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Expression of the jimpy gene in the spinal cords of heterozygous female mice. I. An early myelin deficit followed by compensation

, : Expression of the jimpy gene in the spinal cords of heterozygous female mice. I. An early myelin deficit followed by compensation. Journal of Neuroscience 6(10): 2802-2812

The jimpy mutation results in severe hypomyelination throughout the CNS of hemizygous male mice. In the female carrier of the jimpy gene, partial hypomyelination is predicted as a consequence of genetic mosaicism resulting from random X-chromosome inactivation. The spinal cord of the female carrier was studied morphologically to determine (1) if hypomyelination is present, (2) the manner in which a possible myelin deficit is expressed, and (3) the extent, if any, of compensation. The spinal cord of 14- to 15-d-old heterozygotes were found to be hypomyelinated. A deficit of 31% in the amount of myelin as compared to controls was detected in these young carriers by point-counting stereology. By the end of the first month the deficit was 12%, and after the fifth month complete recovery had occurred. These results demonstrate that the neuroglial cells are capable of compensating totally for the jimpy defect over a several month period. The reduction in the amount of myelin at 2 weeks postnatally is due to the ensheathment of fewer axons than normal and the formation of myelin sheaths that are thinner than normal. It is not due to a significant reduction in amount of axoplasm and a corresponding decrease in amount of myelin. This finding indicates that overall brain development is not retarded but that expression of the jimpy gene selectively affects the glial cells. Our morphologic studies also suggest that the neuron is not the target of the jimpy mutation. One line of evidence for this statement is that virtually all the axons are partially ensheathed, a condition that should not occur if 50% of the neurons are defective in the mosaic. The coexistence of both normal and defective cells within the same cell population and the apparent sparing of the neuron makes the female carrier of the jimpy gene an excellent model for studying mechanisms of compensation and plasticity of neuroglial cells.

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Accession: 005432074

PMID: 3760935

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Related references

Bartlett, W.P.; Skoff, R.P., 1989: Expression of the jimpy gene in the spinal cords of heterozygous female mice. 2. Oligodendroglial and endothelial cell hyperplasia. The jimpy mutation is characterized by a severe deficiency of myelin formation throughout the central nervous system of hemizygous male mice. The female carrier of the jimpy gene is also hypomyelinated, but the myelin deficit in the female is less...

Rosenfeld, J.; Friedrich, V.L., 1984: Hypomyelination and recovery of the myelin deficit in heterozygous jimpy mice. The myelin content of the anterior commissure in female carriers of the jimpy gene (X(+)X(jp)) and in normal male mice (X(+)Y) was determined using morphometric methods. Young jimpy heterozygotes (X(+)X(jp)), 42-43 days old, exhibit a 33% reductio...

Bartlett W.P.; Skoff R.P., 1984: Expression of mosaicism in spinal cords of jimpy heterozygous females. Society for Neuroscience Abstracts 10(1): 426

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