RESUMO
Ran's GTPase-activating protein (RanGAP) is tethered to the nuclear envelope (NE) in multicellular organisms. We investigated the consequences of RanGAP localization in human tissue culture cells and Drosophila. In tissue culture cells, disruption of RanGAP1 NE localization surprisingly has neither obvious impacts on viability nor nucleocytoplasmic transport of a model substrate. In Drosophila, we identified a region within nucleoporin dmRanBP2 required for direct tethering of dmRanGAP to the NE. A dmRanBP2 mutant lacking this region shows no apparent growth defects during larval stages but arrests at the early pupal stage. A direct fusion of dmRanGAP to the dmRanBP2 mutant rescues this arrest, indicating that dmRanGAP recruitment to dmRanBP2 per se is necessary for the pupal ecdysis sequence. Our results indicate that while the NE localization of RanGAP is widely conserved in multicellular organisms, the targeting mechanisms are not. Further, we find a requirement for this localization during pupal development.
Assuntos
Proteínas de Drosophila/metabolismo , Drosophila melanogaster/crescimento & desenvolvimento , Proteínas Ativadoras de GTPase/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Chaperonas Moleculares/metabolismo , Membrana Nuclear/metabolismo , Complexo de Proteínas Formadoras de Poros Nucleares/metabolismo , Poro Nuclear/metabolismo , Pupa/crescimento & desenvolvimento , Transporte Ativo do Núcleo Celular , Animais , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Proteínas Ativadoras de GTPase/genética , Células HCT116 , Humanos , Chaperonas Moleculares/genética , Membrana Nuclear/genética , Poro Nuclear/genética , Complexo de Proteínas Formadoras de Poros Nucleares/genética , Pupa/genética , Pupa/metabolismoRESUMO
The maintenance of the intestinal epithelium is ensured by the controlled proliferation of intestinal stem cells (ISCs) and differentiation of their progeny into various cell types, including enterocytes (ECs) that both mediate nutrient absorption and provide a barrier against pathogens. The signals that regulate transition of proliferative ISCs into differentiated ECs are not fully understood. IRBIT is an evolutionarily conserved protein that regulates ribonucleotide reductase (RNR), an enzyme critical for the generation of DNA precursors. Here, we show that IRBIT expression in ISC progeny within the Drosophila midgut epithelium cells regulates their differentiation via suppression of RNR activity. Disruption of this IRBIT-RNR regulatory circuit causes a premature loss of intestinal tissue integrity. Furthermore, age-related dysplasia can be reversed by suppression of RNR activity in ISC progeny. Collectively, our findings demonstrate a role of the IRBIT-RNR pathway in gut homeostasis.
