Forward genetic screens in genetically accessible invertebrate organisms such as Drosophila melanogaster have shed light on transcription factors that specify formation of neurons in the vertebrate CNS. However, invertebrate models have, to date, been uninformative with respect to genes that specify formation of the vertebrate glial lineages. All recent insights into specification of vertebrate glia have come via monitoring the spatial and temporal expression patterns of individual transcription factors during development. In studies described here, we have taken this approach to the genome scale with an in silico screen of the Mahoney pictorial atlas of transcription factor expression in the developing CNS. From the population of 1445 known or probable transcription factors encoded in the mouse genome, we identify 12 novel transcription factors that are expressed in glial lineage progenitor cells. Entry-level screens for biological function establish one of these transcription factors, Klf15, as sufficient for genesis of precocious GFAP-positive astrocytes in spinal cord explants. Another transcription factor, Tcf4, plays an important role in maturation of oligodendrocyte progenitors.