Fig. 3. In vivo and in vitro dentate granule cell migration/gyrus development occurred in a comparable manner. (A,D,G) Prox1 immunostaining labeled granule cells in coronal sections of E15.5 (A), E17.5 (D) and P0 (G) wild-type mice, and showed the accumulation of these cells in the developing dentate gyrus (broken outline). In addition to increasing numbers of Prox1-positive cells in the dentate, more weakly positive Prox1 cells can also be seen in the migratory stream at the E17.5 and P0 time-points. Additional Prox1-positive cells are seen in the thalamus and more weakly staining ones transiently in the cortex. (B,E,H) Prox1 immunostaining of E15.5 hippocampal slice cultures showed a comparable rate and pattern of dentate granule cell accumulation. Cultures fixed at t=0 days in vitro (B) had similar low levels of Prox1 immunoreactivity in the dentate when compared with E15.5 tissue (A). Cultures analyzed after 2 days of culturing (E) had an increased number of Prox1-positive cells in the dentate and few weakly positive cells were also seen in the migratory stream, similar to E17.5 tissue (D). This was also seen when 4 day cultures (H) were compared with P0 tissue (G). (C,F,I) The schematic (C) shows that nlslacZ retrovirus injections into the ventricular zone adjacent to the fimbria resulted in the labeling of many cells. Cultures fixed after 1 day of culturing (F) and processed for X-gal histochemistry showed that labeled cells (blue) were restricted to a region close to the site of injection. However, by 4 days in vitro (I), many labeled cells were seen in the migratory stream and within the dentate gyrus. Scale bars: 200 µm.