RESUMEN
The evolutionarily conserved JNK/AP-1 (Jun N-terminal kinase/activator protein 1) and BMP (Bone Morphogenetic Protein) signaling cascades are deployed hierarchically to regulate dorsal closure in the fruit fly Drosophila melanogaster. In this developmental context, the JNK/AP-1 signaling cascade transcriptionally activates BMP signaling in leading edge epidermal cells. Here we show that the mummy (mmy) gene product, which is required for dorsal closure, functions as a BMP signaling antagonist. Genetic and biochemical tests of Mmy's role as a BMP-antagonist indicate that its function is independent of AP-1, the transcriptional trigger of BMP signal transduction in leading edge cells. pMAD (phosphorylated Mothers Against Dpp) activity data show the mmy gene product to be a new type of epidermal BMP regulator - one which transforms a BMP ligand from a long- to a short-range signal. mmy codes for the single UDP-N-acetylglucosamine pyrophosphorylase in Drosophila, and its requirement for attenuating epidermal BMP signaling during dorsal closure points to a new role for glycosylation in defining a highly restricted BMP activity field in the fly. These findings add a new dimension to our understanding of mechanisms modulating the BMP signaling gradient.
Asunto(s)
Proteínas de Drosophila/metabolismo , Drosophila melanogaster/enzimología , Regulación del Desarrollo de la Expresión Génica , Nucleotidiltransferasas/metabolismo , Secuencia de Aminoácidos , Animales , Proteínas Morfogenéticas Óseas/genética , Proteínas Morfogenéticas Óseas/metabolismo , Proteínas de Drosophila/genética , Drosophila melanogaster/embriología , Drosophila melanogaster/genética , Embrión no Mamífero/metabolismo , Desarrollo Embrionario , Activación Enzimática , Epidermis/metabolismo , Epidermis/patología , Glicosilación , Sistema de Señalización de MAP Quinasas , Datos de Secuencia Molecular , Nucleotidiltransferasas/genética , Organismos Modificados Genéticamente/embriología , Organismos Modificados Genéticamente/genética , Organismos Modificados Genéticamente/metabolismo , Estructura Terciaria de Proteína , Factores de Tiempo , Factor de Transcripción AP-1/genética , Factor de Transcripción AP-1/metabolismoRESUMEN
High baselines of transcription factor activities represent fundamental obstacles to regulated signaling. Here we show that in Drosophila, quenching of basal activator protein 1 (AP-1) transcription factor activity serves as a prerequisite to its tight spatial and temporal control by the JNK (Jun N-terminal kinase) signaling cascade. Our studies indicate that the novel raw gene product is required to limit AP-1 activity to leading edge epidermal cells during embryonic dorsal closure. In addition, we provide the first evidence that the epidermis has a Basket JNK-independent capacity to activate AP-1 targets and that raw function is required broadly throughout the epidermis to antagonize this activity. Finally, our mechanistic studies of the three dorsal-open group genes [raw, ribbon (rib), and puckered (puc)] indicate that these gene products provide at least two tiers of JNK/AP-1 regulation. In addition to Puckered phosphatase function in leading edge epidermal cells as a negative-feedback regulator of JNK signaling, the three dorsal-open group gene products (Raw, Ribbon, and Puckered) are required more broadly in the dorsolateral epidermis to quench a basal, signaling-independent activity of the AP-1 transcription factor.
