B6. Tyrp1b GpnmbR150X mice have optic nerve phenotypes similar to standard B6 mice. Optic nerve cross-sections were stained by the PPD method, which darkly stains the myelin sheath of all axons and the axoplasm only of diseased or dying axons. The majority of optic nerves had only the mild degree of damage that is typical for aged mice, as shown here in a comparison of optic nerves from: (A) typical 22-month-old B6, versus (B) typical 22-month-old B6.Tyrp1b GpnmbR150X. This was true even in mice with the highest IOPs recorded in the study, as shown here with (C) 14-month-old B6.Tyrp1b GpnmbR150X and (D) 22-month-old B6.Tyrp1b GpnmbR150X. Scale bar = 10 μm. (E and F) The overall distribution of nerve damage was almost identical in both standard B6 and B6.Tyrp1b GpnmbR150X mice. Although some mice of each genotype developed a "moderate" degree of damage with age, the degree of damage in these mice only just met inclusion criteria for the "moderate" level and never involved significant axon loss. It was, therefore, much milder in all of these "moderate" mice than is typical of "moderate" D2 mice [42, 43]. A single B6.Tyrp1b GpnmbR150X nerve had severe damage. The similar damage distributions of both standard B6 and B6.Tyrp1b GpnmbR150X mice indicates that the damage reflects age-related B6 changes that are not related to Gpnmb and Tyrp1 glaucoma. For each group, the number of optic nerves graded for B6 and B6.Tyrp1bGpnmbR150X were: (4–6 months) 10 and 8, (11–12 months) 19 and 22, (13–15 months) 29 and 38, (16–19 months) 28 and 28, (20–26 months) 24 and 17. (E) Quantitative axon counts (mean ± SEM) show no detectable axon loss in B6.Tyrp1b GpnmbR150X compared with standard B6 mice. The similar damage distributions and lack of axon loss in both strains indicates that the detected damage reflects age-related B6 changes that are not related to Gpnmb and Tyrp1 glaucoma. For each group, the number of randomly selected nerves utilized in quantitative axon counting for B6 and B6.Tyrp1bGpnmbR150X were: (4- months) 6 and 6, (22–27 months) 8 and 10.
Anderson et al. BMC Biology 2006 4:20 doi:10.1186/1741-7007-4-20