Evolution of the eukaryotic dynactin complex, the activator of cytoplasmic dynein

Björn Hammesfahr,Martin Kollmar

doi:10.1186/1471-2148-12-95

Abstract

BackgroundDynactin is a large multisubunit protein complex that enhances the processivity of cytoplasmic dynein and acts as an adapter between dynein and the cargo. It is composed of eleven different polypeptides of which eight are unique to this complex, namely dynactin1 (p150Glued), dynactin2 (p50 or dynamitin), dynactin3 (p24), dynactin4 (p62), dynactin5 (p25), dynactin6 (p27), and the actin-related proteins Arp1 and Arp10 (Arp11).ResultsTo reveal the evolution of dynactin across the eukaryotic tree the presence or absence of all dynactin subunits was determined in most of the available eukaryotic genome assemblies. Altogether, 3061 dynactin sequences from 478 organisms have been annotated. Phylogenetic trees of the various subunit sequences were used to reveal sub-family relationships and to reconstruct gene duplication events. Especially in the metazoan lineage, several of the dynactin subunits were duplicated independently in different branches. The largest subunit repertoire is found in vertebrates. Dynactin diversity in vertebrates is further increased by alternative splicing of several subunits. The most prominent example is the dynactin1 gene, which may code for up to 36 different isoforms due to three different transcription start sites and four exons that are spliced as differentially included exons.ConclusionsThe dynactin complex is a very ancient complex that most likely included all subunits in the last common ancestor of extant eukaryotes. The absence of dynactin in certain species coincides with that of the cytoplasmic dynein heavy chain: Organisms that do not encode cytoplasmic dynein like plants and diplomonads also do not encode the unique dynactin subunits. The conserved core of dynactin consists of dynactin1, dynactin2, dynactin4, dynactin5, Arp1, and the heterodimeric actin capping protein. The evolution of the remaining subunits dynactin3, dynactin6, and Arp10 is characterized by many branch- and species-specific gene loss events.

Highlights

Dynactin is a large multisubunit protein complex that enhances the processivity of cytoplasmic dynein and acts as an adapter between dynein and the cargo
Dynactin protein sequences are not as strongly conserved as for example tubulins, and three of the dynactin subunits are relatively short complicating their identification if they were spread on several exons
The dynactin subunits might have been duplicated in single species or certain branches, like the Drosophila dynactin1 gene [48]

Summary

Introduction

Dynactin is a large multisubunit protein complex that enhances the processivity of cytoplasmic dynein and acts as an adapter between dynein and the cargo. The dynein-dynactin complex plays an important role during mitosis [9,10] and is necessary for synapse stabilization [11]. It is involved in nuclear migration, and during cell division in mitotic spindle positioning [12,13,14] and organization of spindle microtubule arrays [15]. Most of dynactins functions are in conjunction with cytoplasmic dynein it binds to and modulates kinesin-2 [16,17] and kinesin-5 [18].

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