Figure 6. Neonatal myelinating cells dedifferentiate slowly in the absence of c-Jun. (A and B) Comparison of P0 expression in control cells from c-Junfl/fl/CRE−(cJun con) mice and cells without c-Jun from c-Junfl/fl/CRE+ (cJun null) mice prepared at P5 and cultured in DM containing 20 ng/ml NRG-1 for 4 d. (A) Cells with high myelination-related levels of P0 have largely disappeared from control cultures. (B) c-Jun–null cultures retain numerous cells with high P0, two of which are illustrated. (C–F) Similar delay in the loss of periaxin in cells prepared at P2 from nerves of cJun–null mice cultured for 2 d (see Materials and methods). (C and D) Control cultures are c-Jun positive and periaxin has largely disappeared. (E and F) c-Jun–null cultures are c-Jun negative and retain a large number of strongly periaxin-positive cells. (G and H) Similar experiments with cells from JunAA mice. These cells lose periaxin expression at the same rate as control cells, indicating that the major N-terminal phosphorylation sites of c-Jun are not needed for suppression of periaxin. Bar, 15 μm. (I) Quantification of the results illustrated in C–H. The graph shows the number of periaxin-positive cells (relative to the number 3 h after plating) in c-Jun control, c-Jun–null and JunAA cells after 2, 4, and 6 d in DM ± 20 ng/ml NRG-1. (J) mRNA for myelin genes disappears only slowly from c-Jun–null cells. Schwann cells purified from control, c-Jun–null, and JunAA P3 mice were plated for 48 h in DM before RNA was extracted and levels of myelin markers were analyzed by quantitative PCR. Relative expression levels of c-Jun, MBP, periaxin, and P0 (MPZ) were obtained by normalizing samples to GAPDH. The data were then expressed as a percentage of the maximum (1) for each of the four genes. The difference in MBP, P0, and periaxin mRNA levels between c-Jun control and null mice was significant (P < 0.01). The same applies to the differences between JunAA and null mice. The dataset for each gene was analyzed by one-way ANOVA and Tukey's Multiple Comparison test where appropriate (using GraphPad Prism Software). Error bars show one standard deviation of the mean. AU, arbitrary units.
Figure 6.

Neonatal myelinating cells dedifferentiate slowly in the absence of c-Jun. (A and B) Comparison of P0 expression in control cells from c-Junfl/fl/CRE−(cJun con) mice and cells without c-Jun from c-Junfl/fl/CRE+ (cJun null) mice prepared at P5 and cultured in DM containing 20 ng/ml NRG-1 for 4 d. (A) Cells with high myelination-related levels of P0 have largely disappeared from control cultures. (B) c-Jun–null cultures retain numerous cells with high P0, two of which are illustrated. (C–F) Similar delay in the loss of periaxin in cells prepared at P2 from nerves of cJun–null mice cultured for 2 d (see Materials and methods). (C and D) Control cultures are c-Jun positive and periaxin has largely disappeared. (E and F) c-Jun–null cultures are c-Jun negative and retain a large number of strongly periaxin-positive cells. (G and H) Similar experiments with cells from JunAA mice. These cells lose periaxin expression at the same rate as control cells, indicating that the major N-terminal phosphorylation sites of c-Jun are not needed for suppression of periaxin. Bar, 15 μm. (I) Quantification of the results illustrated in C–H. The graph shows the number of periaxin-positive cells (relative to the number 3 h after plating) in c-Jun control, c-Jun–null and JunAA cells after 2, 4, and 6 d in DM ± 20 ng/ml NRG-1. (J) mRNA for myelin genes disappears only slowly from c-Jun–null cells. Schwann cells purified from control, c-Jun–null, and JunAA P3 mice were plated for 48 h in DM before RNA was extracted and levels of myelin markers were analyzed by quantitative PCR. Relative expression levels of c-Jun, MBP, periaxin, and P0 (MPZ) were obtained by normalizing samples to GAPDH. The data were then expressed as a percentage of the maximum (1) for each of the four genes. The difference in MBP, P0, and periaxin mRNA levels between c-Jun control and null mice was significant (P < 0.01). The same applies to the differences between JunAA and null mice. The dataset for each gene was analyzed by one-way ANOVA and Tukey's Multiple Comparison test where appropriate (using GraphPad Prism Software). Error bars show one standard deviation of the mean. AU, arbitrary units.

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