Academic Background

BA., Radcliffe College, 1965
PhD, Harvard University, 1971

Development genetics, experimental study of myelin, cytological and ultrastructural methods

The CNS myelin sheath is a specialized outgrowth of the oligodendrocyte plasma membrane which forms a multilamellar sleeve of characteristic ultrastructural morphology and biochemical composition enclosing an axon. Mutations in the genes encoding the two major myelin proteins + myelin basic protein (MBP) and proteolipid protein (PLP) + each produce specific defects in oligodendrocyte/myelin development and morphology as well as in the amount of the respective structural proteins. When these and/or other CNS myelin mutations are combined in double mutant mice, we have found that the defects in development or morphology are often altered separately from the protein levels. These unexpected intergenic interactions suggest that:

1. The wild-type MBP gene has at least two separately regulated functions.
2. The wild-type PLP gene has at least three such independent functions.
3. When major myelin proteins are lacking, the oligodendrocyte may make myelin-like sheaths using other proteins + minor, transient, or non-specific.
4. Some function of the MBP gene may be toxic to oligodendrocytes unless it is complemented by the proper function of the PLP gene.

We are exploring and testing these ideas in our laboratories. One aspect of our work involves a new sex-linked lethal mouse myelin mutation (named jp^4j), which we believe to be in the PLP gene. We are currently characterizing the mutation by sequencing the PLP gene of the jp^4j mouse, studying the morphology of its oligodendrocytes and myelin by light and electron microscopy, and determining steady-state levels of myelin-specific mRNA’s and proteins by Northern and immunoblots. These studies should yield important new information about the relationship between location of mutations in the PLP gene and specific impairments of gene functions. They will also be helpful in better understanding how PLP protein is actually integrated into the myelin membrane. Another aspect of our work involves the multidisciplinary analysis of the molecular, biochemical, and quantitative morphological phenotypes of specific double mutant mice. Genes from which these combinations are being engineered include two MBP mutations, an MBP transgene, three PLP mutations, as well as the new putative PLP mutation which we are characterizing. Specific phenotypes are being defined in both the intact CNS and in the simplified environment of dispersed oligodendrocyte cultures.

The goal of this work is to gain new insights into normal myelin gene expression and the roles of specific proteins in CNS myelination. These studies may also provide information applicable to myelin disease in humans.