PDF(Pubmed)
Abstract：
The first steps of vision take place within a stack of tightly packed disc-shaped membranes, or \'discs\', located in the outer segment compartment of photoreceptor cells. In rod photoreceptors, discs are enclosed inside the outer segment and contain deep indentations in their rims called \'incisures\'. The presence of incisures has been documented in a variety of species, yet their role remains elusive. In this study, we combined traditional electron microscopy with three-dimensional electron tomography to demonstrate that incisures are formed only after discs become completely enclosed. We also observed that, at the earliest stage of their formation, discs are not round as typically depicted but rather are highly irregular in shape and resemble expanding lamellipodia. Using genetically manipulated mice and frogs and measuring outer segment protein abundances by quantitative mass spectrometry, we further found that incisure size is determined by the molar ratio between peripherin-2, a disc rim protein critical for the process of disc enclosure, and rhodopsin, the major structural component of disc membranes. While a high perpherin-2 to rhodopsin ratio causes an increase in incisure size and structural complexity, a low ratio precludes incisure formation. Based on these data, we propose a model whereby normal rods express a modest excess of peripherin-2 over the amount required for complete disc enclosure in order to ensure that this important step of disc formation is accomplished. Once the disc is enclosed, the excess peripherin-2 incorporates into the rim to form an incisure.
摘要：
视觉的第一步发生在一堆紧密堆积的圆盘状膜中，或\'光盘\'，位于感光细胞的外段室。在杆状光感受器中，圆盘被封闭在外段内，并在其轮辋中包含称为“切口”的深压痕。在各种物种中都有证据表明，然而他们的角色仍然难以捉摸。在这项研究中,我们将传统的电子显微镜与三维电子层析成像相结合，以证明只有在椎间盘完全封闭后才形成切口。我们还观察到,在他们形成的最初阶段，圆盘不是通常描绘的圆形，而是形状高度不规则，类似于扩张的薄片。使用基因操纵的小鼠和青蛙，并通过定量质谱测量外段蛋白质丰度，我们进一步发现，切缘大小是由patterierin-2之间的摩尔比决定的，这是一种对椎间盘封闭过程至关重要的椎间盘边缘蛋白，和视紫红质,圆盘膜的主要结构部件。虽然高perpherin-2与视紫红质的比例会导致切口大小和结构复杂性的增加，低比率排除了切点形成。基于这些数据,我们提出了一个模型，通过该模型，正常棒在完整的圆盘外壳所需的量上表达适度过量的外围蛋白2，以确保完成圆盘形成的这一重要步骤。一旦光盘被封闭，多余的外周蛋白-2并入边缘以形成切缘。
