Three‐dimensional organization of endoplasmic reticulum in the ventral photoreceptors of Limulus

Abstract

Living Limulus ventral photoreceptor cells were injected with long chain lipophilic carbocyanine fluorescent dyes to label the endoplasmic reticulum (ER). The purpose of this study was to examine the continuity, dynamic changes, and structure of the ER in the living cell, using laser scanning confocal microscopy and three-dimensional image reconstruction. In this highly polarized neuron, three lines of evidence indicate that the ER is a continuous network extending throughout both lobes of the cell. First, injection of DiO or DiI results in the labeling of ER throughout both lobes of the cell. Second, three-dimensional image reconstruction of the optical sections reveals a dispersed membrane meshwork which may be the structure that serves to interconnect the ER in the two lobes. Third, in cells fixed before dye injection, the pattern of labeling was similar to that in living cells, indicating that vesicle transport was not responsible for the spread of dye throughout the cell. The overall organization of the ER in the photoreceptor cell is relatively stable; however, the fine structure changes over time. This dynamic process appears to represent continual reorganization of the intracellular membranes in the cell. Three morphological types of ER were observed. The ER of the light-sensitive lobe, identified by coinjection of rhodamine-phalloidin to label the microvillar actin, is characterized by a concentration of stratiform membranes interconnected by thin tubular cross-bridges. The perinuclear ER is characterized by a tangle of convoluted tubules sometimes terminating in bulbous structures. Finally, there is a fine tubular reticulum dispersed throughout the cell.

Dynamic and reversible restructuring of the ER induced by PDMP in cultured cells

“…Carbocyanine dyes that contain saturated alkyl chains, like DiIC 18 (3) and DiIC 16 (3), are known to partition into liquidordered domains of the plasma membrane in living cells (Hao et al, 2001;Pierini et al, 1996;Thomas et al, 1994). When microinjected into different kinds of cells (Feng et al, 1994;Mehlmann et al, 1995;Terasaki and Jaffe, 1991;Terasaki et al, 1994) these dyes have been reported to stain the ER. Consistently, DiIC 16 (3) microinjected into induced HeLa cells, produced an ER staining pattern superimposable on that of GFP-b(5)tail (Fig.…”

Effects of Calcium and Cyclopiazonic Acid on the Photoresponse in the Limulus Ventral Photoreceptor

“…Bright illumination evokes a macroscopic photore sponse that consists of many temporarily and spa tially fused bumps (Dogde, Knight and Toyoda, 1968;Brown and Coles, 1979;Stieve, 1986 The electrical photoresponse is accompanied by a rise in the concentration of free calcium ions in the cytoplasm (Brown, Brown and Pinto, 1977;Maaz and Stieve, 1980;Levy and Fein, 1985). In the ventral photoreceptor the endoplasmic reticu lum forms an extensive network in which calcium is stored and from which it is released after illumi nation (Payne, Walz, Levy and Fein, 1988;Feng, Carson, Morgan, Walz and Fein, 1994). In addition to release from internal stores calcium influx from the extracellular space contributes to the transient augmentation of the cytosolic free calcium concen tration (Stommel, Dorlöchter, Rüsing and Stieve, 1996).…”

Continuous network of endoplasmic reticulum in cerebellar Purkinje neurons.

“…Study ofeggs fixed before injection made it clear that the DiI spread through continuous membranes and that the cortical ER network, the interior membrane lamellae, and the nuclear envelope are continuous. In another study, DiI was injected into fixed, isolated Limulus ventral photoreceptor cells, where it was concluded that the ER is continuous between the phototransducing lobe and the lobe containing the nucleus (9).…”