In vivo analysis of cell lineage in vertebrate neurogenesis

Abstract

One of the key processes in building the nervous system is the assignment of cell phenotype. Experiments in culture and in some amenable organisms have provided evidence for a wide variety of developmental strategies that generate the diverse phenotypes in the mature nervous system. These range from a strict, autonomous control of cell fate in which the precursors dictate the phenotype(s) of their progeny, to a much looser, conditional scheme in which interactions of the cells with their environment play a major role in their selection of phenotype. A first step towards analyzing the control of cell fate is to define the set of phenotypes to which a single precursor can give rise. Although this goal sounds simple, meeting this challenge has been difficult because many of the key events take place in large, apparently homogeneous populations of cells. To circumvent this problem, recent experimental designs have utilized techniques to make individual cells distinct from one another, making it possible to follow single precursor cells and their progeny unambiguously over time. Either integration of a marker gene by a retrovirus or microinjection of a vital dye with a micropipette render a precursor uniquely identifiable; because these markers are inherited by its descendants at mitosis, such approaches make the family tree of one precursor discernable from the mass of other unlabelled cells. Although none of the techniques is free from flaws, they are generating useful data on cell lineages and movements during neuronal development. The results collected to date suggest that there is no single developmental program that is common to all systems; instead, a blend of different developmental strategies are utilized in different regions of the developing nervous system.