Different clonal dispersion in the rostral and caudal mouse central nervous system

We have performed a systematic clonal analysis to describe the modes of gro wth, dispersion and production of cells during the development of the mouse neural system. We have used mice expressing a LaacZ reporter gene under th e control of the neuron specific enolase promoter to randomly generate LacZ clones in the central nervous system (CNS), We present evidence for (1) a pool of CNS founder cells that is not regionalized, i.e. give descendants d ispersed along the entire A-P axis, (2) an early separation between pools o f precursors for the anterior and posterior CNS and (3) distinct modes of p roduction of progenitors in these two domains. More specifically, cell grow th and dispersion of the progenitors follow a relatively coherent pattern t hroughout the anterior CNS, a mode that leads to a progressive regionalizat ion of cell fates. In contrast, cell growth of progenitors of the SC appear s to involve self-renewing stem cells that progress caudally during regress ion of the mode. Therefore, at least part of the area surrounding the node is composed of precursors with self-renewing properties and the development of the trunk is dependent on pools of stem cells regressing from A to P. T aken together with our analysis of the cell growth changes associated with neuromere formation (Mathis, L., Sieur, J., Voiculescu, O., Charnay, P. and Nicolas, J. F. (1999) Development 126, 4095-4106), our results suggest tha t major transitions in CNS development correspond to changes in cell behavi or and may provide a link between morphogenesis and genetic patterning mech anisms (i.e. formation of the body plan).