Formation of photoreceptors in larval and adult goldfish
Formation of photoreceptors in larval and adult goldfish
复制标题
幼体和成体金鱼光感受器的形成
作者：
P. R. Johns
用形态计量学和胸苷放射自显影技术在光镜水平上研究了金鱼视网膜感光层的组织发生。在孵化时，感光细胞层分化不良。外核层中的细胞在孵化时处于有丝分裂后分化成视锥细胞。孵化后2 ~ 3天，外核层出现杆状细胞核，杆状细胞开始分化。视杆细胞和视杆细胞核在幼虫和幼鱼的视网膜上积累。有人提出，杆产生的外核层分裂祖细胞，可能是类似于脑室下细胞。视杆祖细胞似乎来源于内核层中的未分化细胞簇，其被称为神经源性簇。这些细胞中的一些明显地从内核层迁移穿过外丛状层到外核层，然后分裂产生杆。光感受器发育的个体发生顺序在幼虫和成人视网膜边缘的圆周生长区不断重演。新的视杆继续插入，但速度较慢，贯穿整个成人视网膜;这可以解释尽管伴随着眼睛生长的视网膜表面扩张，视杆的密度如何保持恒定。
Histogenesis of the photoreceptor layer in the retina of goldfish was studied morphometrically and with thymidine radioautography at the light microscopic level. At hatching, the photoreceptor layer is poorly differentiated. The cells in the outer nuclear layer that are postmitotic' at hatching differentiate into cones. Two to 3 days after hatching, rod nuclei appear in the outer nuclear layer , and rods begin to differentiate. Rods and rod nuclei accumulate across the retina during larval and juvenile life. It is proposed that rods are generated in the outer nuclear layer by dividing progenitor cells that may be analogous to subventricular cells. Rod progenitors appear to derive from clusters of undifferentiated cells in the inner nuclear layer, which are called neurogenic clusters. Some of these cells apparently migrate across the outer plexiform layer from the inner to the outer nuclear layer and then divide to produce rods. The ontogenetic sequence of photoreceptor development in the larval retina is recapitulated continuously in the circumferential growth zone at the margin of the juvenile and adult retina. New rods continue to be inserted, but at a slower rate, throughout the adult retina; this may explain how the density of rods is maintained constant despite the expansion of the retinal surface that accompanies growth of the eye.