Distinct CoREST complexes act in a cell-type-specific manner

A germline PAF1 paralog complex ensures cell type-specific gene expression

Animal germline development and fertility rely on paralogs of general transcription factors that recruit RNA polymerase II to ensure cell type-specific gene expression. It remains unclear whether gene expression processes downstream from such paralog-based transcription is distinct from that of canonical RNA polymerase II genes. In Drosophila, the testis-specific TBP-associated factors (tTAFs) activate over a thousand spermatocyte-specific gene promoters to enable meiosis and germ cell differentiation. Here, we show that efficient termination of tTAF-activated transcription relies on testis-specific paralogs of canonical polymerase-associated factor 1 complex (PAF1C) proteins, which form a testis-specific PAF1C (tPAF). Consequently, tPAF mutants show aberrant expression of hundreds of downstream genes due to read-in transcription. Furthermore, tPAF facilitates expression of Y-linked male fertility factor genes and thus serves to maintain spermatocyte-specific gene expression. Consistently, tPAF is required for the segregation of meiotic chromosomes and male fertility. Supported by comparative in vivo protein interaction assays, we provide a mechanistic model for the functional divergence of tPAF and the PAF1C and identify transcription termination as a developmentally regulated process required for germline-specific gene expression.

SPR-1/CoREST facilitates the maternal epigenetic reprogramming of the histone demethylase SPR-5/LSD1

Maternal reprogramming of histone methylation is critical for reestablishing totipotency in the zygote, but how histone-modifying enzymes are regulated during maternal reprogramming is not well characterized. To address this gap, we asked whether maternal reprogramming by the H3K4me1/2 demethylase SPR-5/LSD1/KDM1A, is regulated by the chromatin co-repressor protein, SPR-1/CoREST, in Caenorhabditis elegans and mice. In C. elegans, SPR-5 functions as part of a reprogramming switch together with the H3K9 methyltransferase MET-2. By examining germline development, fertility, and gene expression in double mutants between spr-1 and met-2, as well as fertility in double mutants between spr-1 and spr-5, we find that loss of SPR-1 results in a partial loss of SPR-5 maternal reprogramming function. In mice, we generated a separation of function Lsd1 M448V point mutation that compromises CoREST binding, but only slightly affects LSD1 demethylase activity. When maternal LSD1 in the oocyte is derived exclusively from this allele, the progeny phenocopy the increased perinatal lethality that we previously observed when LSD1 was reduced maternally. Together, these data are consistent with CoREST having a conserved function in facilitating maternal LSD1 epigenetic reprogramming.

A developmental role for the chromatin-regulating CoREST complex in the cnidarian Nematostella vectensis

BACKGROUND

Chromatin-modifying proteins are key players in the regulation of development and cell differentiation in animals. Most chromatin modifiers, however, predate the evolution of animal multicellularity, and how they gained new functions and became integrated into the regulatory networks underlying development is unclear. One way this may occur is the evolution of new scaffolding proteins that integrate multiple chromatin regulators into larger complexes that facilitate coordinated deposition or removal of different chromatin modifications. We test this hypothesis by analyzing the evolution of the CoREST-Lsd1-HDAC complex.

RESULTS

Using phylogenetic analyses, we show that a bona fide CoREST homolog is found only in choanoflagellates and animals. We then use the sea anemone Nematostella vectensis as a model for early branching metazoans and identify a conserved CoREST complex by immunoprecipitation and mass spectrometry of an endogenously tagged Lsd1 allele. In addition to CoREST, Lsd1 and HDAC1/2 this complex contains homologs of HMG20A/B and PHF21A, two subunits that have previously only been identified in mammalian CoREST complexes. NvCoREST expression overlaps fully with that of NvLsd1 throughout development, with higher levels in differentiated neural cells. NvCoREST mutants, generated using CRISPR-Cas9, fail to develop beyond the primary polyp stage, thereby revealing essential roles during development and for the differentiation of cnidocytes that phenocopy NvLsd1 mutants. We also show that this requirement is cell autonomous using a cell-type-specific rescue approach.

CONCLUSIONS

The identification of a Nematostella CoREST-Lsd1-HDAC1/2 complex, its similarity in composition with the vertebrate complex, and the near-identical expression patterns and mutant phenotypes of NvCoREST and NvLsd1 suggest that the complex was present before the last common cnidarian-bilaterian ancestor and thus represents an ancient component of the animal developmental toolkit.

Cross-Talk Between Histone Methyltransferases and Demethylases Regulate REST Transcription During Neurogenesis

The RE1 Silencing Transcription Factor (REST) is a major regulator of neurogenesis and brain development. Medulloblastoma (MB) is a pediatric brain cancer characterized by a blockade of neuronal specification. REST gene expression is aberrantly elevated in a subset of MBs that are driven by constitutive activation of sonic hedgehog (SHH) signaling in cerebellar granular progenitor cells (CGNPs), the cells of origin of this subgroup of tumors. To understand its transcriptional deregulation in MBs, we first studied control of Rest gene expression during neuronal differentiation of normal mouse CGNPs. Higher Rest expression was observed in proliferating CGNPs compared to differentiating neurons. Interestingly, two Rest isoforms were expressed in CGNPs, of which only one showed a significant reduction in expression during neurogenesis. In proliferating CGNPs, higher MLL4 and KDM7A activities opposed by the repressive polycomb repressive complex 2 (PRC2) and the G9A/G9A-like protein (GLP) complex function allowed Rest homeostasis. During differentiation, reduction in MLL4 enrichment on chromatin, in conjunction with an increase in PRC2/G9A/GLP/KDM7A activities promoted a decline in Rest expression. These findings suggest a lineage-context specific paradoxical role for KDM7A in the regulation of Rest expression in CGNPs. In human SHH-MBs (SHH-α and SHH-β) where elevated REST gene expression is associated with poor prognosis, up- or downregulation of KDM7A caused a significant worsening in patient survival. Our studies are the first to implicate KDM7A in REST regulation and in MB biology.

LSD1 Facilitates Pro-Inflammatory Polarization of Macrophages by Repressing Catalase

The increased level of hydrogen peroxide accompanies some modes of macrophage specification and is linked to ROS-based antimicrobial activity of these phagocytes. In this study, we show that activation of toll-like receptors with bacterial components such as LPS is accompanied by the decline in transcription of hydrogen peroxide decomposing enzyme-catalase, suppression of which facilitates the polarization of human macrophages towards the pro-inflammatory phenotype. The chromatin remodeling at the CAT promoter involves LSD1 and HDAC1, but activity of the first enzyme defines abundance of the two proteins on chromatin, histone acetylation status and the CAT transcription. LSD1 inhibition prior to macrophage activation with LPS prevents CAT repression by enhancing the LSD1 and interfering with the HDAC1 recruitment to the gene promoter. The maintenance of catalase level with LSD1 inhibitors during M1 polarization considerably limits LPS-triggered expression of some pro-inflammatory cytokines and markers such as IL1β, TNFα, COX2, CD14, TLR2, and IFNAR, but the effect of LSD1 inhibitors is lost upon catalase deficiency. Summarizing, activity of LSD1 allows for the CAT repression in LPS stimulated macrophages, which negatively controls expression of some key pro-inflammatory markers. LSD1 inhibitors can be considered as possible immunosuppressive drugs capable of limiting macrophage M1 specialization.

Crosstalk between cardiomyocytes and noncardiomyocytes is essential to prevent cardiomyocyte apoptosis induced by proteasome inhibition

Heart is a multi-cellular organ made up of various cell types interacting with each other. Cardiomyocytes may benefit or suffer from crosstalk with noncardiomyocytes in response to diverse kinds of cardiac stresses. Proteasome dysfunction is a common cardiac stress which causes cardiac proteotoxicity and contributes to cardiac diseases such as heart failure and myocardial infarction. The role of crosstalk between cardiomyocytes and noncardiomyocytes in defense of cardiac proteotoxicity remains unknown. Here, we report a cardiomyocyte-specific survival upon proteasome inhibition in a heterogeneous culture consisting of cardiomyocytes and other three major cardiac cell types. Conversely, cardiomyocyte apoptosis is remarkably induced by proteasome inhibition in a homogeneous culture consisting of a majority of cardiomyocytes, demonstrating an indispensable role of noncardiomyocytes in the prevention of cardiomyocyte apoptosis resulting from proteasome inhibition. We further show that cardiomyocytes express brain natriuretic peptide (BNP) as an extracellular molecule in response to proteasome inhibition. Blockade of BNP receptor on noncardiomyocytes significantly exacerbated the cardiomyocyte apoptosis, indicating a paracrine function of cardiomyocyte-released extracellular BNP in activation of a protective feedback from noncardiomyocytes. Finally, we demonstrate that proteasome inhibition-activated transcriptional up-regulation of BNP in cardiomyocytes was associated with the dissociation of repressor element 1 silencing transcription factor (REST)/ histone deacetylase 1 (HDAC1) repressor complex from BNP gene promoter. Consistently, the induction of BNP could be further augmented by the treatment of HDAC inhibitors. We conclude that the crosstalk between cardiomyocytes and noncardiomyocytes plays a crucial role in the protection of cardiomyocytes from proteotoxicity stress, and identify cardiomyocyte-released BNP as a novel paracrine signaling molecule mediating this crosstalk. These findings provide new insights into the key regulators and cardioprotective mechanism in proteasome dysfunction-related cardiac diseases.