Area-Specific Regulation of Quiescent Neural Stem Cells by Notch3 in the Adult Mouse Subependymal Zone.

In the adult mammalian brain, neural stem cells (NSCs) generate new neurons throughout the mammal's lifetime. The balance between quiescence and active cell division among NSCs is crucial in producing appropriate numbers of neurons while maintaining the stem cell pool for a long period. The Notch signaling pathway plays a central role in both maintaining quiescent NSCs (qNSCs) and promoting cell division of active NSCs (aNSCs), although no one knows how this pathway regulates these apparently opposite functions. Notch1 has been shown to promote proliferation of aNSCs without affecting qNSCs in the adult mouse subependymal zone (SEZ). In this study, we found that Notch3 is expressed to a higher extent in qNSCs than in aNSCs while Notch1 is preferentially expressed in aNSCs and transit-amplifying progenitors in the adult mouse SEZ. Furthermore, Notch3 is selectively expressed in the lateral and ventral walls of the SEZ. Knockdown of Notch3 in the lateral wall of the adult SEZ increased the division of NSCs. Moreover, deletion of the Notch3 gene resulted in significant reduction of qNSCs specifically in the lateral and ventral walls, compared with the medial and dorsal walls, of the lateral ventricles. Notch3 deletion also reduced the number of qNSCs activated after antimitotic cytosine ß-D-arabinofuranoside (Ara-C) treatment. Importantly, Notch3 deletion preferentially reduced specific subtypes of newborn neurons in the olfactory bulb derived from the lateral walls of the SEZ. These results indicate that Notch isoforms differentially control the quiescent and proliferative steps of adult SEZ NSCs in a domain-specific manner.SIGNIFICANCE STATEMENT In the adult mammalian brain, the subependymal zone (SEZ) of the lateral ventricles is the largest neurogenic niche, where neural stem cells (NSCs) generate neurons. In this study, we found that Notch3 plays an important role in the maintenance of quiescent NSCs (qNSCs), while Notch1 has been reported to act as a regulator of actively cycling NSCs. Furthermore, we found that Notch3 is specifically expressed in qNSCs located in the lateral and ventral walls of the lateral ventricles and regulates neuronal production of NSCs in a region-specific manner. Our results indicate that Notch3, by maintaining the quiescence of a subpopulation of NSCs, confers a region-specific heterogeneity among NSCs in the adult SEZ.

Notch3 null mutation in mice causes muscle hyperplasia by repetitive muscle regeneration.

Satellite cells are skeletal muscle stem cells responsible for growth, maintenance, and repair of postnatal skeletal muscle. Although several studies have demonstrated that Notch signaling plays a critical role in muscle regeneration through promoting proliferation and self-renewal of satellite cells, the function of Notch3 is yet to be elucidated. We analyzed muscle regeneration in Notch3-deficient mutant mice. We found a remarkable overgrowth of muscle mass in the Notch3-deficient mice but only when they suffered repetitive muscle injuries. Immunochemical analysis found that Notch3 was expressed in Pax7(+)/MyoD(-) quiescent satellite cells and also in Pax7(+)/MyoD(+)-activated satellite cells, but the expression was restricted to around half the population of each cell type. In Notch3-deficient mice, the number of sublaminar quiescent satellite cells was significantly increased compared with those in control mice. We also found that primary cultured myoblasts isolated from the Notch3-deficient mice proliferated faster than those from control mice. Analysis of cultured myofibers revealed that the number of self-renewing Pax7-positive satellite cells attached to the myofiber was increased in the Notch3-deficient mice when compared with control mice. The data obtained in this study suggested that Notch3 pathway might be distinct from Notch1 in muscle regeneration. Because overexpression of Notch3 activated the expression of Nrarp, a negative feedback regulator of Notch signaling, Notch3 might act as a Notch1 repressor by activating Nrarp.

Functional redundancy of the Notch gene family during mouse embryogenesis: analysis of Notch gene expression in Notch3-deficient mice.

The Notch3 gene, a member of the Notch gene family, is expressed in a wide variety of tissues during development. We generated and analyzed Notch3-deficient mice to assess the in vivo role of the Notch3 gene. Consistent with previous observation of Krebs et al. [Characterization of Notch3-deficient mice: normal embryonic development and absence of genetic interactions with a Notch1 mutation, Genesis 37 (3) (2003) 139-143], the Notch3-/- mice were viable, fertile, and developed normally despite abundant expression of Notch3 in various embryonic tissues. We examined the details of Notch1, 2, and 4 expressions in the Notch3-/- embryos compared with those in wild-type embryos. As a result, we found that a deficiency in Notch3 did not affect the expression of Notch1, 2, and 4, and that either Notch1 or Notch2, or sometimes both, was always expressed in all Notch3-expressing tissues examined. These results support the idea that other Notch genes functionally compensate for Notch3 during embryonic development. We also surveyed the adult tissues of Notch3-/- mice and found significantly fewer thymocytes in 10-week-old mice. Therefore, the thymus might be a target tissue affected by Notch3 deficiency.

Early embryonic lethality caused by targeted disruption of the mouse PHGPx gene.

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is the only known intracellular antioxidant enzyme that can directly reduce lipid hydroperoxide in membrane. Mitochondrial and non-mitochondrial PHGPx and sperm nuclei GPx are transcribed from one gene by alternative transcription using different first exons Ia and Ib, respectively. To examine the role of PHGPx in development, we generated mice deficient in PHGPx by a targeted disruption of all exons of the PHGPx gene. Heterozygotes are viable, fertile, and appear normal, despite having decreased levels of three types of PHGPx mRNA and protein. Embryos homozygous for PHGPx-null die between 7.5 and 8.5 days post coitum (dpc), probably developing distal apoptosis. We examined the expression of PHGPx in mouse embryos using immunohistochemical analysis with anti-PHGPx mAb. The expression of PHGPx was detected in the embryonic ectoderm and the yolk sac membrane at 7.5dpc. The results demonstrated that PHGPx is expressed in early gastrulation stage at 7.5dpc and that the expression of PHGPx was essential for normal mouse development.