RESUMO
Planar cell polarity (PCP) is a common feature in many epithelia, reflected in cellular organization within the plane of an epithelium. In the Drosophila eye, Frizzled (Fz)/PCP signaling induces cell-fate specification of the R3/R4 photoreceptors through regulation of Notch activation in R4. Except for Dl upregulation in R3, the mechanism of how Fz/PCP signaling regulates Notch in this context is not understood. We demonstrate that the E3-ubiquitin ligase Neuralized (Neur), required for Dl-N signaling, is asymmetrically expressed within the R3/R4 pair. It is required in R3, where it is also upregulated in a Fz/PCP-dependent manner. As is the case for Dl, N activity in R4 further represses neur expression, thus, reinforcing the asymmetry. We demonstrate that Neur asymmetry is instructive in correct R3/R4 specification. Our data indicate that Fz/PCP-dependent Neur expression in R3 ensures the proper directionality of Dl-N signaling during R3/R4 specification.
Assuntos
Polaridade Celular , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/crescimento & desenvolvimento , Olho/embriologia , Receptores Frizzled/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Receptores da Fenciclidina/metabolismo , Ubiquitina-Proteína Ligases/metabolismo , Animais , Animais Geneticamente Modificados , Linhagem da Célula , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Olho/metabolismo , Imunofluorescência , Receptores Frizzled/genética , Regulação da Expressão Gênica no Desenvolvimento , Peptídeos e Proteínas de Sinalização Intracelular , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Células Fotorreceptoras de Invertebrados , Receptores Acoplados a Proteínas G/genética , Receptores Notch/genética , Receptores Notch/metabolismo , Receptores da Fenciclidina/genética , Transdução de Sinais , Ubiquitina-Proteína Ligases/genéticaRESUMO
The studies described demonstrate that rat brain mRNA directs the synthesis of at least four types of functional EAA receptors in the Xenopus oocyte system, whereas in this system NCB-20 cell mRNA directs the synthesis of only the NMDA type of EAA receptor. The NMDA channel expressed in the oocyte, using either rat brain mRNA or NCB-20 cell mRNA, exhibits the pharmacologic properties of the neuronal receptor, including the functional association with the PCP receptor located within the NMDA-gated channel. The demonstration that mRNA isolated from NCB-20 cells lacking functional NMDA-activated channels, but bearing PCP binding sites, can encode functional NMDA-activated channels in the oocyte indicates some defect or regulating step in posttranslational processing or insertion of the receptors into the plasma membrane in the cell of origin. This is the only cell line known to (1) have PCP receptors that appear to be associated with NMDA receptors and (2) provide a homogeneous, self-replicating population of cells that can be manipulated genetically and by changing the extracellular environment. Consequently, the NCB-20 cell line will be useful for the study of the NMDA receptor and its expression.