Clonal patterns of cell proliferation, migration, and dispersal in the brainstem of the chicken embryo

Retroviral-mediated gene transfer was used to study clonal patterns of proliferation, migration, and dispersal in the brainstem of the chicken embryo. Clones were generated at stages 13-17 (Hamburger and Hamilton, 1951), a period of neurogenesis in the brainstem neural tube subsequent to the formation of rhombomeres. Clones were examined in separate experiments at stages 24-27, when many neurons migrate and differentiate; at stages 28-29, when brainstem nuclei begin to form; and at stages 34-35, when brainstem nuclei are fully formed. Stages 24-29 are characterized by a general variability in proliferative kinetics and migratory behavior. Clone sizes range from 1 to 29 cells, and migration patterns range from strictly radial (i.e., normal to the ventricular surface) to combined radial and tangential (i.e., perpendicular to the radial component). There is, however, an underlying systematic variation: (1) clones exhibiting tangential migration contain on average more cells than clones exhibiting only radial migration, and (2) the proportion of tangentially migrating clones increases from medial to lateral. By stages 34-35 some individual clones have apparently dispersed to disparate neuronal groups. The regional diversity observed among clones suggests that position along the mediolateral axis may determine the proliferative potential of progenitors and the migratory behavior and subsequent dispersal of their descendants.