PATTERN-FORMATION IN THE CEREBELLUM OF MURINE EMBRYONIC STEM-CELL CHIMERAS

The cerebellar cortex is subdivided into an elaborate, stereotyped arr ay of transverse zones and parasagittal stripes. It has been speculate d that (i) all Purkinje cells derive from 10 to 20 precursors allocate d early in embryogenesis and (ii) that pattern formation is based on c ell lineage restriction in the founder pool. These hypotheses have bee n tested by clonal analysis of embryonic stem cell chimeras. Neither s peculation is supported: the analysis suggests that Purkinje cells der ive from a founder population of > 10(2) precursors, and that neither cerebellar transverse developmental boundaries nor parasagittal stripe s have a clonal origin. We conclude that early lineage restriction pla ys no role in cerebellar pattern formation.