β1-integrin deficient stem cells to form new neurospheres, but it influences the size of the neurosphere: β1-integrin deficient neurospheres were overall smaller due to increased cell death and reduced proliferation. while the neurosphere assay has been the method of choice for isolation, expansion and even the enumeration of neural stem and progenitor cells, several recent publications have highlighted some of the limitations of the neurosphere culture system as a method for determining neural stem cell frequencies. in collaboration with reynolds, stemcell technologies has developed a collagen-based assay, called the neural colony-forming cell (ncfc) assay, for the quantification of neural stem cells. importantly, this assay allows discrimination between neural stem and progenitor cells. history the first evidence that neurogenesis occurs in certain regions of the adult mammalian brain came from -thymidine labeling studies conducted by altman and das in 1965 which showed postnatal hippocampal neurogenesis in young rats. in 1989, sally temple described multipotent, self-renewing progenitor and stem cells in the subventricular zone (svz) of the mouse brain. in 1992, brent a. reynolds and samuel weiss were the first to isolate neural progenitor and stem cells from the adult striatal tissue, including the svz — one of the neurogenic areas — of adult mice brain tissue. in the same year the team of constance cepko and evan y. snyder were the first to isolate multipotent cells from the mouse cerebellum and stably transfected them with the oncogene v-myc. this molecule is one of the genes widely used now to reprogram adult non-stem cells into pluripotent stem cells. since then, neural progenitor and stem cells have been isolated from various areas of the adult central nervous system, including non-neurogenic areas, such as the spinal cord, and from various species including humans.