RESUMEN
Protein homeostasis serves as an important step in regulating diverse cellular processes underlying the function and development of the nervous system. In particular, the ubiquitination proteasome system (UPS), a universal pathway mediating protein degradation, contributes to the development of numerous synaptic structures, including the Drosophila olfactory-associative learning center mushroom body (MB), thereby affecting associated function. Here, we describe the function of a newly characterized Drosophila F-box protein CG5003, an adaptor for the RING-domain type E3 ligase (SCF complex), in MB development. Lacking CG5003 ubiquitously causes MB γ axon pruning defects and selective CG5003 expression in pan-neurons leads to both γ axon and α/ß lobe abnormalities. Interestingly, change in CG5003 expression in MB neurons does not cause any abnormalities in axons, suggesting that CG5003 functions in cells extrinsic to MB to regulate its development. Mass spectrum analysis indicates that silencing CG5003 expression in all neurons affects expression levels of proteins in the cell and structural morphogenesis, transcription regulator activity, and catalytic activity. Our findings reinforce the importance of UPS and identify a new factor in regulating neuronal development as exemplified by the synaptic structure MB.
RESUMEN
Canonical Wnt/ß-catenin signaling pathway plays important roles in multiple aspects of cellular responses in development and diseases. It is currently thought that Wnt receptor Frizzled (Frz) exists separately to Wnt coreceptors LRP5 and LRP6 (LRP5/6), and that Wnt-Frz-LRP5/6 triple complex formation bridged by Wnt ligand is needed for canonical pathway activation. We recently showed that Frz and LRP5/6 interact with each other in the absence of Wnt ligand binding and this interaction maintains the Frz-LRP5/6 complex in an inactive state. Here, we further show that Wnt ligand stimulation induces conformational change of the Frz-LRP6 complex and leads to hexamer formation containing the core LDLR domain-mediated LRP6 homodimer that is stabilized by two pairs of Wnt3a and Frz8, that is, Wnt3a-Frz8-LRP6-LRP6-Frz8-Wnt3a. This LDLR-mediated LRP6 dimerization is essential for robust canonical Wnt pathway activation. Our study thus suggests a previously unrecognized mode of receptor interaction in Wnt signal initiation.
Asunto(s)
Proteína-6 Relacionada a Receptor de Lipoproteína de Baja Densidad/metabolismo , Receptores de LDL/metabolismo , Proteína Wnt3A/metabolismo , Secuencia de Aminoácidos , Dimerización , Receptores Frizzled/metabolismo , Células HEK293 , Células Hep G2 , Humanos , Ligandos , Proteína-5 Relacionada con Receptor de Lipoproteína de Baja Densidad/metabolismo , Datos de Secuencia Molecular , Receptores de LDL/química , Vía de Señalización Wnt , Proteína Wnt3A/química , beta Catenina/metabolismoRESUMEN
Gliogenesis in animal development is spatiotemporally regulated so that correct numbers of glia are present to support various neuronal functions. During Drosophila embryonic development, the glial regulatory gene, glial cell missing/glial cell deficient (gcm/glide), promotes glial cell fate and differentiation. Here we describe the ubiquitin-proteasome regulation of the Gcm protein and the consequence in gliogenesis without timely degradation of Gcm. Gcm binds to 2 F-box proteins, Supernumerary limbs (Slimb) and Archipelago (Ago), adaptors of SCF E3 ubiquitin ligases. Ubiquitination and proteasomal degradation of Gcm depend on slimb and ago. In slimb and ago double mutants, Gcm protein levels are enhanced. Concomitantly, glial cell numbers increase owing to proliferation, which can be phenocopied by Gcm overexpression only at the onset of glial differentiation. The glial lineage 5-6A in slimb ago mutants displays excess glial progenies and enhanced Gcm protein levels. We propose that downregulation of Gcm protein levels by Slimb and Ago is required for glial progenitors to exit the cell cycle for differentiation.