Temperature-Dependent Regulation of PLP/DM20 and CNP Gene Expression in Two Conditionally-Immortalized Jimpy Oligodendrocyte Cell Lines

We conditionally immortalized jimpy primary oligodendrocytes (ODCs) with the temperature-sensitive SV40 large T antigen. Two cell lines (clones JP1.1 and JP1.2) were generated that expressed a number of ODC markers. Both jimpy cell lines expressed DM20 mRNAs at the proliferative temperature of 34°C, but not at the “differentiation” temperature of 39°C. Interestingly, at 39°C neither cell line appeared to differentiate further, and neither survived longer than 7 days, in contrast to other ODC cell lines from normal animals that survive many weeks at 39°C. These findings are not consistent with the notion that a PLP/DM20 gene product is the cause of oligodendrocyte cell death in jimpy, since neither jimpy cell line survived at 39°C, and neither line expressed PLP or DM20 proteins. Analysis of the expression of the CNP (2′3′ cyclic nucleotide-3′-phosphodiesterase) gene indicated that in both cell lines only one of the two CNP isoforms was expressed at 34°C. Raising the temperature to 39°C caused a greater reduction in the levels of CNP protein than CNP mRNA. Taken together, the DM20 and CNP data suggest that at least some of the decline in myelin/oligodendrocyte components observed in jimpy brains may not be due simply to fewer mature oligodendrocytes, but also to a down regulation of expression of these genes at several levels including transcriptional and post-transcriptional events. Our results provide two cell models for in vitro investigations into the nature of the jimpy mutation at several cellular and molecular levels.