Chimeras in the Study of Disorders of Myelination

A chimera is a living animal composed of genetically different cell populations that have been derived from more than one fertilized egg. The word “chimera” is also used at the level of genes, such as chimeric gene. The word “chimera” comes from an imaginary animal in ancient Greek mythology. Both primary and secondary chimeras provide us opportunities to study interactions among genetically different cells. It is therefore completely different from cell fusion, which results in a chromatin chimera. Detailed analyses of chimeras which were dominated by the normal genotype revealed that colonies of oligodendrocytes of the shiverer genotype were present as patches embedded in the white matter overwhelmingly occupied by normal myelin sheaths. By aggregating eight-cell-stage embryos, chimera mice were produced from the cells of normal and mutant animals. Analysis of the chimera thus formed provided information as to the primary changes that take place at the cellular level in the mutants.