EGF-responsive neural stem cells are a transient population in the developing mouse spinal cord

The adult mouse forebrain, which exhibits substantial ongoing cell genesis, contains self-renewing multipotent neural stem cells that respond to epide rmal growth factor (EGF), but the adult spinal cord, which exhibits limited cell genesis, does not. Spinal cord development is a process characterized by defined periods of cell histogenesis. Thus, in the present study we ask ed whether EGF-responsive neural stem cells are present within the spinal c ord during development. At embryonic day (E) 11, subsequent to the onset of neurogenesis, only fibroblast growth factor (FGF) receptors and FGF-2 (req uiring heparan sulphate)-responsive stem cells are present in the spinal co rd. Between E12 and 14, at the peak of spinal cord neurogenesis and the ons et of gliogenesis, EGF receptors appear along with clonally derived highly expandable EGF-responsive neural stem cells. Following the cessation of cel l histogenesis, the adult spinal cord is largely devoid of both EGF recepto rs and EGF-responsive stem cells. On the other hand, the FGF receptor1c sub type and multipotent FG F-2-responsive neural stem cells are present in ear ly development and in the adult. The order of appearance of spinal cord neu ral stem cells and in vitro lineage analysis suggests that a more primitive FGF-2-responsive stem cell produces the EGF-responsive stem cell. These fi ndings suggest that EGF-responsive neural stem cells appear transiently in the spinal cord, during the peak period of cell histogenesis, but are no lo nger present in the relatively quiescent adult structure.