NOTOCHORD AND FLOOR PLATE STIMULATE OLIGODENDROCYTE DIFFERENTIATION IN CULTURES OF THE CHICK DORSAL NEURAL-TUBE

The regionalization of oligodendrocyte potentialities and the cellular interactions leading to the expression of the oligodendrocyte phenoty pe have been analyzed in the embryonic chick spinal cord, Dorsal and v entral regions of the spinal cord of 4-day-old embryos (E4) were culti vated separately, Oligodendrocyte differentiation was monitored at var ious times after explantation, using specific oligodendrocyte markers, After 2 weeks, several hundreds of differentiated oligodendrocytes we re invariably observed in ventral cultures whereas significant numbers of oligodendrocytes failed to develop in dorsal spinal cord cultures, However, the E7 dorsal spinal cord was found to produce large numbers of oligodendrocytes, indicating that the ventral restriction of oligo dendrocyte potentialities is transient, To test whether ventrally deri ved signals might influence oligodendrocyte differentiation, E4 dorsal spinal cord microexplants were cocultivated with notochord segments o r with floor plate tissue. Numerous oligodendrocytes were found in dor sal explants associated with either tissue, notochord or floor plate, but not in dorsal explants cultivated alone, indicating that cells com petent to be induced along the oligodendrocyte phenotype exist in the dorsal spinal cord, These results show that oligodendrocyte differenti ation potentialities are initially restricted to the ventral spinal co rd and suggest that ventrally derived signals from notochord and floor plate influence oligodendrocyte differentiation in the embryonic spin al cord. (C) 1995 Wiley-Liss, Inc.