Embryonic cortical stem cells secrete diffusible factors to enhance their survival.

Neural stem cells play major roles in brain development. The precise regulation of neural stem cell survival and proliferation is important for determining numbers of terminally differentiated neurons and glia. In this study, we demonstrate that embryonic neural stem cells positively regulate their own survival by secreting diffusible factors. Single cells isolated from embryonic day 14 (E14) rat cortices were plated at clonal densities to avoid direct cell-cell contact. Clones positive for nestin, a neural stem cell marker, were formed from single cells in the presence of basic fibroblast factor (bFGF). The numbers of viable cells and clones were markedly increased by supplementing conditioned medium (stem cell conditioned medium, SCM) prepared from dense cultures of embryonic cortical stem cells. TUNEL and LDH assays confirmed SCM-mediated survival of embryonic cortical stem cells.