ИСТИНА

In the developing and adult nervous system, neural stem and progenitor cells divide in restricted regions and their progenies migrate along complex trajectories to reach distant areas of the brain. Until now, 3D organization of neurogenic zones and pathways of cell migration has remained undisclosed. Recent years were marked by the active development of 3D microscopy techniques which may reveal hidden patterns and dynamics in neurogenic zones not recognized on conventional flat sections. In this study, we developed the new pipeline for 3D and 4D visualization and analysis of cell division and migration in the whole brain, based on the labeling of dividing cells with 5-ethynyl-2'-deoxyuridine (EdU) and detecting them with fluorescent azide using whole-mount click-reaction (WM-CLICK) and light-sheet microscopy. Using this pipeline, we observed uneven distribution of EdU+ cells in adult subventricular zone (SVZ) and found regions with high cell density forming three stripes, which merge together into rostral migration stream (RMS). Using an interval pulse labeling paradigm, we observed the displacement of the density of labeled cells from SVZ towards olfactory bulb (OB). Three stripes in the V-SVZ were not visible clearly 2h after EdU injection and they appeared only in 24 h. In 120 h after labeling, almost all EdU+ cells were located in OB. Thus, high cell density stripes in SVZ correspond to three migration branches which have not been previously described. We also discovered two distinct segments of RMS with different proliferative potential - the anterior segment of RMS consisted migrating but not dividing cells. Finally, we visualized and analyzed patterns of dividing cells in perinatal brain and found dynamics of cell migration differ from adults.