RESUMO
Rac1 and RhoA are among the most widely studied small GTPases. The classic dogma surrounding their biology has largely focused on their activity as an "on/off switch" of sorts. However, the advent of more sophisticated techniques, such as genetically-encoded FRET-based sensors, has afforded the ability to delineate the spatiotemporal regulation of Rac1 and RhoA. As a result, there has been a shift from this simplistic global view to one incorporating the precision of spatiotemporal modularity. This review summarizes emerging data surrounding the roles of Rac1 and RhoA as cytoskeletal regulators and examines how these new data have led to a revision of the traditional dogma which placed Rac1 and RhoA in antagonistic pathways. This more recent evidence suggests that rather than absolute activity levels, it is the tight spatiotemporal regulation of Rac1 and RhoA across multiple roles, from oppositional to complementary, that is necessary to execute coordinated cytoskeletal processes affecting cell structure, function, and migration. We focus on how Kalirin and Trio, as dual GEFs that target Rac1 and RhoA, are uniquely designed to provide the spatiotemporally-precise shifts in Rac/Rho balance which mediate changes in neuronal structure and function, particularly by way of cytoskeletal rearrangements. Finally, we review how alterations in Trio and/or Kalirin function are associated with cellular abnormalities and neuropsychiatric disease.
Assuntos
Fatores de Troca do Nucleotídeo Guanina , Proteína rhoA de Ligação ao GTP , Citoesqueleto/metabolismo , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Proteínas rac1 de Ligação ao GTP/metabolismo , Proteína rhoA de Ligação ao GTP/metabolismoRESUMO
Coding junction formation in V(D)J recombination generates diversity in the antigen recognition structures of immunoglobulin and T-cell receptor molecules by combining processes of deletion of terminal coding sequences and addition of nucleotides prior to joining. We have examined the role of coding end DNA composition in junction formation with plasmid substrates containing defined homopolymers flanking the recombination signal sequence elements. We found that coding junctions formed efficiently with or without terminal DNA homology. The extent of junctional deletion was conserved independent of coding ends with increased, partial, or no DNA homology. Interestingly, G/C homopolymer coding ends showed reduced deletion regardless of DNA homology. Therefore, DNA homology cannot be the primary determinant that stabilizes coding end structures for processing and joining.
Assuntos
DNA/genética , Rearranjo Gênico , Genes de Imunoglobulinas , Variação Genética , Região de Junção de Imunoglobulinas/genética , Região Variável de Imunoglobulina/genética , Receptores de Antígenos de Linfócitos T/genética , Recombinação Genética , Animais , Sequência de Bases , Linhagem Celular , Clonagem Molecular , Drosophila/genética , Expressão Gênica , Proteínas de Choque Térmico/genética , Humanos , Linfoma de Células B , Dados de Sequência Molecular , Oligodesoxirribonucleotídeos , Mapeamento por Restrição , Deleção de Sequência , Homologia de Sequência do Ácido Nucleico , Células Tumorais CultivadasRESUMO
Lymphoid V(D)J rearrangement is targeted by recombination signal sequences (RSS) bordering V, D or J exons. We demonstrate that the DNA composition of flanking coding positions, particularly poly(A) or poly(T) stretches at one or both RSS, diminishes V(D)J recombination up to 100-fold. Positionally correct cleavages occur in the inhibited reactions, since the junctions formed show the same frequency of precision as uninhibited reactions. Open/shut cleavage/rejoining is not increased at a normal RSS in substrates containing inhibitory A/T homopolymers versus random sequence at a second RSS. Thus recombinase action at both cleavage sites is severely disrupted by modified coding sequences.
Assuntos
Rearranjo Gênico do Linfócito B/genética , Integrases , Recombinação Genética/genética , Linfócitos B/enzimologia , Sequência de Bases , DNA Nucleotidiltransferases/metabolismo , Dados de Sequência Molecular , Oligodesoxirribonucleotídeos/genética , Recombinases , Moldes Genéticos , Células Tumorais CultivadasRESUMO
Previous genetic studies of intersegmental nerve b development have identified several cell-surface proteins required for correct axon guidance to appropriate target muscles. Here we provide evidence that the small GTPase Drac1 also plays a key role in this guidance process. Neuronal expression of the dominant negative mutation Drac1(N17) causes axons to bypass and extend beyond normal synaptic partners. This phenotype is consistently reproduced by pharmacological blockade of actin assembly. Genetic interactions between Drac1(N17) and the receptor-tyrosine phosphatase Dlar suggest that intersegmental nerve b guidance requires the integration of multiple, convergent signals.