Migration pathways and fate determination of progenitors in the subventricular zone

哺乳动物前脑的绝大多数神经胶质细胞是在围产期由脑室下区(SVZ)的祖细胞产生的。我们用GFP逆转录病毒标记新生大鼠前脑SVZ的祖细胞，并在P3切片上用时间推移视频显微镜观察它们的运动，以观察它们的迁移情况。我们发现了一小部分的祖细胞，这些祖细胞沿切向迁移到胼胝体(CC)，并穿过中线。这些突起保持了相对统一的形态：前导突向对侧延伸，但没有突起分支或偏离迁徙方向。净迁移需要前导突起的延长和核的移位，CC中的迁移细胞表现出这两种模式。我们证实了在P3CC内存在无髓轴突束，但未能通过CC共聚焦图像检测到任何径向定向的神经胶质突起(Vimentin或GLAST免疫标记纤维)，显示神经细丝免疫标记轴突与CC中表达GFP的祖细胞的主导突起非常接近。将DIL应用于右侧扣带核，观察胼胝体纤维的去向；标记纤维贯穿CC，到达左侧扣带回和运动区。逆转录病毒标记的细胞在P28脑中的分布和最终命运被检测。一小部分标记细胞位于对侧大脑半球，作为少突胶质细胞和星形胶质细胞，它们主要分布在扣带回和次级运动区的皮质和下层白质。这一分布模式与骨痂纤维的投射方向相吻合。因此，神经胶质前体细胞可能与无髓鞘轴突一起穿过CC迁移到对侧大脑半球。

The great majority of glial cells of the mammalian forebrain are generated in the perinatal period from progenitors in the subventricular zone(SVZ). We investigated the migration of progenitors from the neonatal(postnatal day O,PO) rat forebrain SVZ by labeling them in vivo with a GFP-retrovirus, and monitoring their movements by time-lapse video microscopy in P3 slices. We identified a small number of progenitors that migrated tangentially within the corpus callosum(CC) and crossed the midline. These retained a relatively uniform morphology : the leading process was extended toward the contralateral side, but showed no process branching or turning away from the migratory direction. Net migration requires the elongation of the leading process and nuclear translocation, and the migrating cells in the CC showed both modes. We confirmed the presence of unmyelihated axon bundles within the P3 CC, but failed to detect any radially directed glial processes(vimentin-or GLAST-immunolabeled fibers) spanning through the CC Confocal images showed a close proximity between neurofilament-immunolabeled axons and the leading process of the GFP-expressing progenitors in the CC. The destination of the callosal fibers was examined by applying Dil to the right cingulum ; the labeled fibers ran throughout the CC and reached the left cingulate and motor areas. The distribution and final fates of the retrovirus-labeled cells were examined in P28 brains. A small proportion of the labeled cells, were found in the contralateral hemisphere, where, as oligodendrocytes and astrocytes, they colonized predominantly the cortex and the underlying white matter of the cingulate and secondary motor areas. The distribution pattern appears to coincide well with the projection direction of the callosal fibers. Thus, glial progenitors migrate across the CC, presumably in conjunction with unmyelinated axons, to colonize the contralateral hemisphere.