Thin (actin) and thick (myosinlike) filaments in cone contraction in the teleost retina.
Thin (actin) and thick (myosinlike) filaments in cone contraction in the teleost retina.
复制标题
硬骨鱼视网膜中圆锥收缩时的细丝（肌动蛋白）和粗丝（肌球蛋白样）。
DOI：
10.1083/jcb.78.1.227
复制
发表时间：
1978-07
影响因子：
7.8
通讯作者：
Burnside, B
中科院分区：
文献类型：
--
作者：
Burnside, B
鱼的细长视锥在光线下变短，在黑暗中伸长。光诱导的视锥缩短为研究非肌肉收缩提供了一个有用的模型，因为它是线性的、缓慢的和重复的。锥体细胞含有与收缩轴平行的细丝(肌动蛋白)和粗丝(肌球蛋白样)。本研究考察了锥体细丝的极性和伴随着光诱导收缩的细丝分布的变化，试图阐明锥体收缩过程的结构基础。锥体的近半部分固定在其外核层的细胞邻居上，而远半部分是自由的。因此，所有的缩短都发生在视锥的下半部分的颈状区域(肌样)，该区域延伸到神经视网膜和有色视网膜上皮之间的间隙。细丝贯穿视锥的整个长度，而粗丝主要出现在对光和暗适应的视锥的近端(轴突)区域。因此，粗丝主要集中在发生缩短的区域之外。肌球蛋白亚段1结合研究的观察结果表明，视锥的细丝被组织成两个相对的组。在视锥的远端半部分(包括肌突)，几乎所有的细丝都有指向近端的箭头。在轴突的较近端区域，许多细丝具有相反的极性，它们的箭头指向远端。在光适应(收缩)锥体的突触近端附近，两极相反的细丝出现的数量大致相等。因此，在锥体轴突中，似乎有两组重叠的肌动蛋白细丝，其相反的极性对应于肌肉肌节的两个肌动蛋白部分。在拉长的、适应黑暗的锥体中，粗丝分布在锥体的轴突区域。在光线下，粗丝向锥体的近端聚集。这些观察结果与锥体收缩的“滑动假说”是一致的，即粗大的肌球蛋白样细丝在近端轴突区域产生两组相反方向的肌动蛋白细丝滑动交错。因此，肌样细丝基本上会卷曲到轴突区域以产生缩短。再伸长的机制取决于微管，如配套文件中所讨论的。
The long slender retinal cones of fishes shorten in the light and elongate in the dark. Light-induced cone shortening provides a useful model for stuying nonmuscle contraction because it is linear, slow, and repetitive. Cone cells contain both thin (actin) and thick (myosinlike) filaments oriented parallel to the axis of contraction. This study examines the polarities of the cone's thin filaments and the changes in filament distribution which accompany light-induced contraction, in an attempt to elucidate the structural basis for the cone's contractile process. The proximal half of the cone is fixed to its cellular neighbors in the outer nuclear layer while the distal half is free. Thus, all shortening takes place in a necklike region (the myoid) in the distal half of the cone which extends into the space between the neural retina and the pigmented retinal epithelium. Thin filaments are found throughout the length of the cone, whereas thick filaments occur predominantly in the proximal (axon) regions of both light- and dark- adapted cones. Thus, thick filaments are primarily localized outside the region where shortening takes place. Observations from myosin subfragment-1 binding studies suggest that the cone's thin filaments are organized into two opposing sets. In the distal half of the cone (including the myoid), virtually all filaments have proximally directed arrowheads. In the more proximal regions of the axon, many thin filaments have opposite polarity, their arrowheads being distally directed. Near the synaptic proximal end of the light-adapted (contracted) cone, filaments of opposite polarities occur in approximately equal numbers. Thus, in the cone axon there appear to be two overlapping sets of actin filaments whose opposite polarities correspond to the two actin halves of a muscle sarcomere. In elongated, dark-adapted cones, thick filaments are localized throughout the axon region of the cone. In light, thick filaments accumulate towards the proximal end of the cone. These observations are consistent with a "sliding hypothesis" for cone contraction, in which thick myosinlike filaments produce sliding interdigitation of the two sets of oppositely directed actin filaments in the proximal axon region. Thus, the myoid thin filaments would be essentially reeled into the axon region to produce shortening. The mechanism of re-elongation depends on microtubules, as discussed in the companion paper.