Brzezinski Joseph A, Brown Nadean L, Tanikawa Atsuhiro, Bush Ronald A, Sieving Paul A, Vitaterna Martha H, Takahashi Joseph S, Glaser Tom
Department of Human Genetics, University of Michigan, Ann Arbor, 48109, USA.
Invest Ophthalmol Vis Sci. 2005 Jul;46(7):2540-51. doi: 10.1167/iovs.04-1123.
To determine how the absence of retinal ganglion cells (RGCs) in Math5 (Atoh7) mutant mice affects circadian behavior and retinal function.
The wheel-running behavior of wild-type and Math5 mutant mice was measured under various light-dark cycle conditions. To evaluate retinal input to the suprachiasmatic nuclei (SCN) anatomically, the retinohypothalamic tracts were labeled in vivo. To assess changes in retinal function, corneal flash electroretinograms (ERGs) from mutant and wild-type mice were compared under dark- and light-adapted conditions. Alterations in retinal neuron populations were evaluated quantitatively and with cell-type-specific markers.
The Math5-null mice did not entrain to light and exhibited free-running circadian behavior with a mean period (23.6 +/- 0.15 hours) that was indistinguishable from that of wild-type mice (23.4 +/- 0.19 hours). The SCN showed no anterograde labeling with a horseradish peroxidase-conjugated cholera toxin B (CT-HRP) tracer. ERGs recorded from mutant mice had diminished scotopic a- and b-wave and photopic b-wave amplitudes. The scotopic b-wave was more severely affected than the a-wave. The oscillatory potentials (OPs) and scotopic threshold response (STR) were also reduced. Consistent with these ERG findings, a pan-specific reduction in the number of bipolar cells and a smaller relative decrease in the number of rods in mutant mice were observed.
Math5-null mice are clock-blind and have no RGC projections to the SCN. RGCs are thus essential for photoentrainment in mice, but are not necessary for the development or intrinsic function of the SCN clock. RGCs are not required to generate any of the major ERG waveforms in mice, including the STR, which is produced by ganglion cells in some other species. The diminished amplitude of b-wave, OPs, and STR components in Math5 mutants is most likely caused by the decreased abundance of retinal interneurons.
确定Math5（Atoh7）突变小鼠中视网膜神经节细胞（RGCs）的缺失如何影响昼夜节律行为和视网膜功能。
在各种明暗循环条件下测量野生型和Math5突变小鼠的转轮行为。为了从解剖学上评估视网膜对上交叉核（SCN）的输入，对视网膜下丘脑束进行体内标记。为了评估视网膜功能的变化，比较了突变型和野生型小鼠在暗适应和明适应条件下的角膜闪光视网膜电图（ERG）。使用细胞类型特异性标记物对视网膜神经元群体的变化进行定量评估。
Math5基因敲除小鼠不能被光诱导，表现出自由运行的昼夜节律行为，平均周期（23.6±0.15小时）与野生型小鼠（23.4±0.19小时）无差异。SCN在用辣根过氧化物酶偶联霍乱毒素B（CT-HRP）示踪剂时未显示顺行标记。突变小鼠记录的ERG中，暗视a波和b波及明视b波振幅降低。暗视b波比a波受影响更严重。振荡电位（OPs）和暗视阈值反应（STR）也降低。与这些ERG结果一致，观察到突变小鼠中双极细胞数量普遍减少，而视杆细胞数量相对减少较少。
Math5基因敲除小鼠是时钟盲的，且没有RGC向SCN的投射。因此，RGC对小鼠的光诱导至关重要，但对于SCN时钟的发育或内在功能并非必需。在小鼠中产生任何主要的ERG波形都不需要RGC，包括在其他一些物种中由神经节细胞产生的STR。Math5突变体中b波、OPs和STR成分振幅的降低很可能是由视网膜中间神经元数量的减少所致。
