RESUMEN
Development of an organism requires accurate coordination between the growth of a tissue and orientation of cells within the tissue. The large cadherin Fat has been shown to play a role in both of these processes. Fat is involved in the establishment of planar cell polarity and regulates growth through the Hippo pathway, a developmental cascade that controls proliferation and apoptosis. Both Fat and the Hippo pathway are known to regulate transcription of four-jointed, although the nature of this regulation is unknown. In this study, we test whether Fat affects four-jointed transcription via or independently of Hippo pathway. Our analysis of the four-jointed regulatory region reveals a 1.2â¯kb element that functions as an enhancer for graded expression of Four-jointed in the eye imaginal disc. Within this enhancer element, we identify a 20 bp fragment that is critical for regulation by Fat but not by Hippo. Our findings suggest that Fat and the Hippo pathway control four-jointed expression independently of each other and none of the transcription factors known to function downstream of the Hippo pathway are required to regulate four-jointed expression through the 1.2â¯kb element.
Asunto(s)
Moléculas de Adhesión Celular , Proteínas de Drosophila , Elementos de Facilitación Genéticos , Regulación del Desarrollo de la Expresión Génica , Péptidos y Proteínas de Señalización Intracelular , Glicoproteínas de Membrana , Proteínas Serina-Treonina Quinasas , Transducción de Señal , Transcripción Genética , Animales , Moléculas de Adhesión Celular/genética , Moléculas de Adhesión Celular/metabolismo , Proteínas de Drosophila/biosíntesis , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster , Genes Reporteros , Péptidos y Proteínas de Señalización Intracelular/genética , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Glicoproteínas de Membrana/biosíntesis , Glicoproteínas de Membrana/genética , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/metabolismoRESUMEN
The Drosophila tumor suppressor gene fat encodes a large cadherin that regulates growth and a form of tissue organization known as planar cell polarity (PCP). Fat regulates growth via the Hippo kinase pathway, which controls expression of genes promoting cell proliferation and inhibiting apoptosis (reviewed in). The Hippo pathway is highly conserved and is implicated in the regulation of mammalian growth and cancer development. Genetic studies suggest that Fat activity is regulated by binding to another large cadherin, Dachsous (Ds). The tumor suppressor discs overgrown (dco)/Casein Kinase I delta/epsilon also regulates Hippo activity and PCP. The biochemical nature of how Fat, Ds, and Dco interact to regulate these pathways is poorly understood. Here we demonstrate that Fat is cleaved to generate 450 kDa and 110 kDa fragments (Fat(450) and Fat(110)). Fat(110) contains the cytoplasmic and transmembrane domain. The cytoplasmic domain of Fat binds Dco and is phosphorylated by Dco at multiple sites. Importantly, we show Fat forms cis-dimers and that Fat phosphorylation is regulated by Dachsous and Dco in vivo. We propose that Ds regulates Dco-dependent phosphorylation of Fat and Fat-associated proteins to control Fat signaling in growth and PCP.
Asunto(s)
Cadherinas/metabolismo , Caseína Cinasa 1 épsilon/metabolismo , Moléculas de Adhesión Celular/metabolismo , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/fisiología , Secuencia de Aminoácidos , Animales , Cadherinas/genética , Caseína Cinasa 1 épsilon/genética , Quinasa Idelta de la Caseína/genética , Quinasa Idelta de la Caseína/metabolismo , Moléculas de Adhesión Celular/genética , Línea Celular , Polaridad Celular , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Células Madre Embrionarias/citología , Células Madre Embrionarias/fisiología , Humanos , Péptidos y Proteínas de Señalización Intracelular/genética , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Ligandos , Ratones , Datos de Secuencia Molecular , Fosforilación , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Procesamiento Proteico-Postraduccional , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , TransgenesRESUMEN
High levels of interspecies conservation characterise all signal transduction cascades and demonstrate the significance of these pathways over evolutionary time. Here, we review advances in the field of JAK/STAT signalling, focusing on recent developments in Drosophila. In particular, recent results from genetic and genome-wide RNAi screens, as well as studies into the developmental roles played by this pathway, highlight striking levels of physical and functional conservation in processes such as cellular proliferation, immune responses and stem cell maintenance. These insights underscore the value of model organisms for improving our understanding of this human disease-relevant pathway.
Asunto(s)
Proteínas de Drosophila/metabolismo , Drosophila melanogaster/fisiología , Proteínas Tirosina Quinasas/metabolismo , Factores de Transcripción STAT/metabolismo , Transducción de Señal/fisiología , Factores de Transcripción/metabolismo , Animales , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Proteínas de Drosophila/genética , Drosophila melanogaster/anatomía & histología , Drosophila melanogaster/embriología , Drosophila melanogaster/crecimiento & desarrollo , Humanos , Quinasas Janus , Proteínas Inhibidoras de STAT Activados/genética , Proteínas Inhibidoras de STAT Activados/metabolismo , Proteínas Tirosina Quinasas/genética , Factores de Transcripción STAT/genética , Células Madre/citología , Células Madre/fisiología , Proteínas Supresoras de la Señalización de Citocinas/genética , Proteínas Supresoras de la Señalización de Citocinas/metabolismo , Factores de Transcripción/genéticaRESUMEN
A limited number of evolutionarily conserved signal transduction pathways are repeatedly reused during development to regulate a wide range of processes. Here we describe a new negative regulator of JAK/STAT signaling and identify a potential mechanism by which the pleiotropy of responses resulting from pathway activation is generated in vivo. As part of a genetic interaction screen, we have identified Ken & Barbie (Ken) , which is an ortholog of the mammalian proto-oncogene BCL6 , as a negative regulator of the JAK/STAT pathway. Ken genetically interacts with the pathway in vivo and recognizes a DNA consensus sequence overlapping that of STAT92E in vitro. Tissue culture-based assays demonstrate the existence of Ken-sensitive and Ken-insensitive STAT92E binding sites, while ectopically expressed Ken is sufficient to downregulate a subset of JAK/STAT pathway target genes in vivo. Finally, we show that endogenous Ken specifically represses JAK/STAT-dependent expression of ventral veins lacking (vvl) in the posterior spiracles. Ken therefore represents a novel regulator of JAK/STAT signaling whose dynamic spatial and temporal expression is capable of selectively modulating the transcriptional repertoire elicited by activated STAT92E in vivo.
