Physiological properties of rod photoreceptor cells in green-sensitive cone pigment knock-in mice.
Physiological properties of rod photoreceptor cells in green-sensitive cone pigment knock-in mice.
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DOI：
10.1083/jcb1781oia3
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发表时间：
2007-07
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影响因子：
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通讯作者：
K. Sakurai;A. Onishi;H. Imai;O. Chisaka;Yoshiki Ueda;J. Usukura;K. Nakatani;Y. Shichida
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文献类型：
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作者：
K. Sakurai;A. Onishi;H. Imai;O. Chisaka;Yoshiki Ueda;J. Usukura;K. Nakatani;Y. Shichida
分别负责暗视觉和明视觉的视杆和视锥感光细胞表现出彼此不同的光反应，并且含有具有独特分子特性的相似光转导蛋白。为了研究视色素的不同分子特性对感光细胞反应的贡献，我们产生了基因敲入小鼠，其中视杆视色素（视紫红质）被小鼠绿色敏感的视锥视色素（小鼠绿色）取代。小鼠绿色被成功地转运到视杆细胞外节，尽管小鼠绿色在纯合型视网膜中的表达约为野生型视网膜中视紫红质的11%。野生型和纯合子视杆细胞的单细胞记录表明，在校正细胞体积和几种信号转导蛋白水平的差异后，小鼠绿色的闪光敏感性和单光子响应比视紫红质低三到四倍。随后使用表达小鼠绿色和视紫红质E122 Q突变体的杂合视杆进行测量，其中相同视杆细胞中的这些色素由于其独特的最大吸收而可以被选择性地照射，清楚地表明小鼠绿色的光响应比视紫红质低三倍。噪声分析表明，小鼠绿色的热激活速率为1.7 × 10（-7）s（-1），比视紫红质高860倍。小鼠绿色的热激活相对于视紫红质的热激活的增加导致对于亮光的视杆光敏性仅降低4%，但预期相反会严重影响昏暗光条件下的视觉阈值。因此，视紫红质产生大的单光子响应并在黑暗中保持高热稳定性的能力是暗视觉进化所必需的因素。
Rod and cone photoreceptor cells that are responsible for scotopic and photopic vision, respectively, exhibit photoresponses different from each other and contain similar phototransduction proteins with distinctive molecular properties. To investigate the contribution of the different molecular properties of visual pigments to the responses of the photoreceptor cells, we have generated knock-in mice in which rod visual pigment (rhodopsin) was replaced with mouse green-sensitive cone visual pigment (mouse green). The mouse green was successfully transported to the rod outer segments, though the expression of mouse green in homozygous retina was approximately 11% of rhodopsin in wild-type retina. Single-cell recordings of wild-type and homozygous rods suggested that the flash sensitivity and the single-photon responses from mouse green were three to fourfold lower than those from rhodopsin after correction for the differences in cell volume and levels of several signal transduction proteins. Subsequent measurements using heterozygous rods expressing both mouse green and rhodopsin E122Q mutant, where these pigments in the same rod cells can be selectively irradiated due to their distinctive absorption maxima, clearly showed that the photoresponse of mouse green was threefold lower than that of rhodopsin. Noise analysis indicated that the rate of thermal activations of mouse green was 1.7 x 10(-7) s(-1), about 860-fold higher than that of rhodopsin. The increase in thermal activation of mouse green relative to that of rhodopsin results in only 4% reduction of rod photosensitivity for bright lights, but would instead be expected to severely affect the visual threshold under dim-light conditions. Therefore, the abilities of rhodopsin to generate a large single photon response and to retain high thermal stability in darkness are factors that have been necessary for the evolution of scotopic vision.