Biochemical Society Annual Symposium No. 77 Networking in the endoplasmic reticulum

Abstract The network of the ER (endoplasmic reticulum) is set up by cytoskeletal control of the movement and remodelling of polygonal rings of tubules, bundles of tubules and cisternal regions. We have developed a new image analysis tool, persistency mapping, to understand the framework upon which the plant ER remodels. With this new tool, we have explored the network nodes, called anchor/growth sites, that may anchor the network by attachment to the plasma membrane. We have determined how the polygonal ring structure depends on myosin XI-K for 'opening' and 'closing'. With latrunculin B treatment, we have investigated the involvement of actin in the elongation and persistency of the tubules. We also show how the cytoskeleton is involved in directional diffusion within the membrane. This observation may lead to an answer to the question of what function this network structure serves in the cell. We propose that the ER acts as a trafficking network, delivering lipid, protein, calcium and signalling molecules to different regions of the cell. It does so by directional reduced dimensional diffusion. The ER network of tubules restricts the dimensionality of diffusion to near one-dimensional, whereas the cisternae reduce it to near two-dimensional. The cytoskeleton does not drive the diffusion, but participates by providing directionality to the diffusion

ER network dynamics are differentially controlled by myosins XI-K, XI-C, XI-E, XI-I, XI-1, and XI-2

This document is protected by copyright and was first published by Frontiers. All rights reserved. It is reproduced with permission.The endoplasmic reticulum (ER) of higher plants is a complex network of tubules and cisternae. Some of the tubules and cisternae are relatively persistent, while others are dynamically moving and remodeling through growth and shrinkage, cycles of tubule elongation and retraction, and cisternal expansion and diminution. Previous work showed that transient expression in tobacco leaves of the motor-less, truncated tail of myosin XI-K increases the relative area of both persistent cisternae and tubules in the ER. Likewise, transient expression of XI-K tail diminishes the movement of organelles such as Golgi and peroxisomes. To examine whether other class XI myosins are involved in the remodeling and movement of the ER, other myosin XIs implicated in organelle movement, XI-1 (MYA1),XI-2 (MYA2), XI-C, XI-E, XI-I, and one not, XI-A, were expressed as motor-less tail constructs and their effect on ER persistent structures determined. Here, we indicate a differential effect on ER dynamics whereby certain class XI myosins may have more influence over controlling cisternalization rather than tubulation.Biotechnology & Biological Sciences Research Council (BBSRC)Biology department at Texas A and M Universit