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The Journal of Neuroscience, August 6, 2003, 23(18):7207-7217
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Aberrant Growth and Differentiation of Oligodendrocyte Progenitors in Neurofibromatosis Type 1 Mutants
Michael R. Bennett,1
Tilat A. Rizvi,1
Saikumar Karyala,1
Randall D. McKinnon,2 and
Nancy Ratner1
1Department of Cell Biology, Neurobiology, and
Anatomy, University of Cincinnati College of Medicine, Cincinnati, Ohio
45267-0521, and 2Neurosurgery, Robert Wood Johnson
Medical School, Piscataway, New Jersey 08854
Neurofibromatosis type 1 (NF1) patients are predisposed to learning
disabilities, macrocephaly, and brain tumors as well as abnormalities on
magnetic resonance imaging that are postulated to result from abnormal
myelination. Here we show that Nf1+/- spinal cords in adult mice have
more than twofold-increased numbers of NG2+ progenitor cells. Nf1-/-
embryonic spinal cords have increased numbers of Olig2+ progenitors. Also,
cultures from Nf1 mutant embryos with hemizygous and biallelic
Nf1 mutations have dramatically increased numbers of CNS
oligodendrocyte progenitor cells. In medium that allows growth of
neuroepithelial cells and glial progenitors, mutant cells hyper-respond to
FGF2, have increased basal and FGF-stimulated Ras-GTP, and fail to accumulate
when treated with a farnesyltransferase inhibitor. Cell accumulation results
in part from increased proliferation and decreased cell death. In contrast to
wild-type cells, Nf1-/- progenitors express the glial differentiation
marker O4 while retaining expression of the progenitor marker nestin.
Nf1 mutant progenitors also abnormally coexpress the glial
differentiation markers O4 and GFAP. Importantly, Nf1-/- spinal
cord-derived oligodendrocyte progenitors, which are amplified 12-fold, retain
the ability to form oligodendrocytes after in vivo transplantation.
The data reveal a key role for neurofibromin and Ras signaling in the
maintenance of CNS progenitor cell pools and also suggest a potential role for
progenitor cell defects in the CNS abnormalities of NF1 patients.
Key words: NF1; progenitor; oligodendrocyte; FGF; brain; Ras
Received May. 5, 2003;
revised Jun. 10, 2003;
accepted Jun. 17, 2003.
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