Where new neurons come from

Where new neurons come from he brain has come alive with the sightings of stem cells, but the molecular handles on those cells are few. On page 169, Belachew et al. identify and characterize a new population of neural stem cells (NSCs) that can generate neurons in the postnatal mouse brain. In previous work, the researchers identified cells that express CNP in transgenic mice using a CNP-GFP marker. CNP is made in immature oligodendrocytes, so it is not surprising that the GFP-positive cells also express the proteoglycan NG2, which is also found in oligodendrocytes. But NG2 ϩ cells are also present in parts of the CNS that contain NSCs, and are the major cell type that continues to divide in the adult CNS. The significance of these facts has remained unclear, as the function of NG2 in cell types other than oligo-T Lamas in loops tudents of cell biology could be excused for thinking that laminin biology evolved purely to vex them. Multiple different laminins—combinations of ␣ , ␤ , and ␥ subunits that make up at least 15 different versions of this heterotrimeric protein—are expressed in different places at different times, making a sensible analysis of this protein family a challenge. S Most researchers have started with knockout experiments, but it is hardly surprising when a knockout defect correlates with the time and place of normal expression. Perhaps any laminin would suffice in the deleted laminin's place. Now, Kikkawa et al. (page 187) find that this is not the case. They uncover a specialized function for the laminin ␣ 5 isoform (not to be confused Mesangial cells (mc) need to bind to a specific laminin (left, white line) to help form kidney capillary loops. with laminin-5) during development of the kidney glomerular basement membrane (GBM). Laminins are key ingredients of basement membranes, which are both structural barriers and platforms for cellular interaction. GBM laminins present at the early, S-shape stage of kidney development contain the ␣ 1 subunit, but are replaced at the later capillary loop stage with ones that dendrocytes had never been investigated. Now, Belachew et al. have cultured the CNP-GFP ϩ /NG2 ϩ cells, and found that the cells quickly turn into a variety of neural cell types, including astrocytes, oligodendrocytes, and electrically active neurons. When examined in their natural context, CNP-GFP ϩ /NG2 ϩ cells are highly proliferative and give rise to a variety of …