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

• Here, we investigated how tropomyosin stabilizes actin filaments and how this function is influenced by muscle contraction in Caenorhabditis elegans body wall muscle [6].
• RNA interference of Ce-kettin caused weak disorganization of the actin filaments in body wall muscle [7].
• Although the model refers primarily to the locomotion of nematode sperm, it has important implications for the mechanics of actin-based cell motility [8].
• It is hypothesized that actin plays a role in the shaping of the cell and in the arrangement of its organelles during nematode spermiogenesis, when MSP is present, in an inactive state, in the fibrous bodies [9].
• In Caenorhabditis elegans and Ascaris suum, previous studies have reported that sperm motility does not involve actin, but, instead, requires a specific cytoskeletal protein, namely major-sperm-protein (MSP) [9].

Anatomical context of actin

• Given these advantages, it has been possible to use C. elegans to investigate the different ways in which the actin cytoskeleton drives the cellular rearrangements underlying morphogenesis, through regulated polymerization or actomyosin contraction [2].
• TM4SF10 colocalized with ZO1 and p120ctn in undifferentiated confluent podocytes and also colocalized with the tips of actin filaments at cell contacts [10].
• Tropomyosin shows a distinct pattern in spermatids, but is located in the MSP and actin-containing cap in spermatozoa [9].
• We have studied the localization of actin and MSP in spermatids and spermatozoa of Graphidium strigosum (Dujardin, 1845), a species which has elongate male germ cells in which organelles are easily identified [11].
• Immunocytochemical observations reveal that actin and MSP have an identical localization in precise areas of the male germ cells [11].

Other interactions of actin

• These results suggest that muscle contraction has only minor influence on the tropomyosin's protective role against ADF/cofilin and AIP1, and that the two functions of tropomyosin in actin stability and muscle contraction are independent of each other [6].
• Moreover, nematode sperm lack detectable molecular motors or the battery of actin-binding proteins that characterize actin-based motility [8].
• Sperm of the nematode, Ascaris suum, are amoeboid cells that do not require actin or myosin to crawl over solid substrata [12].
• The very thin filaments were visualized in gelsolin-treated actin filament-free fibres [13].
• 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].

Analytical, diagnostic and therapeutic context of actin

• 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 [15].
• The FBs contain actin as shown by immunofluorescence using a monoclonal anti-actin antibody and by affinity cytochemistry using fluorescent phalloidin [16].

References