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Isotropic Light-Sheet Microscopy and Automated Cell Lineage Analyses to Catalogue Caenorhabditis elegans Embryogenesis with Subcellular Resolution

Caenorhabditis elegans (C. elegans) stands out as the only organism in which the challenge of understanding the cellular origins of an entire nervous ...

University of Connecticut Health Center

WormGUIDES.org

Multinucleate cells are widespread in nature, yet the mechanism by which cells fuse their plasma membranes is poorly understood. To identify animal fusogens, we performed new screens for mutations that abolish cell fusion within tissues of C. elegans throughout development. We identified the gene eff-1, which is expressed as cells acquire fusion competence and encodes a novel integral membrane protein. EFF-1 sequence motifs suggest physicochemical actions that could cause adjacent bilayers to fuse. Mutations in the extracellular domain of EFF-1 completely block epithelial cell membrane fusion without affecting other perfusion events such as cell generation, patterning, differentiation, and adhesion. Thus, EFF-1 is a key component in the mechanism of cell fusion, a process essential to normal animal development.

The type I membrane protein EFF-1 is essential for developmental cell fusion.

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Regulatory and biophysical mechanisms of cell-cell fusion are largely unknown despite the fundamental requirement for fused cells in eukaryotic development. Only two cellular fusogens that are not of clear recent viral origin have been identified to date, both in nematodes. One of these, EFF-1, is necessary for most cell fusions in Caenorhabditis elegans. Unregulated EFF-1 expression causes lethality due to ectopic fusion between cells not developmentally programmed to fuse, highlighting the necessity of tight fusogen regulation for proper development. Identifying factors that regulate EFF-1 and its paralog AFF-1 could lead to discovery of molecular mechanisms that control cell fusion upstream of the action of a membrane fusogen. Bioinformatic analysis of the EFF-1A isoform's predicted cytoplasmic domain (endodomain) previously revealed two motifs that have high probabilities of interacting with 14-3-3 proteins when phosphorylated. Mutation of predicted phosphorylation sites within these motifs caused measurable loss of eff-1 gene function in cell fusion in vivo. Moreover, a human 14-3-3 isoform bound to EFF-1::GFP in vitro. We hypothesized that the two 14-3-3 proteins in C. elegans, PAR-5 and FTT-2, may regulate either localization or fusion-inducing activity of EFF-1.

Article	Year
The type I membrane protein EFF-1 is essential for developmental cell fusion. Developmental cell\| PubMed ID: 11879640	2002
Google 'EarthWorm'. Nature methods\| PubMed ID: 19718015	2009
The EFF-1A Cytoplasmic Domain Influences Hypodermal Cell Fusions in C. elegans But Is Not Dependent on 14-3-3 Proteins. PloS one\| PubMed ID: 26800457	2016

William Mohler

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