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Buzz Baum

Publications and source records attributed to Buzz Baum.

15 recordsLinked to original sources
PubMed2006

Prostate-derived sterile 20-like kinase 1-alpha induces apoptosis. JNK- and caspase-dependent nuclear localization is a requirement for membrane blebbing.

We have demonstrated previously that full-length prostate-derived sterile 20-like kinase 1-alpha (PSK1-alpha) binds to microtubules via its C terminus and regulates their organization and stability independently of its catalytic activity. Here we have shown that apoptotic and microtubule-disrupting agents promote catalytic activation, C-terminal cleavage, and nuclear translocation of endogenous phosphoserine 181 PSK1-alpha and activated N-terminal PSK1-alpha-induced apoptosis. PSK1-alpha, unlike its novel isoform PSK1-beta, stimulated the c-Jun N-terminal kinase (JNK) pathway, and the nuclear localization of PSK1-alpha and its induction of cell contraction, membrane blebbing, and apoptotic body formation were dependent on JNK activity. PSK1-alpha was also a caspase substrate, and the broad spectrum caspase inhibitor benzyloxycarbonyl-VAD-fluoromethyl ketone or mutation of a putative caspase recognition motif ((916)DPGD(919)) blocked nuclear localization of PSK1-alpha and its induction of membrane blebs. Additional inhibition of caspase 9 was needed to prevent cell contraction. PSK1-alpha is therefore a bifunctional kinase that associates with microtubules, and JNK- and caspase-mediated removal of its C-terminal microtubule-binding domain permits nuclear translocation of the N-terminal region of PSK1-alpha and its induction of apoptosis.

Active Transport, Cell Nucleus↗
PubMed2006

Left-right asymmetry: actin-myosin through the looking glass.

Despite being bilaterally symmetric, most Metazoa exhibit clear, genetically determined left-right differences. In several animals, microtubule-based structures are thought to be the source of chiral information used to establish handedness. Now, two new studies in Drosophila identify a role for unconventional myosin motors in this process.

Actins↗
PubMed2006

FLIGHT: database and tools for the integration and cross-correlation of large-scale RNAi phenotypic datasets.

FLIGHT (www.flight.licr.org) is a new database designed to help researchers browse and cross-correlate data from large-scale RNAi studies. To date, the majority of these functional genomic screens have been carried out using Drosophila cell lines. These RNAi screens follow 100 years of classical Drosophila genetics, but have already revealed their potential by ascribing an impressive number of functions to known and novel genes. This has in turn given rise to a pressing need for tools to simplify the analysis of the large amount of phenotypic information generated. FLIGHT aims to do this by providing users with a gene-centric view of screen results and by making it possible to cluster phenotypic data to identify genes with related functions. Additionally, FLIGHT provides microarray expression data for many of the Drosophila cell lines commonly used in RNAi screens. This, together with information about cell lines, protocols and dsRNA primer sequences, is intended to help researchers design their own cell-based screens. Finally, although the current focus of FLIGHT is Drosophila, the database has been designed to facilitate the comparison of functional data across species and to help researchers working with other systems navigate their way through the fly genome.

Animals↗
PubMed2006

Minimizing the risk of reporting false positives in large-scale RNAi screens.

Large-scale RNA interference (RNAi)-based analyses, very much as other 'omic' approaches, have inherent rates of false positives and negatives. The variability in the standards of care applied to validate results from these studies, if left unchecked, could eventually begin to undermine the credibility of RNAi as a powerful functional approach. This Commentary is an invitation to an open discussion started among various users of RNAi to set forth accepted standards that would insure the quality and accuracy of information in the large datasets coming out of genome-scale screens.

Databases, Genetic↗
PubMed2006

Regulation of apicomplexan actin-based motility.

Apicomplexan parasites are an ancient group of protozoan parasites that includes several significant pathogens of humans and animals. To target and invade host cells they use a unique form of actin-based motility, called gliding motility. At the centre of the molecular motor that underlies this unique mode of locomotion are short, highly dynamic actin filaments. Recent molecular work, along with the availability of completed genomes for several Apicomplexa, has highlighted unique features of parasite actin and its regulation - features that might provide new ways to block motility and, consequently, prevent infection and disease.

Actins↗
PubMed2005

Actin nucleation: spire - actin nucleator in a class of its own.

The rate limiting step for actin filament polymerisation is nucleation, and two types of nucleator have been described: the Arp2/3 complex and the formins. A recent study has now identified in Spire a third class of actin nucleator. The four short WH2 repeats within Spire bind four consecutive actin monomers to form a novel single strand nucleus for 'barbed end' actin filament elongation.

Actins↗
PubMed2004

RNAi in a postmodern, postgenomic era.

As dsRNA-mediated interference (RNAi) libraries become more widely available, genome-wide loss of function experiments in cell culture are likely to become a routine laboratory tool. RNAi screens can then be conducted to test gene functions in different assays in a variety of cell types and across species. In comparing these large phenotypic data sets, researchers will gain a new perspective, enabling them to see each gene as part of a fluid network that is remodelled in response to changes in environmental and developmental context, and with the passage of evolutionary time.

Gene Library↗
PubMed2004

Animal development: crowd control.

To shape a developing animal, individual cell movements must be coordinated over long distances. Two recent studies help show how this is achieved during convergence and extension of the Drosophila germ-band, where polarity within the plane of the embryonic epithelium biases junction remodeling to polarize cell intercalation.

Adherens Junctions↗
PubMed2004

Myosin II-dependent cortical movement is required for centrosome separation and positioning during mitotic spindle assembly.

The role of myosin II in mitosis is generally thought to be restricted to cytokinesis. We present surprising new evidence that cortical myosin II is also required for spindle assembly in cells. Drug- or RNAi-mediated disruption of myosin II in cells interferes with normal spindle assembly and positioning. Time-lapse movies reveal that these treatments block the separation and positioning of duplicated centrosomes after nuclear envelope breakdown (NEBD), thereby preventing the migration of the microtubule asters to opposite sides of chromosomes. Immobilization of cortical movement with tetravalent lectins produces similar spindle defects to myosin II disruption and suggests that myosin II activity is required within the cortex. Latex beads bound to the cell surface move in a myosin II-dependent manner in the direction of the separating asters. We propose that after NEBD, completion of centrosome separation and positioning around chromosomes depends on astral microtubule connections to a moving cell cortex.

Actins↗
PubMed2004

Cascade pathway of filopodia formation downstream of SCAR.

The protrusion of two distinct actin-containing organelles, lamellipodia and filopodia, is thought to be regulated by two parallel pathways: from Rac1 through Scar/WAVEs to lamellipodia, and from Cdc42 through N-WASP to filopodia. We tested this hypothesis in Drosophila, which contains a single gene for each WASP subfamilies, SCAR and WASp. We performed targeted depletion of SCAR or WASp by dsRNA-mediated interference in two Drosophila cultured cell lines expressing lamellipodial and filopodial protrusion. Knockdown was verified by laser capture microdissection and RT-PCR, as well as western blotting. Morphometrical, kinetic and electron microscopy analyses of the SCAR-depleted phenotype in both cell types revealed strong inhibition of lamellipodial formation and cell spreading, as expected. More importantly, filopodia formation was also strongly inhibited, which is not consistent with the parallel pathway hypothesis. By contrast, depletion of WASp did not produce any significant phenotype, except for a slight inhibition of spreading, showing that both lamellipodia and filopodia in Drosophila cells are regulated predominantly by SCAR. We propose a new, cascade pathway model of filopodia regulation in which SCAR signals to lamellipodia and then filopodia arise from lamellipodia in response to additional signal(s).

Animals↗
PubMed2003

Abi, Sra1, and Kette control the stability and localization of SCAR/WAVE to regulate the formation of actin-based protrusions.

BACKGROUND: In animal cells, GTPase signaling pathways are thought to generate cellular protrusions by modulating the activity of downstream actin-regulatory proteins. Although the molecular events linking activation of a GTPase to the formation of an actin-based process with a characteristic morphology are incompletely understood, Rac-GTP is thought to promote the activation of SCAR/WAVE, whereas Cdc42 is thought to initiate the formation of filopodia through WASP. SCAR and WASP then activate the Arp2/3 complex to nucleate the formation of new actin filaments, which through polymerization exert a protrusive force on the membrane. RESULTS: Using RNAi to screen for genes regulating cell form in an adherent Drosophila cell line, we identified a set of genes, including Abi/E3B1, that are absolutely required for the formation of dynamic protrusions. These genes delineate a pathway from Cdc42 and Rac to SCAR and the Arp2/3 complex. Efforts to place Abi in this signaling hierarchy revealed that Abi and two components of a recently identified SCAR complex, Sra1 (p140/PIR121/CYFIP) and Kette (Nap1/Hem), protect SCAR from proteasome-mediated degradation and are critical for SCAR localization and for the generation of Arp2/3-dependent protrusions. CONCLUSIONS: In Drosophila cells, SCAR is regulated by Abi, Kette, and Sra1, components of a conserved regulatory SCAR complex. By controlling the stability, localization, and function of SCAR, these proteins may help to ensure that Arp2/3 activation and the generation of actin-based protrusions remain strictly dependant on local GTPase signaling.

Actins↗
PubMed2002

A Drosophila homolog of cyclase-associated proteins collaborates with the Abl tyrosine kinase to control midline axon pathfinding.

We demonstrate that Drosophila capulet (capt), a homolog of the adenylyl cyclase-associated protein that binds and regulates actin in yeast, associates with Abl in Drosophila cells, suggesting a functional relationship in vivo. We find a robust and specific genetic interaction between capt and Abl at the midline choice point where the growth cone repellent Slit functions to restrict axon crossing. Genetic interactions between capt and slit support a model where Capt and Abl collaborate as part of the repellent response. Further support for this model is provided by genetic interactions that both capt and Abl display with multiple members of the Roundabout receptor family. These studies identify Capulet as part of an emerging pathway linking guidance signals to regulation of cytoskeletal dynamics and suggest that the Abl pathway mediates signals downstream of multiple Roundabout receptors.

Animals↗
PubMed2002

Winging it--actin on the fly.

How actin dynamics might be regulated to generate specific cellular structures during development remains something of a mystery. New insights may be gained from the recent identification of a conserved cofilin phosphatase, Slingshot, which modulates actin dynamics to help control Drosophila wing hair morphogenesis.

Actins↗