Gliogenesis depends on glide/gcm through asymmetric division of neuroglioblasts

Some neurons and glial cells originate from neuroblasts and glioblasts, ste m cells that delaminate from the ectoderm of developing ny embryos. A secon d class of glial cells and neurons differentiates from multipotent precurso rs, the neuroglioblasts. The differentiation of both glial cell types depen ds on glial cell deficient/glial cell missing (glide/gcm). Although it has been shown that this transcription factor promotes gliogenesis at the expen se of neurogenesis, the cellular mechanisms underlying this fate choice are poorly understood. Using loss and gain of function glide/gcm mutations her e we show that the cell fate choice takes place in the neuroglioblast, whic h divides and produces a glioblast and a neuroblast. Such choice requires t he asymmetric distribution of glide/gcm RNA, which accumulates preferential ly on one side of the neuroglioblast and is inherited by one cell, the pres umptive glioblast. Interestingly, glial cells can differentiate from cells that delaminate as neuroglioblasts or they can arise from cells that start expressing glide/gcm several hours after delamination of a neuroblast. Alto gether, these findings identify a novel type of asymmetric cell division an d disclose the lineage relationships between glia and neurons. They also re veal the mode of action of the glide/gcm promoting factor. (C) 1999 Academi c Press.