TIMP3 promotes the maintenance of neural stem-progenitor cells in the mouse subventricular zone.

Adult neural stem cells (NSCs) in the mouse subventricular zone (SVZ) serve as a lifelong reservoir for newborn olfactory bulb neurons. Recent studies have identified a slowly dividing subpopulation of embryonic neural stem-progenitor cells (NPCs) as the embryonic origin of adult NSCs. Yet, little is known about how these slowly dividing embryonic NPCs are maintained until adulthood while other NPCs are extinguished by the completion of brain development. The extracellular matrix (ECM) is an essential component of stem cell niches and thus a key determinant of stem cell fate. Here we investigated tissue inhibitors of metalloproteinases (TIMPs)-regulators of ECM remodeling-for their potential roles in the establishment of adult NSCs. We found that Timp2, Timp3, and Timp4 were expressed at high levels in slowly dividing NPCs compared to rapidly dividing NPCs. Deletion of TIMP3 reduced the number of adult NSCs and neuroblasts in the lateral SVZ. In addition, overexpression of TIMP3 in the embryonic NPCs suppressed neuronal differentiation and upregulated the expression levels of Notch signaling relating genes. These results thus suggest that TIMP3 keeps the undifferentiated state of embryonic NPCs, leading to the establishment and maintenance of adult NSCs.

Cell cycle arrest determines adult neural stem cell ontogeny by an embryonic Notch-nonoscillatory Hey1 module.

Quiescent neural stem cells (NSCs) in the adult mouse brain are the source of neurogenesis that regulates innate and adaptive behaviors. Adult NSCs in the subventricular zone are derived from a subpopulation of embryonic neural stem-progenitor cells (NPCs) that is characterized by a slower cell cycle relative to the more abundant rapid cycling NPCs that build the brain. Yet, how slow cell cycle can cause the establishment of adult NSCs remains largely unknown. Here, we demonstrate that Notch and an effector Hey1 form a module that is upregulated by cell cycle arrest in slowly dividing NPCs. In contrast to the oscillatory expression of the Notch effectors Hes1 and Hes5 in fast cycling progenitors, Hey1 displays a non-oscillatory stationary expression pattern and contributes to the long-term maintenance of NSCs. These findings reveal a novel division of labor in Notch effectors where cell cycle rate biases effector selection and cell fate.

Maintenance of neural stem-progenitor cells by the lysosomal biosynthesis regulators TFEB and TFE3 in the embryonic mouse telencephalon.

Lysosomes have recently been implicated in regulation of quiescence in adult neural stem cells (NSCs). Whether lysosomes regulate the differentiation of neural stem-progenitor cells (NPCs) in the embryonic brain has remained unknown, however. We here show that lysosomes are more abundant in rapidly dividing NPCs than in differentiating neurons in the embryonic mouse neocortex and ganglionic eminence. The genes for TFEB and TFE3, master regulators of lysosomal biosynthesis, as well as other lysosome-related genes were also expressed at higher levels in NPCs than in differentiating neurons. Anatomic analysis revealed accumulation of lysosomes at the apical and basal endfeet of NPCs. Knockdown of TFEB and TFE3, or that of the lysosomal transporter Slc15a4, resulted in premature differentiation of neocortical NPCs. Conversely, forced expression of an active form of TFEB (TFEB-AA) suppressed neuronal differentiation of NPCs in association with upregulation of NPC-related genes. These results together point to a previously unappreciated role for TFEB and TFE3, and possibly for lysosomes, in maintenance of the undifferentiated state of embryonic NPCs. We further found that lysosomes are even more abundant in an NPC subpopulation that rarely divides and includes the embryonic origin of adult NSCs than in the majority of NPCs that divide frequently for construction of the embryonic brain, and that overexpression of TFEB-AA also suppressed the cell cycle of neocortical NPCs. Our results thus also implicate lysosomes in establishment of the slowly dividing, embryonic origin of adult NSCs.

BMP signaling suppresses Gemc1 expression and ependymal differentiation of mouse telencephalic progenitors.

The lateral ventricles of the adult mammalian brain are lined by a single layer of multiciliated ependymal cells, which generate a flow of cerebrospinal fluid through directional beating of their cilia as well as regulate neurogenesis through interaction with adult neural stem cells. Ependymal cells are derived from a subset of embryonic neural stem-progenitor cells (NPCs, also known as radial glial cells) that becomes postmitotic during the late embryonic stage of development. Members of the Geminin family of transcriptional regulators including GemC1 and Mcidas play key roles in the differentiation of ependymal cells, but it remains largely unclear what extracellular signals regulate these factors and ependymal differentiation during embryonic and early-postnatal development. We now show that the levels of Smad1/5/8 phosphorylation and Id1/4 protein expression-both of which are downstream events of bone morphogenetic protein (BMP) signaling-decline in cells of the ventricular-subventricular zone in the mouse lateral ganglionic eminence in association with ependymal differentiation. Exposure of postnatal NPC cultures to BMP ligands or to a BMP receptor inhibitor suppressed and promoted the emergence of multiciliated ependymal cells, respectively. Moreover, treatment of embryonic NPC cultures with BMP ligands reduced the expression level of the ependymal marker Foxj1 and suppressed the emergence of ependymal-like cells. Finally, BMP ligands reduced the expression levels of Gemc1 and Mcidas in postnatal NPC cultures, whereas the BMP receptor inhibitor increased them. Our results thus implicate BMP signaling in suppression of ependymal differentiation from NPCs through regulation of Gemc1 and Mcidas expression during embryonic and early-postnatal stages of mouse telencephalic development.

Double-strand break repair based on short-homology regions is suppressed under terminal deoxynucleotidyltransferase expression, as revealed by a novel vector system for analysing DNA repair by nonhomologous end joining.

We have constructed a novel, nonhomologous end-joining (NHEJ) assay vector (NAV), containing mKate2, Venus and ccdB genes. Cotransfection of NAV with a construct expressing the restriction enzyme I-SceI generated a double-strand break (DSB) in NAV that excised mKate2 and ccdB. Repair of this DSB produced an intact vector that expressed Venus, a green fluorescent protein. Because cells bearing the repaired NAV lacked the ccdB gene which slows cell proliferation, the cultures were enriched in cells containing repaired DSBs. DNA sequence analysis of the DSB junctions indicated that the repair was carried out mainly by using the closest homology sequence. Use of the NAV yielded rapid results within 3 days after transfection. We then used the NAV to analyse NHEJ in cells overexpressing terminal deoxynucleotidyltransferase (TdT). The results indicated that TdT suppresses DNA repair that is based on short (one- or two-base) homology regions, to efficiently add deoxynucleotides during VDJ recombination in lymphoid cells.