The process in which neuroepithelial cells of the neural tube give rise to radial glial cells, specialized bipotential progenitors cells of the forebrain. Differentiation includes the processes involved in commitment of a cell to a specific fate. [ GOC:cls GOC:jid GOC:dgh http://purl.obolibrary.org/obo/go/references/0000021 GOC:dph http://www.ncbi.nlm.nih.gov/pubmed/16226447 ]