Biomedical subjects

Timothy M Gomez

Publications and source records attributed to Timothy M Gomez.

9 recordsLinked to original sources

PubMed2006

An antiangiogenic neurokinin-B/thromboxane A2 regulatory axis.

Establishment of angiogenic circuits that orchestrate blood vessel development and remodeling requires an exquisite balance between the activities of pro- and antiangiogenic factors. However, the logic that permits complex signal integration by vascular endothelium is poorly understood. We demonstrate that a "neuropeptide," neurokinin-B (NK-B), reversibly inhibits endothelial cell vascular network assembly and opposes angiogenesis in the chicken chorioallantoic membrane. Disruption of endogenous NK-B signaling promoted angiogenesis. Mechanistic analyses defined a multicomponent pathway in which NK-B signaling converges upon cellular processes essential for angiogenesis. NK-B-mediated ablation of Ca2+ oscillations and elevation of 3'-5' [corrected] cyclic adenosine monophosphate (cAMP) reduced cellular proliferation, migration, and vascular endothelial growth factor receptor expression and induced the antiangiogenic protein calreticulin. Whereas NK-B initiated certain responses, other activities required additional stimuli that increase cAMP. Although NK-B is a neurotransmitter/ neuromodulator and NK-B overexpression characterizes the pregnancy-associated disorder preeclampsia, NK-B had not been linked to vascular remodeling. These results establish a conserved mechanism in which NK-B instigates multiple activities that collectively oppose vascular remodeling.

1-Methyl-3-isobutylxanthine↗

PubMed2006

Focal adhesion kinase signaling at sites of integrin-mediated adhesion controls axon pathfinding.

Extracellular matrix (ECM) components regulate neurite outgrowth in tissue culture and in vivo. Live imaging of phosphotyrosine (PY) signals revealed that Xenopus laevis growth cones extending on permissive ECM substrata assemble adhesive point contacts containing enriched levels of tyrosine-phosphorylated proteins. Whereas focal adhesion kinase (FAK) signaling is dispensable for the assembly of focal adhesions in non-neuronal cells, FAK activity is required for the formation of growth cone point contacts. FAK-dependent point contacts promote rapid neurite outgrowth by stabilizing lamellipodial protrusions on permissive ECM substrata. Moreover, local FAK activity is required for ECM-dependent growth cone turning in vitro, suggesting that FAK may control axon pathfinding in vivo. Consistent with this possibility, proper growth and guidance of Rohon-Beard sensory neurons and spinal commissural interneurons requires FAK activity. These findings identify FAK as a key regulator of axon growth and guidance downstream of growth cone-ECM interactions.

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PubMed2006

Ca2+ influx through mechanosensitive channels inhibits neurite outgrowth in opposition to other influx pathways and release from intracellular stores.

Ca2+ signals are known to be important regulators of neurite outgrowth and steering. Here we show that inhibiting Ca2+ influx through stretch-activated channels using various compounds, including a highly specific peptide isolated from Grammostola spatulata spider venom (GsMTx4), strongly accelerates the rate of neurite extension on diverse substrata and within the intact spinal cord. Consistent with the presence of stretch-activated channels, we show that Ca2+ influx is triggered by hypotonic solutions, which can be partially blocked by GsMTx4. Finally, chelating local, but not global, Ca2+ signals prevents the acceleration that is normally produced by GsMTx4. Blocking Ca2+ influx through other channel types has little or opposite effects, but release from intracellular stores is required for maximal acceleration. Together, our data suggest that Ca2+ functions at distinct microdomains in growth cones, with influx through mechanosensitive channels acting to inhibit outgrowth in opposition to influx through other plasma membrane channels and release from stores.

Animals↗

PubMed2006

Rac1 and RhoA promote neurite outgrowth through formation and stabilization of growth cone point contacts.

Growth cone advance depends on coordinated membrane protrusion and adhesion to the extracellular matrix. Although many studies have addressed the mechanisms responsible for membrane protrusion, the assembly of integrin-dependent adhesion sites known as point contacts remains poorly understood in growth cones. We show balanced Rac1 activity controls both leading edge protrusion and point contact dynamics during neurite outgrowth. Immunocytochemistry and live imaging of paxillin-green fluorescent protein (GFP) showed that inhibiting Rac1 blocked point contact formation, whereas Rac1 overactivation produced small, unstable point contacts. Both inhibition and overactivation of Rac1 reduced the persistence of lamellar protrusions and neurite outgrowth. Inhibition of ROCK (Rho kinase), a RhoA effector, perturbed protrusion and point contact dynamics similar to Rac1 overactivation. Moreover, the repulsive guidance cue Semaphorin 3A, which signals through Rac1, destabilizes point contacts. Together, our data suggest that coordinated Rho GTPase activities regulate neurite outgrowth through point contact formation and stabilization of membrane protrusion.

Animals↗

PubMed2006

The molecular basis for calcium-dependent axon pathfinding.

Ca(2+) signals have profound and varied effects on growth cone motility and guidance. Modulation of Ca(2+) influx and release from stores by guidance cues shapes Ca(2+) signals, which determine the activation of downstream targets. Although the precise molecular mechanisms that underlie distinct Ca(2+)-mediated effects on growth cone behaviours remain unclear, recent studies have identified important players in both the regulation and targets of Ca(2+) signals in growth cones.

Animals↗

PubMed2005

Adjacent pioneer commissural interneuron growth cones switch from contact avoidance to axon fasciculation after midline crossing.

Commissural interneurons (CI) of the vertebrate spinal cord are guided ventrally toward the floor plate, but subsequently cross the midline and select a longitudinal fascicle at specific dorsal-ventral (D-V) positions. We examined at high resolution the detailed behaviors of individual pathfinding CI growth cones on the ipsilateral and contralateral sides of the spinal cord of living Xenopus embryos. We find that pre-crossing CI growth cones exhibit distinct pathfinding behaviors compared to post-crossing axons and that the behavioral switch occurs immediately upon crossing to the contralateral side. Groups of pioneer commissural axons typically extend simultaneously toward the ventral midline following discrete paths with separation between adjacent commissurals apparently maintained through contact inhibition. In contrast, shortly after crossing the midline, commissural axons turn longitudinally and begin to fasciculate with other crossed CIs. However, growth cones of crossed commissurals often select their final D-V longitudinal track through a series of rapid step-like dorsal adjustments that may be due to differential fasciculation with longitudinal axons. Together, our results suggest that guidance of commissural axons is controlled in part through interactions among CIs that switch rapidly from avoidance to fasciculation after midline crossing.

Animals↗

PubMed2005

Src-dependent tyrosine phosphorylation at the tips of growth cone filopodia promotes extension.

Extracellular cues guide axon outgrowth by activating intracellular signaling cascades that control the growth cone cytoskeleton. However, the spatial and temporal coordination of signaling intermediates remains essentially unknown. Live imaging of tyrosine phosphorylation in growth cones revealed dynamic phospho-tyrosine (PY) signals in filopodia that directly correlate with filopodial behavior. Local PY signals are generated at distal tips of filopodia during extension and are lost during retraction. Active Src family kinases localize to the tips of filopodia, and Src activity regulates both filopodial dynamics and local PY signaling. Positive guidance cues stimulate filopodial motility by locally increasing tyrosine phosphorylation in a cell division cycle 42 (Cdc42)-dependent manner. Locally reduced Src activity on one side of the growth cone generates an asymmetry in filopodial motility and PY signaling that promotes repulsive turning, suggesting that local changes in filopodial PY levels may underlie growth cone pathfinding decisions. p21-activated kinase (PAK), a Cdc42 effector whose activity is regulated by Src phosphorylation, also localizes to the tips of extending filopodia and controls filopodial motility. Coordinated activation of cytoskeletal effector proteins by GTPase binding and Src-mediated tyrosine phosphorylation may function to produce specific growth cone behaviors in response to guidance cues.

Animals↗

PubMed2004

The great escape; phosphorylation of Ena/VASP by PKA promotes filopodial formation.

The Ena/VASP family of proteins consists of adaptor molecules that localize to subcellular sites of actin polymerization. The role of Ena/VASP proteins in the regulation of cell motility and axon outgrowth has been controversial. Recently, these proteins have been proposed to function as "anticapping" factors, which may have differential effects on filopodial versus lammelipodial actin-based protrusions. A study by Lebrand et al. in this issue of Neuron supports this model and identifies PKA as a key regulator of Ena/VASP function downstream of the chemoattractant Netrin.

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PubMed2003

Filopodial calcium transients regulate growth cone motility and guidance through local activation of calpain.

Spontaneous intracellular calcium ([Ca2+](i)) transients in growth cone filopodia reduce filopodial motility, slow neurite outgrowth, and promote turning when generated asymmetrically; however, the downstream effectors of these Ca2+ -dependent behaviors are unknown. We report that Ca2+ transients in filopodia activate the intracellular protease calpain, which slows neurite outgrowth and promotes repulsive growth cone turning upon local activation. Active calpain alters the balance between tyrosine kinase and phosphatase activities in filopodia, resulting in a net decrease in tyrosine phosphorylation, which mediates both filopodial stabilization and reduced lamellipodial protrusion. Our findings indicate that locally generated Ca2+ signals repel axon outgrowth through calpain-dependent regulation of phosphotyrosine signaling at integrin-mediated adhesion sites.

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