Most of the cells of the mammalian retina are terminally differentiated, and do not regenerate once fully developed. This implies that these cells have strict controls over their metabolic processes, including protein turnover. We report the use of metabolic labelling procedures and secondary ion mass spectrometry imaging to examine nitrogen turnover in retinal cells, with a focus on the outer nuclear layer, inner nuclear layer, and outer plexiform layer. We find that turnover can be observed in all cells imaged using NanoSIMS. However, the rate of turnover is not constant, but varies between different cellular types and cell regions. In the inner and outer nuclear layers, turnover rate is higher in the cytosol than in the nucleus of each cell. Turnover rates are also higher in the outer plexiform layer. An examination of retinal cells from mice that were isotopically labeled very early in embryonic development shows that proteins produced during this period can be found in all cells and cell regions up to 2 months after birth, even in regions of high turnover. Our results indicate that turnover in retinal cells is a highly regulated process, with strict metabolic controls. We also observe that turnover is several-fold higher in the synaptic layer than in cell layers. Nevertheless, embryonic proteins can still be found in this layer 2 months after birth, suggesting that stable structures persist within the synapses, which remain to be determined.

中文翻译：

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NanoSIMS 对小鼠视网膜细胞的观察揭示了对氮周转的严格代谢控制

哺乳动物视网膜的大多数细胞是终末分化的，一旦完全发育就不会再生。这意味着这些细胞对其代谢过程有严格的控制，包括蛋白质周转。我们报告使用代谢标记程序和二次离子质谱成像来检查视网膜细胞中的氮周转，重点是外核层、内核层和外丛状层。我们发现在使用 NanoSIMS 成像的所有细胞中都可以观察到周转。然而，周转率不是恒定的，而是在不同细胞类型和细胞区域之间变化。在内核层和外核层中，每个细胞的细胞质中的周转率高于细胞核中的周转率。外丛状层的周转率也更高。对胚胎发育早期被同位素标记的小鼠视网膜细胞的检查表明，在此期间产生的蛋白质可以在出生后长达 2 个月的所有细胞和细胞区域中找到，即使在高周转区域也是如此。我们的结果表明，视网膜细胞的更新是一个高度受管制的过程，具有严格的代谢控制。我们还观察到突触层的周转率比细胞层高几倍。尽管如此，在出生 2 个月后仍可在该层中发现胚胎蛋白，这表明突触内仍然存在稳定的结构，这仍有待确定。即使在高周转地区。我们的结果表明，视网膜细胞的更新是一个高度受管制的过程，具有严格的代谢控制。我们还观察到突触层的周转率比细胞层高几倍。尽管如此，在出生 2 个月后仍可在该层中发现胚胎蛋白，这表明突触内仍然存在稳定的结构，这仍有待确定。即使在高周转地区。我们的结果表明，视网膜细胞的更新是一个高度受管制的过程，具有严格的代谢控制。我们还观察到突触层的周转率比细胞层高几倍。尽管如此，在出生 2 个月后仍可在该层中发现胚胎蛋白，这表明突触内仍然存在稳定的结构，这仍有待确定。