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The WASP-family verprolin-homologous (Wave) complex enhances actin-related protein 2/3 (Arp2/3)-mediated actin polymerization. Recently, we have identified a novel Wave complex–actin–Wnt/β-catenin–Sox9 pathway that regulates epidermal morphogenesis and proliferation. These findings highlight a mechanism by which actin polymerization impacts crucial signaling events in vivo. [ABSTRACT FROM AUTHOR]

The Arp2/3 complex, which nucleates actin filaments, comprises a stable assembly of seven-protein subunits including two actin-related proteins (Arp2 and Arp3). Previous work showed that Arp2/3 binds to the sides of actin filaments and is concentrated at the leading edges of motile cells. In the present study, we show that the Arp2/3 complex is critical for cytokinesis during early embryonic development in porcine parthenotes. The Arp2/3 complex is concentrated at the cortex of each cell at the 1-, 2-, and 4-cell stages, and at the periphery at the morula stage. The amount of Arp2/3 significantly decreased at the blastocyst stage in parthenogenetically activated porcine embryos. Inhibition of the Arp2/3 complex in the pig embryos by the Arp2/3-specific inhibitor CK666 resulted in abnormal cell division, a decrease in developmental rate and total cell numbers, and an increase in the ratio of trophectoderm cell number to inner cell mass number in blastocyst-stage embryos. In addition, 4-cell stage embryos subjected to CK666 treatment exhibited significantly decreased expression of ZGA genes (Pou5f1, Sox2, and Nanog), suggesting that the Arp2/3 complex plays an important role in early porcine embryo development. Thus, our data demonstrate that the Arp2/3 complex is required for early embryonic development in pigs and appears to regulate the expression of pluripotency genes. [ABSTRACT FROM AUTHOR]

Crustacean muscle fibers exhibit a high level of plasticity in various growth and developmental stages and understanding its mechanism is one of the important factors to improve the commercial value of the decapod products including shrimp, lobsters, and crabs. In the present study, four cDNAs encoding actins (PotActinSK1, PotActinSK2, PotActinHT, and PotActinCT) were identified from the swimming crab (Portunus trituberculatus) using a PCR-based cloning strategy. Although the four cDNA encoding actins exhibit similarities in size and deduced amino acid sequences, their tissue expression profiles differ significantly from one another. Phylogenetic analysis revealed that muscular and cytoplasmic actins have been diverged before vertebrates were evolved and cardiac and skeletal muscular actins were branched out after the vertebrates were evolved. Based on the phylogenetic analysis and expression patterns, PotActinSK1 and SK2 belong to the slow-type skeletal muscle actins and the fast-type skeletal muscle actin has not been identified. PotActinHT showed the highest sequence similarity to Ha-ActinHT fromH. americanusand appeared to be an ortholog of heart muscle actins in decapod crustaceans. PotActinCT exhibited the highest sequence similarity to the cytoplasmic actin ofL. vannameiActinT1. End-point RT-PCR results showed that PotActinSK1 and PotActinSK2 were strongly expressed in skeletal muscular tissues including chela propodus muscle, chela merus muscle, leg muscle, thoracic muscle, and there was no significant difference in the expression ratio between the two genes of those four tissues. PotActinCT was ubiquitously expressed in all the tissues, whereas PotActinHT was exclusively expressed in the heart. Interestingly, a considerable level of PotActinCT was expressed in the heart, which is similar to those of PotActinHT. The transcriptional response to 20-hydroxyecdysone (20E) injection was different in each PotActin suggesting that effects of muscle plasticity by 20E may differ in each tissue of decapod crustaceans. [ABSTRACT FROM AUTHOR]

Stereocilia are actin protrusions with remarkably well-defined lengths and organization. A flurry of recent papers has reported multiple myosin motor proteins involved in regulating stereocilia structures by transporting actin-regulatory cargo to the tips of stereocilia. In our recent paper, we show that two paralogous class 3 myosins -- Myo3a and Myo3b -- both transport the actinregulatory protein Espin 1 (Esp1) to stereocilia and filopodia tips in a remarkably similar, albeit non-identical fashion. Here we present experimental and computational data that suggests that subtle differences between these two proteins' biophysical and biochemical properties can help us understand how these myosin species target and regulate the lengths of actin protrusions. [ABSTRACT FROM AUTHOR]

It has been suggested that chromatin is organized into the stable structures that provide fundamental units of chromosome architecture in interphase mammalian cells. The stable structures of chromatin can be visualized as replication foci when replicating DNA is labeled with thymidine analogs. Previously, we showed that the chromosome territory expanded after BAF53 knockdown. In this study, we found that BAF53 is required for the formation of replication foci. DNA replication was not impaired in BAF53 knockdown cells, suggesting that the decrease in the number of replication foci is due to disintegration of replication foci, but not suppression of DNA replication. The attractive forces that maintain structural integrity of replication foci could be disrupted by BAF53 knockdown, and it may be responsible, at least in part, for the expansion of chromosome territories after BAF53 knockdown. [ABSTRACT FROM PUBLISHER]

Human respiratory syncytial virus (RSV) is the leading viral cause of severe lower respiratory disease in young children worldwide. As part of a genome-wide siRNA screen, we recently discovered that actin-related protein 2 (ARP2) is a host factor in the RSV replication cycle. ARP2 is a major constituent of the ARP2/3 complex, which catalyzes actin polymerization involved in cell morphology and motility. In the course of investigating this finding, we also found that RSV infection of human lung epithelial A459 cells induced filopodia formation and stimulated cell motility. The increase in filopodia formation was due, at least in part, to the expression of the RSV fusion F protein. Filopodia formation and increased cell motility appeared to shuttle RSV particles to nearby uninfected cells, facilitating virus cell-to-cell spread. ARP2 depletion did not reduce RSV entry or gene expression early in infection, but reduced subsequent virus production, filopodia formation, cell motility, and viral spread. Thus, the RSV F protein, ARP2-mediated actin nucleation, filopodia formation, and cell mobility all contribute to previously unrecognized mechanisms for RSV cell-to-cell spread that may promote RSV pathogenesis. [ABSTRACT FROM PUBLISHER]