Dorsal Subventricular Zone Research Articles

Mash1 specifies neurons and oligodendrocytes in the postnatal brain

Progenitors in the telencephalic subventricular zone (SVZ) remain mitotically active throughout life, and produce different cell types at embryonic, postnatal and adult stages. Here we show that Mash1, an important proneural gene in the embryonic telencephalon, is broadly expressed in the postnatal SVZ, in progenitors for both neuronal and oligodendrocyte lineages. Moreover, Mash1 is required at birth for the generation of a large fraction of neuronal and oligodendrocyte precursors from the olfactory bulb. Clonal analysis in culture and transplantation experiments in postnatal brain demonstrate that this phenotype reflects a cell-autonomous function of Mash1 in specification of these two lineages. The conservation of Mash1 function in the postnatal SVZ suggests that the same transcription mechanisms operate throughout life to specify cell fates in this structure, and that the profound changes in the cell types produced reflect changes in the signalling environment of the SVZ.

Transient populations of presumptive macrophages in the brain of the developing hamster, as indicated by endocytosis of blood-borne horseradish peroxidase

During postnatal development, clusters of cells associated with the mononuclear phagocytic system appear within the white matter of rodents and cats. We studied the distribution and morphology of these cells in the hamster's brain during the first 2 weeks after birth. In animals of different ages, horseradish peroxidase was injected into the heart. After 3–6 h survival, the animals were perfused with aldehydes and had their brains removed, cut and reacted. In another series, fixed brain sections from horseradish peroxidase-injected and non-injected animals were reacted for a non-specific esterase expressed by monocytes and macrophages. The horseradish peroxidase reaction-product was seen throughout the nervous tissue at the first potnatal day, appearing more concentrated in certain brain sectors from postnatal day 3 through 10, to finally become restricted to a few regions at postnatal day 16. Horseradish peroxidase-labeled cells appeared in increasing numbers from postnatal day 1 to 8. decreasing thereafter to disappear completely at postnatal day 16. Some labeled cells were roundish or elliptical with few, if any, processes; others had several clearly detectable processes. Horseradish peroxidase-labelled cells formed clusters within the dorsal subventricular zone, dorsal cortical white matter, corpus callosum and several other prosencephalic fiber tracts. The morphology of esterase-reactive cells was less clearly outlined but their distribution and relative density correlated with those of horseradish peroxidase-labeled cells. Also, many horseradish peroxidase-labeled cells were esterase-positive in most clusters. We conclude that 1. (1) some cells in the developing brain selectively endocytose and accumulate blood-borne horseradish peroxidase in their cytoplasm, 2. (2) these cells do not appear to be neurons but a particular cell type associated to the mononuclear phagocytic system and 3. (3) they cluster transiently in particular sectors of the cortical and subcortical white matter during the first 2 weeks after birth.