RESUMO
Laminins are heterotrimeric molecules found in all basement membranes. In mammals, they have been involved in diverse developmental processes, from gastrulation to tissue maintenance. The Drosophila genome encodes two laminin alpha chains, one beta and one Gamma, which form two distinct laminin trimers. So far, only mutations affecting one or other trimer have been analysed. In order to study embryonic development in the complete absence of laminins, we mutated the gene encoding the sole laminin beta chain in Drosophila, LanB1, so that no trimers can be made. We show that LanB1 mutant embryos develop until the end of embryogenesis. Electron microscopy analysis of mutant embryos reveals that the basement membranes are absent and the remaining extracellular material appears disorganised and diffuse. Accordingly, abnormal accumulation of major basement membrane components, such as Collagen IV and Perlecan, is observed in mutant tissues. In addition, we show that elimination of LanB1 prevents the normal morphogenesis of most organs and tissues, including the gut, trachea, muscles and nervous system. In spite of the above structural roles for laminins, our results unravel novel functions in cell adhesion, migration and rearrangement. We propose that while an early function of laminins in gastrulation is not conserved in Drosophila and mammals, their function in basement membrane assembly and organogenesis seems to be maintained throughout evolution.
Assuntos
Membrana Basal/fisiologia , Proteínas de Drosophila/fisiologia , Drosophila/embriologia , Embrião não Mamífero/fisiologia , Laminina/fisiologia , Animais , Membrana Basal/embriologia , Adesão Celular , Movimento Celular , Colágeno Tipo IV/metabolismo , Drosophila/fisiologia , Proteoglicanas de Heparan Sulfato/metabolismo , Morfogênese/genética , Mutação , Especificidade de ÓrgãosRESUMO
We report the functional characterization of the Drosophila ortholog of tensin, a protein implicated in linking integrins to the cytoskeleton and signaling pathways. A tensin null was generated and is viable with wing blisters, a phenotype characteristic of loss of integrin adhesion. In tensin mutants, mechanical abrasion is required during wing expansion to cause wing blisters, suggesting that tensin strengthens integrin adhesion. The localization of tensin requires integrins, talin, and integrin-linked kinase. The N-terminal domain and C-terminal PTB domain of tensin provide essential recruitment signals. The intervening SH2 domain is not localized on its own. We suggest a model where tensin is recruited to sites of integrin adhesion via its PTB and N-terminal domains, localizing the SH2 domain so that it can interact with phosphotyrosine-containing proteins, which stabilize the integrin link to the cytoskeleton.
Assuntos
Adesão Celular/fisiologia , Integrinas/fisiologia , Proteínas dos Microfilamentos/fisiologia , Animais , Animais Geneticamente Modificados , Adesão Celular/genética , Citoesqueleto/metabolismo , Drosophila/genética , Embrião não Mamífero , Proteína-Tirosina Quinases de Adesão Focal , Expressão Gênica , Regulação da Expressão Gênica no Desenvolvimento , Genes de Insetos/genética , Proteínas de Fluorescência Verde , Imuno-Histoquímica/métodos , Hibridização In Situ/métodos , Proteínas de Insetos/metabolismo , Integrinas/genética , Larva , Proteínas Luminescentes/metabolismo , Proteínas dos Microfilamentos/genética , Modelos Biológicos , Mutação , Fosfotirosina/metabolismo , Proteína de Ligação a Regiões Ricas em Polipirimidinas , Ligação Proteica , Proteínas Serina-Treonina Quinases/fisiologia , Proteínas Tirosina Quinases/metabolismo , RNA Mensageiro/biossíntese , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Estresse Fisiológico/genética , Estresse Fisiológico/metabolismo , Talina/fisiologia , Tensinas , Tirosina/metabolismo , Asas de Animais/embriologia , Asas de Animais/metabolismo , Domínios de Homologia de src/fisiologiaRESUMO
Integrins are cell surface receptors that mediate adhesion to the extracellular matrix. In this Perspective, we focus on the recent finding that a decrease in the levels of integrins yields fruit flies that retain youthful mobility as they age and display an increased mean life span. We discuss how the reduction of integrin activity might lead to the observed changes.