EVIDENCE IN THE MOUSE FOR SELF-RENEWING STEM-CELLS IN THE FORMATION OF A SEGMENTED LONGITUDINAL STRUCTURE, THE MYOTOME

A novel method of clonal analysis has been used in the mouse to define the cellular events that lead formation of a segmented longitudinal s tructure, myotome. Progenitor cells of the myotome were randomly marke d during development by intragenic homologous recombination in transge nic mice expressing a reporter laacZ gene. 153 clones corresponding to 7829 cells, that is 20% of the myotomal population of one embryo, mer e obtained from 3000 E11.5 embryos, Their analysis leads to the hypoth esis that, at E11.5, the 41 segments of the myotome have been mainly p roduced from a unique, spatially organised pool of self-renewing stem cells that accompanies the formation of the anterior-posterior axis.