Cycling cells in the adult rat neocortex preferentially generate oligodendroglia

Gliogenesis in the mammalian central nervous system does not cease abruptly like neurogenesis, Instead, glia accumulate over a time period that extend s into adulthood. To determine whether new glial cells in the adult cortex arise from resident progenitors and to determine the glial types to which t hese progenitors give rise to, cells in the perinatal subventricular zone ( SVZ) were labeled with replication-deficient retroviral vectors, and clonal clusters of glia in the neocortex were examined from 1 week to 8 months of age, The average clonal cluster size increased during the first month of l ife. Interestingly, clusters containing oligodendrocyte lineage cells prefe rentially expanded with age, on average doubling every 3 months. Unexpected ly, the number of cells in astrocyte clusters decreased over time. In heter ogeneous clusters, the numbers of oligodendroglia increased, whereas the nu mber of astrocytes did not, Moreover, clonal clusters containing mature gli a also contained less mature cells, indicating that clonally related progen itors do not differentiate synchronously in vivo. Thus, progenitors from th e SVZ continue to cycle, resulting in an accumulation of oligodendroglia in the neocortex, These slowly cycling cells likely express the NG2 proteogly can because a subset of the clonal clusters contained NG2(+) cells and thes e NG2(+) cells accumulated with time. (C) 1999 Wiley-Liss, Inc.