Hypomyelinated mutant mice: description of jpmsd and comparison with jp and qk on their present genetic backgrounds.

Hypomyelinated mutant mice are valuable natural animal systems for analysis of CNS myelin development, chemistry and diseases. One mutant, jpmsd, has never received thorough morphological description. We here describe the detailed morphology of jpmsd, compare it with well-studied jp and qk on their present genetic backgrounds, and discuss the genetic histories of all 3 mutants. Region for region, jpmsd has twice as much myelin as jp, but 1/2--1/5 as much as qk. Both jp and jpmsd have scarce oligodendrocytes, rare nodes of Ranvier, clustering of myelin segments, abnormal lipid-filled cells, frequent degenerating cells, and rare distorted myelin profiles. In contrast, qk has abnormally numerous oligodendrocytes, frequent nodes of Ranvier, no obvious myelin clustering, no lipid-filled cells, rare degenerating cells, and frequent abnormal or distorted myelin profiles. jp and jpmsd are quantitatively different, but qualitatively similar. Since its origin, the jpmsd disease has inadvertently been ameliorated by transferring the mutation to a different background. Persistent differences in the remainder of the genome might account for all remaining apparent differences between jp and jpmsd. In contrast, qk is totally dissimilar in morphology and presumably in pathophysiology.