Myelin deficient (shimld) mutant allele: morphological comparison with shiverer (shi) allele on a B6C3 mouse stock.

A new B6C3 stock of shimld mutant mice is compared in terms of behavior and CNS morphology with both a B6C3 shi stock and reports on other shimld animals. Defects of B6C3 shimld myelination seen at postnatal day 21 (P-21) are comparable to those in B6C3 shi with respect to % axons myelinated, sheath thickness, errors in the wrapping and targeting of myelin and abnormal oligodendrocyte shape. The two mutations are similarly expressed in cerebellar organotypic cultures. However, the major dense line (MDL) is present in a few shimld myelin sheaths at P-21 and a few sheaths show myelin basic protein by immunocytochemistry, while neither phenomenon is seen in shi at this age in the same CNS regions. Shimld mice survive their disease significantly better than shi. The shimld stock currently under study elsewhere differs from this B6C3 stock in that MDL was reported only in older animals, and behavior and survival were severely compromised.