High impact information on actin

• In hair cells of the inner ear, evidence suggests that an extracellular tip link pulls on a channel, which attached intracellularly to actin via a tension-regulating myosin 1beta [1].
• Recent insights from this system have determined the involvement in morphogenesis of key proteins, including the actin-regulating WASP and Ena proteins, potential guidance molecules such as the Eph and Robo receptors, and the cell-cell signaling proteins of the Wnt pathway [2].
• Sperm from nematodes use a major sperm protein (MSP) cytoskeleton in place of an actin cytoskeleton to drive their ameboid locomotion [3].
• They lack an axoneme or the actin and myosins of other types of motile cells, but their pseudopods contain abundant major sperm protein (MSP), a family of 14-kD polypeptides found exclusively in male gametes [4].
• ERM proteins regulate cell morphology and plasma membrane dynamics by reversibly anchoring actin filaments to integral plasma membrane proteins [5].

Biological context of actin

• RNA interference of Ce-kettin caused weak disorganization of the actin filaments in body wall muscle [6].
• Although the model refers primarily to the locomotion of nematode sperm, it has important implications for the mechanics of actin-based cell motility [7].
• The FOZI-1 protein displays a highly unusual domain architecture, that combines two functionally essential C2H2 zinc-finger domains, which are probably involved in transcriptional regulation, with a formin homology 2 (FH2) domain, normally found only in cytosolic regulators of the actin cytoskeleton [8].
• Here, we performed a detailed characterization of the pha-2 phenotype using cell-type-specific reporters, physical manipulation of the nuclei in pharyngeal muscle cells using "optical tweezers", electron microscopy, staining of the actin cytoskeleton as well as phenotypic rescue and ectopic expression experiments [9].
• Thus, filament polarity and on-filament ATP hydrolysis, although essential for actin-based motility, appear to be unnecessary for membrane protrusions by MSP [10].

Anatomical context of actin

• However, rather than employing an actin cytoskeleton to generate locomotion, nematode sperm use the major sperm protein (MSP) [7].
• The major sperm protein (MSP) is the central cytoskeletal element required for actin-independent motility of nematode spermatozoa [11].
• We also demonstrate that an interaction between MIG-10 and UNC-34, a protein that promotes actin-filament extension, is important in the response to guidance cues and that MIG-10 colocalizes with actin in cultured cells, where it can induce the formation of lamellipodia [12].
• In nematode sperm cell motility, major sperm protein (MSP) filament assembly results in dynamic membrane protrusions in a manner that closely resembles actin-based motility in other eukaryotic cells [10].
• The reconstitution of filopodial extension shows that, like the actin cytoskeleton, MSP filaments can adopt two architectures, bundles and meshworks, each capable of pushing against membranes to generate protrusion [13].

Other interactions of actin

• Moreover, nematode sperm lack detectable molecular motors or the battery of actin-binding proteins that characterize actin-based motility [7].
• The increased synthesis of forms of myosin, actin and troponin in the nematode living in the rapid-responder SWR host may relate to the attempted reorganisation or repair of the cytoskeleton and/or muscle layer in the host immune initiated, increased mucus production and smooth muscle activity within intestinal environment [14].
• Sperm of the nematode, Ascaris suum, are amoeboid cells that do not require actin or myosin to crawl over solid substrata [15].

Analytical, diagnostic and therapeutic context of actin

• The FBs contain actin as shown by immunofluorescence using a monoclonal anti-actin antibody and by affinity cytochemistry using fluorescent phalloidin [16].

References