Abstract
The basic helix-loop-helix transcription factor c-Myc is a potent trigger of programmed cell death when overexpressed during late oligodendrocyte development in transgenic mice. Here we provide evidence that c-Myc can act synergistically with the Pit, Oct, Unc homeodomain transcription factor Oct-6 to produce myelin disease pathogenesis in transgenic mice. More than 70% of c-myc/Oct-6 bitransgenic mice, obtained from crosses between phenotypically normal heterozygous mice of various My (c-Myc) and Oc (Oct-6) transgenic strains that express c-myc and oct-6 transgenes under transcriptional control of the myelin basic protein gene, developed severe neurological disturbances characterized by action tremors, recurrent seizures, and premature death. Affected bitransgenic mice exhibited multiple hypomyelinated lesions in the white matter that did not stain with myelin-specific antibodies against myelin basic protein, proteolipid protein, CNPase, and myelin-associated glycoprotein. The mice also exhibited a larger number of terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling positive cells in the white matter as well as ultrastructural evidence of glial cell death and astrogliosis. These observations indicate that the myelin lesions observed in the c-myc/oct-6 bitransgenic mice result from the untimely programmed cell death of oligodendroglia and that the c-myc and oct-6 transgenes act synergistically in producing the lesions.
Highlights
Mined by a number of proteins that are expressed within the myelin-forming cells
We have previously shown that transgenic mice overexpressing Oct-6 under transcriptional control of the myelin basic protein (MBP) gene develop a nonapoptotic structural myelin abnormality, indicating that developmental regulation of Oct-6 expression is involved in the normal assembly of myelin in the central nervous system (CNS) (29)
We show that the majority of c-myc/oct-6 bitransgenic mice, obtained from crossing unaffected heterozygous mbp/c-myc and mbp/oct-6 transgenic animals, develop severe neurological disturbances, which coincide with the presence of multiple hypomyelinated lesions in the white matter as well as with an increased number of apoptotic cells in the brain
Summary
Transgenic mice were identified by slot blots, Southern blots, and PCR of DNA samples taken from the tail. After three to five washes in Hanks’ buffer, the sections were incubated for 1 h at 37 °C in Vectastain elite ABC peroxidase standard solution (Vector Laboratories), rinsed twice in Hanks’ buffer, and stained for 10 –15 min at room temperature using the aminoethylcarbazole substrate kit for horseradish peroxidase (Vector Laboratories). Tissue sections (10 m) were cut with a cryostat microtome, collected on glass slides, and fixed with methanol. Following several washes in Hanks’ buffer, the sections were incubated with appropriate secondary rhodamine-conjugated antisera (Dako, Denmark) (diluted 1:50 in Hanks’ buffer) for 30 min at 37 °C in a moist chamber. The immunoreactive proteins were visualized with the enhanced chemiluminiscence (ECL) kit from Amersham Pharmacia Biotech
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