Nishina Laboratory, The Jackson Laboratory, Bar Harbor, Maine 04609, USA.
Invest Ophthalmol Vis Sci. 2011 Jul 1;52(7):4703-9. doi: 10.1167/iovs.10-7077.
To determine the basis and to characterize the phenotype of a chemically induced mutation in a mouse model of retinal degeneration.
Screening by indirect ophthalmoscopy identified a line of N-ethyl-N-nitrosourea (ENU) mutagenized mice demonstrating retinal patches. Longitudinal studies of retinal histologic sections showed photoreceptors in the peripheral retina undergoing slow, progressive degeneration. The mutation was named neuroscience mutagenesis facility 12 (nmf12), and mapping localized the critical region to Chromosome 2.
Sequencing of nmf12 DNA revealed a point mutation in the c-mer tyrosine kinase gene, designated Mertk(nmf12). We detected elevated levels of tumor necrosis factor (Tnf, previously Tnfa) in retinas of Mertk(nmf12) homozygotes relative to wild-type controls and investigated whether the increase of TNF, an inflammatory cytokine produced by macrophages/monocytes that signals intracellularly to cause necrosis or apoptosis, could underlie the retinal degeneration observed in Mertk(nmf12) homozygotes. Mertk(nmf12) homozygous mice were mated to mice lacking the entire Tnf gene and partial coding sequences of the Lta (Tnfb) and Ltb (Tnfc) genes.(2) B6.129P2-Ltb/Tnf/Lta(tm1Dvk)/J homozygotes did not exhibit a retinal degeneration phenotype and will, hereafter, be referred to as Tnfabc(-/-) mice. Surprisingly, mice homozygous for both the Mertk(nmf12) and the Ltb/Tnf/Lta(tm1Dvk) allele (Tnfabc(-/-)) demonstrated an increase in the rate of retinal degeneration.
These findings illustrate that a mutation in the Mertk gene leads to a significantly slower progressive retinal degeneration compared with other alleles of Mertk. These results demonstrate that TNF family members play a role in protecting photoreceptors of Mertk(nmf12) homozygotes from cell death.
确定视网膜变性小鼠模型中化学诱导突变的基础并表征其表型。
间接检眼镜筛选发现一条 N-乙基-N-亚硝基脲（ENU）诱变鼠系显示视网膜斑。视网膜组织学切片的纵向研究表明，周边视网膜的感光细胞进行缓慢、进行性退化。该突变被命名为神经科学诱变设施 12（nmf12），并将关键区域定位到染色体 2 上。
nmf12 DNA 的测序揭示了 c-mer 酪氨酸激酶基因中的一个点突变，命名为 Mertk(nmf12)。我们检测到 Mertk(nmf12)纯合子相对于野生型对照的视网膜中肿瘤坏死因子（TNF，先前为 Tnfa）水平升高，并研究了 TNF 是否可以作为导致 Mertk(nmf12)纯合子中观察到的视网膜变性的基础，TNF 是一种由巨噬细胞/单核细胞产生的炎症细胞因子，可在细胞内发出信号导致坏死或凋亡。Mertk(nmf12)纯合子与缺乏整个 Tnf 基因和 Lta（Tnfb）和 Ltb（Tnfc）基因部分编码序列的小鼠交配。（2）B6.129P2-Ltb/Tnf/Lta(tm1Dvk)/J 纯合子不表现出视网膜变性表型，此后将其称为 Tnfabc(-/-)小鼠。令人惊讶的是，同时携带 Mertk(nmf12)和 Ltb/Tnf/Lta(tm1Dvk)等位基因（Tnfabc(-/-)）的纯合子小鼠表现出视网膜变性率增加。
这些发现表明，Mertk 基因中的突变导致与 Mertk 的其他等位基因相比，视网膜进行性退化的速度明显减慢。这些结果表明 TNF 家族成员在保护 Mertk(nmf12)纯合子的感光细胞免受细胞死亡方面发挥作用。
