Clonal development of the retinal epithelium in mouse chimaeras and X-inactivation mosaics

ABSTRACT A comparative study of coherent clones in the retinal epithelium is presented for mouse aggregation chimaeras and X-inactivation mosaics. There is a basic similarity in the number of coherent clones and the pattern of clonal development between mosaics and chimaeras. While this similarity is compatible with the difference in mean patch size reported by other authors this is at variance with some interpretations of previous work and suggests that no conclusive evidence on the timing of X-inactivation is provided by comparisons of patch sizes between chimaeras and mosaics. The present clonal analysis also suggests that at days post coitum the cells in the retinal epithelium are distributed almost randomly while, in the adult, the cells are grouped into small coherent clones, which comprise an average of five or six nuclei. However, these data could also be explained by larger, irregular coherent clones.