Biology subjects

Sharif, J.

Publications and source records attributed to Sharif, J..

3 recordsLinked to original sources

bioRxiv2022

HP1 deficiency results in De-Repression of Endogenous Retroviruses and Induction of Neurodegeneration via Complement

In aging cells and animal models of premature aging, heterochromatin loss coincides with transcriptional disruption including the activation of normally silenced endogenous retroviruses (ERVs). Here we show that loss of heterochromatin maintenance and de-repression of ERVs results in a chronic inflammatory environment characterized by neurodegeneration and cognitive decline. We discovered differential contributions of HP1 proteins to ERV silencing where HP1{gamma} is necessary and sufficient for H4K20me3 deposition and HP1{beta} deficiency causes aberrant DNA methylation. Combined loss of HP1{beta} and HP1{gamma} resulted in loss of DNA methylation at ERVK elements. Progressive ERV de-repression in HP1{beta}/{gamma} DKO mice was followed by stimulation of the integrated stress response, an increase of Complement 3+ reactive astrocytes and phagocytic microglia. This chronic inflammatory state coincided with age-dependent reductions in dendrite complexity and cognition. Our results demonstrate the importance of preventing loss of epigenetic maintenance, as this will be the only way postmitotic neuronal genomes can be protected and/or renewed. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/505641v4_ufig1.gif" ALT="Figure 1"> View larger version (65K): org.highwire.dtl.DTLVardef@f5feb7org.highwire.dtl.DTLVardef@25d73dorg.highwire.dtl.DTLVardef@5604a4org.highwire.dtl.DTLVardef@14ad84a_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2022

Structural basis for activation of DNMT1

DNMT1 is an essential enzyme that maintains genomic DNA methylation, and its function is regulated by mechanisms that are not yet fully understood. Here, we report the cryo-EM structure of human DNMT1 bound to its two natural activators: hemimethylated DNA and ubiquitinated histone H3. We find that a hitherto unstudied linker, between the RFTS and CXXC domains, plays a key role for activation. It contains a conserved -helix which engages a crucial "Toggle" pocket, displacing a previously described inhibitory linker, and allowing the DNA recognition helix to spring into the active conformation. This is accompanied by large-scale reorganization of the inhibitory RFTS and CXXC domains, allowing the enzyme to gain full activity. Our results therefore provide a mechanistic basis for the activation of DNMT1, with consequences for basic research and drug design.

biochemistry↗

bioRxiv2022

Microglia integration into human midbrain organoids leads to increased neuronal maturation and functionality.

The human brain is a complex, three-dimensional structure. To better recapitulate brain complexity, recent efforts have focused on the development of human specific midbrain organoids. Human iPSC-derived midbrain organoids consist of differentiated and functional neurons, which contain active synapses, as well as astrocytes and oligodendrocytes. However, the absence of microglia, with their ability to remodel neuronal networks and phagocytose apoptotic cells and debris, represents a major disadvantage for the current midbrain organoid systems. Additionally, neuro-inflammation related disease modeling is not possible in the absence of microglia. So far, no studies about the effects of human iPSC-derived microglia on midbrain organoid neural cells have been published. Here we describe an approach to derive microglia from human iPSCs and integrate them into iPSC-derived midbrain organoids. Using single nuclear RNA Sequencing, we provide a detailed characterization of microglia in midbrain organoids as well as the influence of their presence on the other cells of the organoids. Furthermore, we describe the effects that microglia have on cell death and oxidative stress- related gene expression. Finally, we show that microglia in midbrain organoids affect synaptic remodeling and increase neuronal excitability. Altogether, we show a more suitable system to further investigate brain development, as well as neurodegenerative diseases and neuro- inflammation. Main Points- Macrophage precursors can be efficiently co-cultured with midbrain organoids, they integrate into the tissue and differentiate into microglia in 3D. - Organoids containing microglia have a smaller size and show a down-regulation of oxidative stress-related genes. - Organoids co-cultured with microglia show differences in genes related to synaptic remodeling and action potential, as well as a more spontaneous action potential firing.

neuroscience↗