality in the migrating neurons after Lis1 mutation. Moreover, cortical plate splitting and thalomocortical innervation are also abnormal. Biochemically, the mutant protein is not capable of dimerization, and enzymatic activity is elevated in the embryos, thus a demonstration of the in vivo role of LIS1 as a subunit of PAF-AH. This mutation allows us to determine a hierarchy of functions that are sensitive to LIS1 dosage, thus promoting our understanding of the role of LIS1 in the developing cortex.brain development ͉ lissencephaly ͉ platelet-activating factor ͉ acetylhydrolase ͉ gene targeting L IS1 was identified as the gene mutated in a severe human developmental brain malformation known as lissencephaly (''smooth brain'') type I (1). Patients with lissencephaly often are severely retarded, epileptic, and die at a young age. The most striking feature of the brains of affected individuals is that they are smooth and largely devoid of the sulci and gyri that characterize the normal brain. The lissencephalic brain exhibits defects in neuronal migration that result in poor organization of cortical layering. A reduced surface area and lack of cortical folds are also seen, possibly because of an overall reduced number of neurons (2). Mutations in two different genes may result in type I lissencephaly: LIS1, an autosomal gene located on chromosome 17p13.3 (1), and doublecortin, an X-linked gene (3, 4). The pattern of expression of LIS1 in the nervous system suggested that the mouse would be a suitable organism for studying the role of LIS1 during brain development (5). Mouse embryos homozygous for the null Lis1 allele (Lis1Ϫ͞Ϫ) die after implantation, whereas heterozygotes are viable and fertile (6). A half dosage of LIS1 affects neuronal migration only slightly in the developing cortex, whereas adult layer organization appears normal. Further gene dosage reduction severely obstructs cortical and hippocampal organization (6). LIS1 interacts with many proteins and is involved in several basic cellular functions, including mitosis, nuclear positioning, and microtubule regulation (for review, see ref. 7). To better understand the function of LIS1 and its role in neuronal migration, we produced Lis1 mutant mice by using cre recombinase-mediated loxP deletion. Our mutation resulted in a shorter LIS1 p...