Biomedical subjects

Nicole S Bryce

Publications and source records attributed to Nicole S Bryce.

4 recordsLinked to original sources

PubMed2005

Cortactin promotes cell motility by enhancing lamellipodial persistence.

BACKGROUND: Lamellipodial protrusion, which is the first step in cell movement, is driven by actin assembly and requires activity of the Arp2/3 actin-nucleating complex. However, it is unclear how actin assembly is dynamically regulated to support effective cell migration. RESULTS: Cells deficient in cortactin have impaired cell migration and invasion. Kymography analyses of live-cell imaging studies demonstrate that cortactin-knockdown cells have a selective defect in the persistence of lamellipodial protrusions. The motility and protrusion defects are fully rescued by cortactin molecules, provided both the Arp2/3 complex and F-actin binding sites are intact. Consistent with this requirement for simultaneous contacts with Arp2/3 and F-actin, cortactin is recruited by Arp2/3 complex to lamellipodia and binds with a higher affinity to ATP/ADP-Pi-F-actin than to ADP-F-actin. In situ labeling of lamellipodia revealed that the relative levels of free barbed ends of actin filaments are reduced by over 30% in the cortactin-knockdown cells; however, there is no change in Arp2/3-complex localization to lamellipodia. Cortactin-knockdown cells also have a selective defect in the assembly of new adhesions in protrusions, as assessed by analysis of GFP-paxillin dynamics in living cells. CONCLUSIONS: Cortactin enhances lamellipodial persistence, at least in part through regulation of Arp2/3 complex. The presence of cortactin also enhances the rate of new adhesion formation in lamellipodia. In vivo, these functions may be important during directed cell motility.

Actin-Related Protein 2↗

PubMed2005

Specific features of neuronal size and shape are regulated by tropomyosin isoforms.

Spatially distinct populations of microfilaments, characterized by different tropomyosin (Tm) isoforms, are present within a neuron. To investigate the impact of altered tropomyosin isoform expression on neuronal morphogenesis, embryonic cortical neurons from transgenic mice expressing the isoforms Tm3 and Tm5NM1, under the control of the beta-actin promoter, were cultured in vitro. Exogenously expressed Tm isoforms sorted to different subcellular compartments with Tm5NM1 enriched in filopodia and growth cones, whereas the Tm3 was more broadly localized. The Tm5NM1 neurons displayed significantly enlarged growth cones accompanied by an increase in the number of dendrites and axonal branching. In contrast, Tm3 neurons displayed inhibition of neurite outgrowth. Recruitment of Tm5a and myosin IIB was observed in the peripheral region of a significant number of Tm5NM1 growth cones. We propose that enrichment of myosin IIB increases filament stability, leading to the enlarged growth cones. Our observations support a role for different tropomyosin isoforms in regulating interactions with myosin and thereby regulating morphology in specific intracellular compartments.

Actin Cytoskeleton↗

PubMed2005

Tissue-specific tropomyosin isoform composition.

Four distinct genes encode tropomyosin (Tm) proteins, integral components of the actin microfilament system. In non-muscle cells, over 40 Tm isoforms are derived using alternative splicing. Distinct populations of actin filaments characterized by the composition of these Tm isoforms are found differentially sorted within cells (Gunning et al. 1998b). We hypothesized that these distinct intracellular compartments defined by the association of Tm isoforms may allow for independent regulation of microfilament function. Consequently, to understand the molecular mechanisms that give rise to these different microfilaments and their regulation, a cohort of fully characterized isoform-specific Tm antibodies was required. The characterization protocol initially involved testing the specificity of the antibodies on bacterially produced Tm proteins. We then confirmed that these Tm antibodies can be used to probe the expression and subcellular localization of different Tm isoforms by Western blot analysis, immunofluorescence staining of cells in culture, and immunohistochemistry of paraffin wax-embedded mouse tissues. These Tm antibodies, therefore, have the capacity to monitor specific actin filament populations in a range of experimental systems.

Actins↗

PubMed2003

Specification of actin filament function and molecular composition by tropomyosin isoforms.

The specific functions of greater than 40 vertebrate nonmuscle tropomyosins (Tms) are poorly understood. In this article we have tested the ability of two Tm isoforms, TmBr3 and the human homologue of Tm5 (hTM5(NM1)), to regulate actin filament function. We found that these Tms can differentially alter actin filament organization, cell size, and shape. hTm5(NM1) was able to recruit myosin II into stress fibers, which resulted in decreased lamellipodia and cellular migration. In contrast, TmBr3 transfection induced lamellipodial formation, increased cellular migration, and reduced stress fibers. Based on coimmunoprecipitation and colocalization studies, TmBr3 appeared to be associated with actin-depolymerizing factor/cofilin (ADF)-bound actin filaments. Additionally, the Tms can specifically regulate the incorporation of other Tms into actin filaments, suggesting that selective dimerization may also be involved in the control of actin filament organization. We conclude that Tm isoforms can be used to specify the functional properties and molecular composition of actin filaments and that spatial segregation of isoforms may lead to localized specialization of actin filament function.

Actins↗