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Fusion-pore expansion during syncytium formation is restricted by an actin network.

ABSTRACT: Cell-cell fusion in animal development and in pathophysiology involves expansion of nascent fusion pores formed by protein fusogens to yield an open lumen of cell-size diameter. Here we explored the enlargement of micron-scale pores in syncytium formation, which was initiated by a well-characterized fusogen baculovirus gp64. Radial expansion of a single or, more often, of multiple fusion pores proceeds without loss of membrane material in the tight contact zone. Pore growth requires cell metabolism and is accompanied by a local disassembly of the actin cortex under the pores. Effects of actin-modifying agents indicate that the actin cortex slows down pore expansion. We propose that the growth of the strongly bent fusion-pore rim is restricted by a dynamic resistance of the actin network and driven by membrane-bending proteins that are involved in the generation of highly curved intracellular membrane compartments.

SUBMITTER: Chen A

PROVIDER: S-EPMC3552434 | biostudies-literature | 2008 Nov

REPOSITORIES: biostudies-literature

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Fusion-pore expansion during syncytium formation is restricted by an actin network.

Chen Andrew A Leikina Eugenia E Melikov Kamran K Podbilewicz Benjamin B Kozlov Michael M MM Chernomordik Leonid V LV

Journal of cell science 20081101 Pt 21

Cell-cell fusion in animal development and in pathophysiology involves expansion of nascent fusion pores formed by protein fusogens to yield an open lumen of cell-size diameter. Here we explored the enlargement of micron-scale pores in syncytium formation, which was initiated by a well-characterized fusogen baculovirus gp64. Radial expansion of a single or, more often, of multiple fusion pores proceeds without loss of membrane material in the tight contact zone. Pore growth requires cell metabol ...[more]

PMID: 18946025

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Project description:It is often assumed that upon fusion of the secretory granule membrane with the plasma membrane, lumenal contents are rapidly discharged and dispersed into the extracellular medium. Although this is the case for low-molecular-weight neurotransmitters and some proteins, there are numerous examples of the dispersal of a protein being delayed for many seconds after fusion. We have investigated the role of fusion-pore expansion in determining the contrasting discharge rates of fluorescent-tagged neuropeptide-Y (NPY) (within 200 ms) and tissue plasminogen activator (tPA) (over many seconds) in adrenal chromaffin cells. The endogenous proteins are expressed in separate chromaffin cell subpopulations. Fusion pore expansion was measured by two independent methods, orientation of a fluorescent probe within the plasma membrane using polarized total internal reflection fluorescence microscopy and amperometry of released catecholamine. Together, they probe the continuum of the fusion-pore duration, from milliseconds to many seconds after fusion. Polarized total internal reflection fluorescence microscopy revealed that 71% of the fusion events of tPA-cer-containing granules maintained curvature for >10 s, with approximately half of the structures likely connected to the plasma membrane by a short narrow neck. Such events were not commonly observed upon fusion of NPY-cer-containing granules. Amperometry revealed that the expression of tPA-green fluorescent protein (GFP) prolonged the duration of the prespike foot ?2.5-fold compared to NPY-GFP-expressing cells and nontransfected cells, indicating that expansion of the initial fusion pore in tPA granules was delayed. The t1/2 of the main catecholamine spike was also increased, consistent with a prolonged delay of fusion-pore expansion. tPA added extracellularly bound to the lumenal surface of fused granules. We propose that tPA within the granule lumen controls its own discharge. Its intrinsic biochemistry determines not only its extracellular action but also the characteristics of its presentation to the extracellular milieu.

Dataset Information

Fusion-pore expansion during syncytium formation is restricted by an actin network.

Publications

Fusion-pore expansion during syncytium formation is restricted by an actin network.

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