Stem cells are found in various organs where they participate in tissue homeostasis by replacing differentiated cells lost to physiological turnover or injury. An investigation was performed to determine whether stem cells are restricted to produce specific cell types, namely, those from the tissue in which they reside. After transplantation into irradiated hosts, genetically labeled neural stem cells were found to produce a variety of blood cell types including myeloid and lymphoid cells as well as early hematopoietic cells. Thus, neural stem cells appear to have a wider differentiation potential than previously thought.

For most of the past century, the prospect of replacing lost or damaged cells in the central nervous system (CNS) was hampered by the opinion that the adult mammalian CNS was incapable of generating new nerve cells. This belief, like most dogmas, was essentially founded on a lack of experimental evidence to the contrary. The overturning of this 'no new neuron' hypothesis began midway through the twentieth century with a series of reports documenting neurogenesis in the postnatal and adult brain, continued with the isolation and in vitro culture of neurogenic cells from the adult mammalian brain, and culminated in the discovery of a population of multipotent, self-renewing cells in the adult CNS (that is, bona fide neural stem cells). Although a variety of techniques were initially used, the neurosphere assay (NSA) rapidly emerged as the assay of choice and has since become a valuable tool for isolating, and understanding the biology of, embryonic and adult CNS stem cells. Like all technologies, it is not without its limitations. In this article we will highlight several shortcomings of the assay related to its application and interpretation that we believe have led to a significant body of research whose conclusions may well be misleading.

The adult mammalian central nervous system (CNS) contains a population of neural stem cells (NSCs) with properties said to include the generation of non-neural progeny. However, the precise identity, location and potential of the NSC in situ remain unclear. We purified NSCs from the adult mouse brain by flow cytometry, and directly examined the cells' properties. Here we show that one type of NSC, which expresses the protein nestin but only low levels of PNA-binding and HSA proteins, is found in both ependymal and subventricular zones and accounts for about 63% of the total NSC activity. Furthermore, the selective depletion of the population of this stem cell in querkopf mutant mice (which are deficient in production of olfactory neurons) suggests that it acts as a major functional stem cell in vivo. Most freshly isolated NSCs, when co-cultured with a muscle cell line, rapidly differentiated in vitro into myocytes that contain myosin heavy chain (MyHC). This demonstrates that a predominant, functional type of stem cell exists in the periventricular region of the adult brain with the intrinsic ability to generate neural and non-neural cells.

Advancement in our understanding of the biology of adult stem cells and their therapeutic potential relies heavily on meaningful functional assays that can identify and measure stem cell activity in vivo and in vitro. In the mammalian nervous system, neural stem cells (NSCs) are often studied using a culture system referred to as the neurosphere assay. We previously challenged a central tenet of this assay, that all neurospheres are derived from a NSC, and provided evidence that it overestimates NSC frequency, rendering it inappropriate for quantitation of NSC frequency in relation to NSC regulation. Here we report the development and validation of the neural colony-forming cell assay (NCFCA), which discriminates stem from progenitor cells on the basis of their proliferative potential. We anticipate that the NCFCA will provide additional clarity in discerning the regulation of NSCs, thereby facilitating further advances in the promising application of NSCs for therapeutic use. STEM CELLS 2008;26:988 -996 Disclosure of potential conflicts of interest is found at the end of this article.

No abstract

No abstract

The adult mammalian brain maintains populations of neural stem cells within discrete proliferative zones. Understanding of the molecular mechanisms regulating adult neural stem cell function is limited. Here, we show that MYST family histone acetyltransferase Querkopf (Qkf, Myst4, Morf)-deficient mice have cumulative defects in adult neurogenesis in vivo, resulting in declining numbers of olfactory bulb interneurons, a population of neurons produced in large numbers during adulthood. Qkf-deficient mice have fewer neural stem cells and fewer migrating neuroblasts in the rostral migratory stream. Qkf gene expression is strong in the neurogenic subventricular zone. A population enriched in multipotent cells can be isolated from this region on the basis of Qkf gene expression. Neural stem cells/progenitor cells isolated from Qkf mutant mice exhibited a reduced self-renewal capacity and a reduced ability to produce differentiated neurons. Together, our data show that Qkf is essential for normal adult neurogenesis.

The exercise-induced enhancement of learning and memory, and its ability to slow age-related cognitive decline in humans led us to investigate whether running stimulates periventricular (PVR) neural stem cells (NSCs) in aging mice, thereby augmenting the regenerative capacity of the brain. To establish a benchmark of normal aging on endogenous NSCs, we harvested the PVR from serial vibratome sections through the lateral ventricles of juvenile (6-8 weeks), 6-, 12-, 18-, and 24-month-old mice, culturing the cells in the neural colony-forming cell assay. A significant decline in NSC frequency was apparent by 6 months ($40%), ultimately resulting in a $90% reduction by 24 months. Concurrent with this decline was a progressive loss in regenerative capacity, as reflected by an incomplete repopulation of neurosphere-forming cells following gamma cell irradiation-induced depletion of the PVR. However, voluntary exercise (i.e., 21 days of running) significantly increased NSC frequency in mice ! 18 months of age, augmenting the regeneration of irradiation-ablated periventricular cells and restoring NSC numbers to youthful levels. Importantly, and consistent with the demonstrated ability of growth hormone (GH) to increase NSC proliferation, and the elevated secretion of GH during exercise, exercise failed to stimulate NSCs in GH receptor-null mice. These findings now provide a novel basis for understanding the ability of exercise to delay the onset and rate of decline in neurodegenerative conditions not typically associated with the hippocampus and suggest that the GH-dependent activation of endogenous NSCs may be effective in reversing or preventing age-related neurodegeneration in humans. STEM CELLS