Alteration of the primary pattern of central myelin in a chimaeric environment--study of shiverer----wild-type chimaeras.

Using chimaeras produced from the shiverer mutant with a BALB/C background (white coat color) and normal mice of the C57BL/6N strain (black coat color) by the aggregation method, the morphological patterns of the central myelin sheaths were examined by electron microscopy, with special reference to the structure of the myelin lamellae of the one genotype in an environment dominated by the other genotype. The results obtained may be summarized as follows. The oligodendrocytic processes of both genotypes are able to interact independently with the axon unrelated to its genotype. The lamellar structure of the myelin sheath, i.e., whether or not it is composed of alternating major dense and intraperiod lines, is primarily determined by the genotypes of the oligodendrocytes concerned. The processes of shiverer oligodendrocytes can spirally enwrap axons in the chimaeric CNS which shows dominance of the normal genotype. In contrast, in the environment of shiverer dominance, the spiral arrangement of the oligodendrocytic processes of the normal genotype is often disturbed, probably by the oligodendrocytic processes of the shiverer genotype. Thus, the primary pattern of the myelin sheaths can be altered under the chimaeric condition, and the formation of the myelin sheaths depends essentially on the behavior of the oligodendrocytic processes, which is determined by the genetic specificity.