Project description:In most metazoan nuclei, heterochromatin is located at the nuclear periphery in contact with the nuclear lamina, which provides mechanical stability to the nucleus. We show that in cultured cells, chromatin de-compaction by the nucleosome binding protein HMGN5 decreases the sturdiness, elasticity, and rigidity of the nucleus. Mice overexpressing HMGN5, either globally or only in the heart, are normal at birth but develop hypertrophic heart with large cardiomyoctyes, deformed nuclei and disrupted lamina, and die of cardiac malfunction. Chromatin de-compaction is seen in cardiomyocytes of newborn mice but misshaped nuclei with disrupted lamina are seen only in adult cardiomyocytes, suggesting that loss of heterochromatin diminishes the ability of the nucleus to withstand the mechanical forces of the contracting heart. Thus, heterochromatin enhances the ability of the nuclear lamina to maintain the sturdiness and shape of the eukaryotic nucleus; a structural role for chromatin that is distinct from its genetic functions. The full length mouse Hmgn5 cDNA, containing the entire 5’ UTR and FLAG tag on the 3’ end was amplified by PCR and inserted between BglII and XhoI sites of the pCALL vector (Novak et al., 2000). This vector contains a floxed LacZ cDNA driven by the CAG (a hybrid CMV enhancer and chicken beta–actin) promoter which is highly active in early mouse embryos. The vector was linearized by NotI digestion and injected into fertilized oocytes of C57BL/6 mice. Total embryonic excision of LacZ sequence was done by breeding floxed HMGN5-TG mice with SoxCre mice (Hayashi et al., 2002). Heart-specific excision was performed by breeding floxed HMGN5-TG mice with alphaMHC-cre mice (Oka et al., 2006).Total RNA from the left ventricle of newborn and adult Hmgn5-hTG mice which overexpress HMGN5 only in the heart as well as control mice was collected from biological triplicates (duplicates, in the case of newborn wild-type mice) and analyzed by Affymetrix expression arrays.
Project description:In most metazoan nuclei, heterochromatin is located at the nuclear periphery in contact with the nuclear lamina, which provides mechanical stability to the nucleus. We show that in cultured cells, chromatin de-compaction by the nucleosome binding protein HMGN5 decreases the sturdiness, elasticity, and rigidity of the nucleus. Mice overexpressing HMGN5, either globally or only in the heart, are normal at birth but develop hypertrophic heart with large cardiomyoctyes, deformed nuclei and disrupted lamina, and die of cardiac malfunction. Chromatin de-compaction is seen in cardiomyocytes of newborn mice but misshaped nuclei with disrupted lamina are seen only in adult cardiomyocytes, suggesting that loss of heterochromatin diminishes the ability of the nucleus to withstand the mechanical forces of the contracting heart. Thus, heterochromatin enhances the ability of the nuclear lamina to maintain the sturdiness and shape of the eukaryotic nucleus; a structural role for chromatin that is distinct from its genetic functions.
Project description:The packaging of DNA into chromatin and its compaction within cells renders the underlying DNA template un-accessible for processes like transcription, replication and repair. Active mechanisms as chromatin modifying activities or the association with non-coding RNAs can de-condense chromatin, rendering it accessible for the DNA dependent processes. High mobility group proteins (HMG) are small architectural chromatin proteins that were shown to contribute to the regulation of chromatin accessibility and condensation. Here we show that HMGN5, a member of the HMGN family is capable to de-compact chromatin and to activate gene expression. We identified and characterized a novel RNA binding domain within HMGN5 that overlaps with its nucleosome binding domain (NBD). HMGN5 binds exclusively to nucleosomes or RNA, suggesting a switching mechanism and different functionalities depending on its binding partner. For this we show that HMGN5 is bound to regulatory regions of the genes that it tends to activate and also is found on the primary transcript of these genes. The results suggest that HMGN5 is switching from the chromatin binding to the RNA binding state after gene activation, potentially improving RNA synthesis. Furthermore, HMGN5 co-localizes and directly interacts with CTCF, suggesting a cooperative role of both proteins in organizing higher order structures of chromatin and active chromatin domains.
Project description:Neurons exploit mRNA localization and local translation to spatio-temporally regulate gene expression during development. Local translation and retrograde transport of transcription factors regulate nuclear gene expression in response to signaling events at distal neuronal ends. Whether epigenetic factors could also be involved in such regulation is not known. We report that the mRNA encoding the high mobility group N5 (HMGN5) chromatin binding protein localizes to growth cones of both neuronal-like cells and of hippocampal neurons. We show that Hmgn5 3’UTR drives growth cone localization and translation of a reporter gene, and that HMGN5 can be retrogradely transported into the nucleus along neurites. Loss of HMGN5 function induces transcriptional changes and impairs neurite outgrowth while HMGN5 overexpression induces neurite outgrowth and global chromatin decompaction. Interestingly, control of both neurite outgrowth and chromatin structure is dependent on proper growth cone localization of Hmgn5 mRNA. Our results provide the first evidence that mRNA localization and local translation might serve as a mechanism to couple the dynamic neuronal outgrowth process with chromatin regulation in the nucleus.
Project description:Neurons exploit local mRNA translation and retrograde transport of transcription factors to regulate gene expression in response to signaling events at distal neuronal ends. Whether epigenetic factors could also be involved in such regulation is not known. We report that the mRNA encoding the HMGN5 chromatin binding protein localizes to growth cones of both neuronal-like cells and of hippocampal neurons, where it has the potential to be translated, and that HMGN5 can be retrogradely transported into the nucleus along neurites. Loss of HMGN5 function induces transcriptional changes and impairs neurite outgrowth while HMGN5 overexpression induces neurite outgrowth and chromatin decompaction. Interestingly, control of both neurite outgrowth and chromatin structure is dependent on growth cone localization of Hmgn5 mRNA. Our results provide the first evidence that mRNA localization and local translation might serve as a mechanism to couple the dynamic neuronal outgrowth process with chromatin regulation in the nucleus.
Project description:HMGN5 is a member of the HMGN family that de-compacts chromatin and regulates gene expression. Chromatin-associated RNAs are known to play a major role in controlling gene expression and chromatin architecture. We recently showed that RNA is required to open chromatin structure in Drosophila. A potential involvement of RNA in the HMGN5-dependent opening of chromatin has not been studied so far. Here we revealed that HMGN5 has a novel and specific RNA binding activity, which is extended to the HMGN family. HMGN5 is associated preferentially with active regulatory regions and binds co-transcriptionally to the nascent RNA. Additionally, we showed that HMGN5 co-localizes and interacts with CTCF, which suggests a cooperative role of both proteins in organizing higher order structures of chromatin. We showed that HMGN5 forms mutually exclusive complexes with chromatin and RNA in vitro, altogether suggesting a dual role for HMGN5 in gene regulation, switching from nucleosome to RNA binding during gene activation.
Project description:HMGN5 is a member of the HMGN family that de-compacts chromatin and regulates gene expression. Chromatin-associated RNAs are known to play a major role in controlling gene expression and chromatin architecture. We recently showed that RNA is required to open chromatin structure in Drosophila. A potential involvement of RNA in the HMGN5-dependent opening of chromatin has not been studied so far. Here we revealed that HMGN5 has a novel and specific RNA binding activity, which is extended to the HMGN family. HMGN5 is associated preferentially with active regulatory regions and binds co-transcriptionally to the nascent RNA. Additionally, we showed that HMGN5 co-localizes and interacts with CTCF, which suggests a cooperative role of both proteins in organizing higher order structures of chromatin. We showed that HMGN5 forms mutually exclusive complexes with chromatin and RNA in vitro, altogether suggesting a dual role for HMGN5 in gene regulation, switching from nucleosome to RNA binding during gene activation.
Project description:HMGN5 is a member of the HMGN family that de-compacts chromatin and regulates gene expression. Chromatin-associated RNAs are known to play a major role in controlling gene expression and chromatin architecture. We recently showed that RNA is required to open chromatin structure in Drosophila. A potential involvement of RNA in the HMGN5-dependent opening of chromatin has not been studied so far. Here we revealed that HMGN5 has a novel and specific RNA binding activity, which is extended to the HMGN family. HMGN5 is associated preferentially with active regulatory regions and binds co-transcriptionally to the nascent RNA. Additionally, we showed that HMGN5 co-localizes and interacts with CTCF, which suggests a cooperative role of both proteins in organizing higher order structures of chromatin. We showed that HMGN5 forms mutually exclusive complexes with chromatin and RNA in vitro, altogether suggesting a dual role for HMGN5 in gene regulation, switching from nucleosome to RNA binding during gene activation.
Project description:Chromatin architectural protein NSBP1/HMGN5 belongs to the family of HMGN proteins which specifically interact with nucleosomes via Nucleosome Binding Domain, unfold chromatin and affect transcription. Mouse NSBP1 is a new and uncharacterized member of HMGN protein family. NSBP1 is a nuclear protein which is localized to euchromatin, binds to linker histone H1 and unfolds chromatin. We analyzed the effect of altered expression levels of mouse NSBP1 protein on global gene expression profile in AtT20 pituitary cells. We found that NSBP1 modulates the fidelity of cellular transcription in the nucleosome binding-dependent manner.