Shiverer jimpy double mutant mice. III. Comparison of shimld*jpmsd and shi*jp phenotypes demonstrates dissimilar interactions of allelic mutations.

Double mutant mice, which are of the genotype shimld/shimld*jpmsd/Y and therefore express both the shimld and jpmsd mutations, have a CNS myelin protein composition which resembles shimld/shimld alone but not jpmsd/Y alone. The double mutant CNS white matter morphology shows much less myelin and major dense line than either shimld/shimld or jpmsd/Y, but has other features which resemble jpmsd/Y but not shimld/shimld. In contrast, the parallel double mutant shi/shi*jp/Y, which expresses the alleles shi and jp rather than shimld and jpmsd, has already been shown to have biochemical and morphological phenotypes which are consistent with each other, both being intermediate between shi/shi and jp/Y and therefore suggesting partial reciprocal intergenic suppression (Brain Research, 374 (1986) 45-53 and 54-62). To assist in explaining the apparent inconsistencies between the biochemical and morphological phenotypes of the shimld/shimld*jpmsd/Y double mutant and between interactions of allelic mutations at the shi and jp loci, a hypothesis of multiple primary gene functions at these two loci is proposed.