Publicação
Post-translational regulation of Ascl1 during neurogenesis
| Resumo: | Neurogenesis in vertebrates is to a large extent regulated by proneural transcriptional factors (TFs) such as Ascl1. Ascl1 is expressed in the germinal layers of the ventral telencephalon, promoting sequentially the proliferation and differentiation of neural stem/progenitors throughout the neuronal lineage. Ac cording to the current model an increase in Ascl1 activity determines the onset of neuronal differentia tion. Multisite phosphorylation of proneural TFs in Serine/Proline (SP) sites outside the DNA-binding domain has been proposed to decrease neurogenic activity, by changing their overall electrostatic po tential. O-GlcNAcylation, a neutrally charged PTM catalyzed by O-GlcNAc transferase OGT, can counteract phosphorylation by targeting the same residues. Few studies have implicated O-GlcNAcyl ation in neurogenesis regulation, but the exact mechanisms (and how this may impact Ascl1 activity) is not known. Here, using western-blot analysis we show for the first time that endogenous Ascl1 protein is highly phosphorylated in neural stem/progenitors in culture, and in the embryonic ventral telencephalon. Additionally, we observe a decrease in Ascl1 phosphorylation during neuronal differentiation. Preliminary results, using overexpression of a phosphodead version of Ascl1 (with six SP sites mutated), suggest multisite phosphorylation does not impact protein stability, but results in an increase in its cytoplasmic and chromatin bound fractions. This is in line with the possibility that multisite phosphorylation decreases Ascl1 activity, by reducing its association with negatively charged chromatin. Furthermore, we used immunofluorescence and western-blot analysis to characterize O GlcNAcylation in cultured neural stem/progenitor cells. We found O-GlcNAc is predominantly nuclear, becoming even more nuclear during neuronal differentiation. Unexpectedly, we found that a pharmacological inhibitor of O-GlcNAc transferase (OGT) drastically reduces Ascl1 protein levels in cultured neural stem/progenitor cells. Additionally, co-expression of OGT with Ascl1 (tethered to its heterodimeric partner E47) indicates Ascl1/E47 heterodimers can be targeted by O-GlcNAcylation. This suggests different mechanisms by which O-GlcNAcylation may regulate Ascl1, which should be further investigated. |
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| Autores principais: | Marques, Raquel Forte |
| Assunto: | Fosforilação O-glicosilação Diferenciação Neuronal Carga das proteinas Ligação á cromatina Teses de mestrado - 2022 |
| Ano: | 2022 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | Neurogenesis in vertebrates is to a large extent regulated by proneural transcriptional factors (TFs) such as Ascl1. Ascl1 is expressed in the germinal layers of the ventral telencephalon, promoting sequentially the proliferation and differentiation of neural stem/progenitors throughout the neuronal lineage. Ac cording to the current model an increase in Ascl1 activity determines the onset of neuronal differentia tion. Multisite phosphorylation of proneural TFs in Serine/Proline (SP) sites outside the DNA-binding domain has been proposed to decrease neurogenic activity, by changing their overall electrostatic po tential. O-GlcNAcylation, a neutrally charged PTM catalyzed by O-GlcNAc transferase OGT, can counteract phosphorylation by targeting the same residues. Few studies have implicated O-GlcNAcyl ation in neurogenesis regulation, but the exact mechanisms (and how this may impact Ascl1 activity) is not known. Here, using western-blot analysis we show for the first time that endogenous Ascl1 protein is highly phosphorylated in neural stem/progenitors in culture, and in the embryonic ventral telencephalon. Additionally, we observe a decrease in Ascl1 phosphorylation during neuronal differentiation. Preliminary results, using overexpression of a phosphodead version of Ascl1 (with six SP sites mutated), suggest multisite phosphorylation does not impact protein stability, but results in an increase in its cytoplasmic and chromatin bound fractions. This is in line with the possibility that multisite phosphorylation decreases Ascl1 activity, by reducing its association with negatively charged chromatin. Furthermore, we used immunofluorescence and western-blot analysis to characterize O GlcNAcylation in cultured neural stem/progenitor cells. We found O-GlcNAc is predominantly nuclear, becoming even more nuclear during neuronal differentiation. Unexpectedly, we found that a pharmacological inhibitor of O-GlcNAc transferase (OGT) drastically reduces Ascl1 protein levels in cultured neural stem/progenitor cells. Additionally, co-expression of OGT with Ascl1 (tethered to its heterodimeric partner E47) indicates Ascl1/E47 heterodimers can be targeted by O-GlcNAcylation. This suggests different mechanisms by which O-GlcNAcylation may regulate Ascl1, which should be further investigated. |
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