Inbred strains of mice differ in susceptibility to atherogenesis when challenged with a high fat, high cholesterol diet containing 0.5% cholic acid. Studies of recombinant inbred (RI) strains derived from the susceptible strain C57BL/6J (B6) and the resistant strains C3H/HeJ (C3H) and BALB/cJ have revealed an association between fatty streak lesion size and a decrease in high density lipoprotein (HDL) levels on the diet. To better understand the genetic factors contributing to HDL metabolism and atherogenesis in response to the diet, we studied mice derived from an intercross between B6 and C3H using a complete linkage map approach. A total of 185 female progeny were typed for 134 genetic markers spanning the mouse genome, resulting in an average interval of about 10 cM between markers. A locus on distal chromosome 1 containing the apolipoprotein AII gene was linked to HDL-cholesterol levels on both the chow and the atherogenic diets, but this locus did not contribute to the decrease in HDL-cholesterol in response to the diet. At least three distinct genetic loci, on chromosomes 3, 5, and 11, exhibited evidence of linkage to a decrease in HDL-cholesterol after a dietary challenge. Since a bile acid (cholic acid) is required for the diet induced changes in HDL levels and for atherogenesis in these strains, we examined cholesterol-7-alpha hydroxylase (C7AH) expression. Whereas B6 mice exhibited a large decrease in C7AH mRNA levels in response to the diet, C3H showed an increase. Among the intercross mice, multiple loci contributed to the regulation of C7AH mRNA levels in response to the diet, the most notable of which coincided with the loci on chromosomes 3, 5, and 11 controlling HDL levels in response to the diet. None of these loci were linked to the C7AH structural gene which we mapped to proximal chromosome 4. These studies reveal coordinate regulation of C7AH expression and HDL levels, and they indicate that the genetic factors controlling HDL levels are more complex than previously suggested by studies of RI strains. Furthermore, we observed that two of the loci for C7AH expression contributed to differences in gall-

Calcium deposition at sites of inflammation and necrosis is a fundamental but poorly understood element of the response of tissue to injury. It is evident in clinical diseases, including atherosclerosis and cardiac valve sclerosis, in which chronic inflammation or degenerative process with cell death is involved. In the presence of normal calcium and phosphate serum concentrations, such calcification is usually termed dystrophic calcification or calcinosis. Ultrastructural studies have shown that the initial events include cell necrosis and granular calcium deposition in or around the mitochondria (1-3). The pivotal role of intracellular calcium concentrations for cell injury and necrosis has been established (4, 5) and recent data also suggest the involvement of cellular calcium homeostasis in the pathogenesis of chronic myocarditis and cardiomyopathy (6-8).Age-related spontaneous dystrophic cardiac calcinosis (DCC) occurs in several inbred strains of mice, including BALB/c, DBA/2, and C3H; DCC may even lead to congestive heart failure in older animals (9-12). Apart from age and genetic background, other factors including infectious agents (13-15), sex (9, 12), hormonal status (9,(16)(17)(18), and diet (1, 9, 19-21) can markedly influence the time of onset and the severity of DCC. The factors involved in the various etiologies of DCC are different, yet a common element of each is cell injury, necrosis, and subsequent calcium deposition. The typical pattern of susceptibility to DCC was also observed following a standardized myocardial freeze-thaw injury, suggesting a common genetic basis independent from the nature of the etiology (22).We now report the mapping of a major gene determining DCC, designated Dyscalc, on proximal mouse chromosome 7. The locus was identified by quantitative trait locus (QTL) analysis of an F2 intercross between the susceptible strain C3H/HeJ and the resistant strain C57BL/6J using a complete linkage map approach. The significance of the QTL results was tested by permutation analysis and the map position was further confirmed by analysis of a set of recombinant inbred (RI) strains derived from these progenitor strains. The results have implications for the understanding of cell injury and necrosis in myocardial and cardiovascular diseases. MATERIALS AND METHODSAnimals. All mice were obtained from The Jackson Laboratory. An F2 intercross between inbred strains C57BL/6J and C3H/HeJ was constructed in our laboratory; only female progeny (n = 197) were included in the studies to eliminate gender differences as a potential confounder. All animals were maintained in pathogen-free facilities on a 12-hr light/12-hr dark cycle with free access to water and food throughout the experimental period. At 3 months of age, mice were placed on a high-fat, high-cholesterol diet (TD 90221; Harlan-Teklad, Madison, WI) to accelerate DCC (23). After 8 weeks of high-fat diet, mice were sacrificed by cervical dislocation.Histological Analyses. After the mice were killed, the heart and proximal aorta were exci...

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Reversible tyrosine phosphorylation is integral to the process of oligodendrocyte differentiation. To interfere with the subset of the phosphorylation cycle overseen by protein tyrosine phosphatase epsilon (PTP epsilon) in oligodendrocytes, we applied a substrate-trapping approach in the development of transgenic mice overexpressing a catalytically inactive, transmembrane PTP epsilon-hemaglutinin (tm-PTP epsilon-HA) from the dual promoter element of the gene encoding the myelin protein 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP). Transgene expression peaked during the active myelinating period, at 2-3 weeks postnatal. Two tyrosine phosphoproteins, alpha-enolase and beta-actin, were phosphorylated to a greater degree in transgenic mice. Despite a high degree of tm-PTP epsilon-HA expression, myelin was grossly normal in nearly all axonal tracts. Phenotypic abnormalities were limited to optic nerve, where a decrease in the degree of myelination was reflected by reduced levels of myelin proteins on postnatal day 21 (PND21), as well as a decrease in the density of differentiated oligodendrocytes. The optic chiasm was reduced in thickness in transgenic mice; optic nerves similarly exhibited a reduction in transverse width. Further analyses of the optic pathway demonstrated that transgenic protein was unexpectedly present in retinal ganglion cells, whose axons are the targets of myelination by optic nerve oligodendrocytes. On PND28, transgenic protein declined dramatically in both oligodendrocytes and retinal ganglion cells contributing to the recovery of optic nerve myelination. Thus, delayed myelination arises only when tm-PTP epsilon-HA is simultaneously expressed in myelin-forming glia and their neuronal targets. While tm-PTP epsilon related signaling pathways may figure in axon-glial interactions, interfering with tm-PTP epsilon activity does not perceptibly affect the development or myelinating capacity of most oligodendrocytes.