Cell-tracing Analysis for Progenitor Cell Migration in the Embryonic Dentate Gyrus
Hiroshi Shinohara 1), Toru Sato 1), Keiko Toda 1), Seiji Shioda 2), Tatsunori Seki 1)
1) Dept Histol. Neuroanat., Tokyo Medical University, Tokyo, Japan 2) Dept Anat., Showa University Sch. Med., Tokyo, Japan

In general, neurogenesis occurs during embryonic and early postnatal stages, and ceases at adult stage. However, the dentate gyrus (DG) continues neurogenesis from embryonic to adult stages, although there is a distinct neurogenic pattern between two stages. In the adult DG, granule neurons are generated in the subgranular zone, while during embryonic period, dentate neural progenitors are initially produced in the ventricular zone (VZ) close to the fimbria, and then migrate through the suprafimbrial region to the subpial region (SP) where a new proliferative zone is formed to develop the presumptive dentate gyrus. During the migration, the progenitors differentiate into granule neurons or maintain property of neural progenitors that further contribute to perinatal and postnatal neurogenesis. Although the migration of the neural precursors and relocation of the region of neurogenesis are key processes for the formation of the DG, the exact temporal and spatial patterns are still unknown. To address the problem, we performed cell-tracing analysis by in utero electroporation of RFP that were introduced into the neuroepithelium of the medial cortex. RFP-positive cells originated from the VZ migrated to the DG within 2-3 days. Immunohistochemical studies revealed that the RFP+/Tbr2+ cells were present in the SP, whereas the RFP+/Sox2+ cells were localized in both the SP and the hilus. Moreover, we performed time-lapse imaging in cultured hippocampal slices and found two groups of cell migration in the DG: ventral (pia walking cells) and dorsal dentate migration (Hippocampal fissure-touching and/or Somal translocation-like cells). We will discuss possibility that the correlation between cell-type specification and modes of cell migration.