1 4838 140 ONCOGENIC N-RAS AND TET2 HAPLOINSUFFICIENCY COLLABORATE TO DYSREGULATE HEMATOPOIETIC STEM AND PROGENITOR CELLS. CONCURRENT GENETIC LESIONS EXIST IN A MAJORITY OF PATIENTS WITH HEMATOLOGIC MALIGNANCIES. AMONG THESE, SOMATIC MUTATIONS THAT ACTIVATE RAS ONCOGENES AND INACTIVATE THE EPIGENETIC MODIFIER TEN-ELEVEN TRANSLOCATION 2 (TET2) FREQUENTLY CO-OCCUR IN HUMAN CHRONIC MYELOMONOCYTIC LEUKEMIAS (CMMLS) AND ACUTE MYELOID LEUKEMIAS, SUGGESTING A COOPERATIVITY IN MALIGNANT TRANSFORMATION. TO TEST THIS, WE APPLIED A CONDITIONAL MURINE MODEL THAT ENDOGENOUSLY EXPRESSED ONCOGENIC NRAS(G12D) AND MONOALLELIC LOSS OF TET2 AND EXPLORED THE COLLABORATIVE ROLE SPECIFICALLY WITHIN HEMATOPOIETIC STEM AND PROGENITOR CELLS (HSPCS) AT DISEASE INITIATION. WE DEMONSTRATE THAT THE 2 MUTATIONS COLLABORATED TO ACCELERATE A TRANSPLANTABLE CMML-LIKE DISEASE IN VIVO, WITH AN OVERALL SHORTENED SURVIVAL AND INCREASED DISEASE PENETRANCE COMPARED WITH SINGLE MUTANTS. AT PRELEUKEMIC STAGE, N-RAS(G12D) AND TET2 HAPLOINSUFFICIENCY TOGETHER INDUCED BALANCED HEMATOPOIETIC STEM CELL (HSC) PROLIFERATION AND ENHANCED COMPETITIVENESS. NRAS(G12D/+)/TET2(+/-) HSCS DISPLAYED INCREASED SELF-RENEWAL IN PRIMARY AND SECONDARY TRANSPLANTATIONS, WITH SIGNIFICANTLY HIGHER RECONSTITUTION THAN SINGLE MUTANTS. STRIKINGLY, THE 2 MUTATIONS TOGETHER CONFERRED LONG-TERM RECONSTITUTION AND SELF-RENEWAL POTENTIAL TO MULTIPOTENT PROGENITORS, A POOL OF CELLS THAT USUALLY HAVE LIMITED SELF-RENEWAL COMPARED WITH HSCS. MOREOVER, HSPCS FROM NRAS(G12D/+)/TET2(+/-) MICE DISPLAYED INCREASED CYTOKINE SENSITIVITY IN RESPONSE TO THROMBOPOIETIN. THEREFORE, OUR STUDIES ESTABLISH A NOVEL TRACTABLE CMML MODEL AND PROVIDE INSIGHTS INTO HOW DYSREGULATED SIGNALING PATHWAYS AND EPIGENETIC MODIFIERS COLLABORATE TO MODULATE HSPC FUNCTION AND PROMOTE LEUKEMOGENESIS. 2018 2 5061 27 PHF6 FUNCTIONS AS A TUMOR SUPPRESSOR BY RECRUITING METHYLTRANSFERASE SUV39H1 TO NUCLEOLAR REGION AND OFFERS A NOVEL THERAPEUTIC TARGET FOR PHF6-MUNTANT LEUKEMIA. MUTATIONS IN THE PLANT HOMEODOMAIN-LIKE FINGER PROTEIN 6 (PHF6) GENE ARE STRONGLY ASSOCIATED WITH ACUTE MYELOID (AML) AND T-CELL ACUTE LYMPHOBLASTIC LEUKEMIA (T-ALL). IN THIS STUDY, WE DEMONSTRATED THAT PHF6 CAN BIND TO H3K9ME3 AND H3K27ME1 ON THE NUCLEOLAR CHROMATIN AND RECRUIT HISTONE METHYLTRANSFERASE SUV39H1 TO THE RDNA LOCUS. THE DELETION OF PHF6 CAUSED A DECREASE IN THE RECRUITMENT OF SUV39H1 TO RDNA GENE LOCI, RESULTING IN A REDUCTION IN THE LEVEL OF H3K9ME3 AND THE PROMOTION OF RDNA TRANSCRIPTION. THE KNOCKDOWN OF EITHER SUV39H1 OR PHF6 SIGNIFICANTLY ATTENUATED THE EFFECTS OF INCREASE IN H3K9ME3 AND SUPPRESSED THE TRANSCRIPTION OF RDNA INDUCED BY THE OVEREXPRESSION OF THE OTHER INTERACTING PARTNER, THEREBY ESTABLISHING AN INTERDEPENDENT RELATIONSHIP BETWEEN PHF6 AND SUV39H1 IN THEIR CONTROL OF RRNA TRANSCRIPTION. THE PHF6 CLINICAL MUTANTS SIGNIFICANTLY IMPAIRED THE ABILITY TO BIND AND RECRUIT SUV39H1 TO THE RDNA LOCI, RESULTING IN AN INCREASE IN RDNA TRANSCRIPTION ACTIVITY, THE PROLIFERATION OF IN VITRO LEUKEMIA CELLS, AND THE GROWTH OF IN VIVO MOUSE XENOGRAFTS. IMPORTANTLY, SIGNIFICANTLY ELEVATED LEVELS OF PRE-RRNA WERE OBSERVED IN CLINICAL AML PATIENTS WHO POSSESSED A MUTATED VERSION OF PHF6. THE SPECIFIC RDNA TRANSCRIPTION INHIBITOR CX5461 SIGNIFICANTLY REDUCED THE RESISTANCE OF U937 AML CELLS DEFICIENT IN PHF6 TO CYTARABINE, THE DRUG THAT IS MOST COMMONLY USED TO TREAT AML. COLLECTIVELY, WE REVEALED A NOVEL MOLECULAR MECHANISM BY WHICH PHF6 RECRUITS METHYLTRANSFERASE SUV39H1 TO THE NUCLEOLAR REGION IN LEUKEMIA AND PROVIDED A POTENTIAL THERAPEUTIC TARGET FOR PHF6-MUTANT LEUKEMIA. 2022 3 5789 43 SRSF2(P95H/+) CO-OPERATES WITH LOSS OF TET2 TO PROMOTE MYELOID BIAS AND INITIATE A CHRONIC MYELOMONOCYTIC LEUKEMIA-LIKE DISEASE IN MICE. RECURRENT MUTATIONS IN RNA SPLICING PROTEINS AND EPIGENETIC REGULATORS CONTRIBUTE TO THE DEVELOPMENT OF MYELODYSPLASTIC SYNDROME (MDS) AND RELATED MYELOID NEOPLASMS. IN CHRONIC MYELOMONOCYTIC LEUKEMIA (CMML), SRSF2 MUTATIONS OCCUR IN ~50% OF PATIENTS AND TET2 MUTATIONS IN ~60%. CLONAL ANALYSIS INDICATES THAT EITHER MUTATION CAN ARISE AS THE FOUNDER LESION. BASED ON HUMAN CANCER GENETICS WE CROSSED AN INDUCIBLE SRSF2(P95H/+) MUTANT MODEL WITH TET2(FL/FL) MICE TO MUTATE BOTH CONCOMITANTLY IN HEMATOPOIETIC STEM CELLS. AT 20-24 WEEKS POST MUTATION INDUCTION, WE OBSERVED SUBTLE DIFFERENCES IN THE SRSF2/TET2 MUTANTS COMPARED TO EITHER SINGLE MUTANT. UNDER CONDITIONS OF NATIVE HEMATOPOIESIS WITH AGING, WE SEE A DISTINCT MYELOID BIAS AND MONOCYTOSIS IN THE SRSF2/TET2 MUTANTS. A SUBSET OF THE COMPOUND SRSF2/TET2 MUTANTS DISPLAY AN INCREASED GRANULOCYTIC AND DISTINCTIVE MONOCYTIC PROLIFERATION (MYELOMONOCYTIC HYPERPLASIA), WITH INCREASED IMMATURE PROMONOCYTES AND MONOBLASTS AND BINUCLEATE PROMONOCYTES. EXOME ANALYSIS OF PROGRESSED DISEASE DEMONSTRATED MUTATIONS IN GENES AND PATHWAYS SIMILAR TO THOSE REPORTED IN HUMAN CMML. UPON TRANSPLANTATION, RECIPIENTS DEVELOPED LEUKOCYTOSIS, MONOCYTOSIS, AND SPLENOMEGALY. WE REPRODUCE SRSF2/TET2 CO-OPERATIVITY IN VIVO, YIELDING A DISEASE WITH CORE CHARACTERISTICS OF CMML, UNLIKE SINGLE SRSF2 OR TET2 MUTATION. THIS MODEL REPRESENTS A SIGNIFICANT STEP TOWARD BUILDING HIGH FIDELITY AND GENETICALLY TRACTABLE MODELS OF CMML. 2022 4 2647 22 EPIGENOMIC PLASTICITY OF ARABIDOPSIS MSH1 MUTANTS UNDER PROLONGED COLD STRESS. DYNAMIC TRANSCRIPTIONAL AND EPIGENETIC CHANGES ENABLE RAPID ADAPTIVE BENEFIT TO ENVIRONMENTAL FLUCTUATIONS. HOWEVER, THE UNDERLYING MECHANISMS AND THE EXTENT TO WHICH THIS OCCURS ARE NOT WELL KNOWN. MUTS HOMOLOG 1 (MSH1) MUTANTS CAUSE HERITABLE DEVELOPMENTAL PHENOTYPES ACCOMPANIED BY MODULATION OF DEFENSE, PHYTOHORMONE, STRESS-RESPONSE, AND CIRCADIAN RHYTHM GENES, AS WELL AS HERITABLE CHANGES IN DNA METHYLATION PATTERNS. CONSISTENT WITH GENE EXPRESSION CHANGES, MSH1 MUTANTS DISPLAY ENHANCED TOLERANCE FOR ABIOTIC STRESS INCLUDING DROUGHT AND SALT STRESS, WHILE SHOWING INCREASED SUSCEPTIBILITY TO FREEZING TEMPERATURES. DESPITE CHANGES IN DEFENSE AND BIOTIC STRESS-RESPONSE GENES, MSH1 MUTANTS SHOWED INCREASING SUSCEPTIBILITY TO THE BACTERIAL PATHOGEN PSEUDOMONAS SYRINGAE. OUR RESULTS SUGGEST THAT CHRONIC COLD AND LOW LIGHT STRESS (10 DEGREES C, 150 MUMOL M(-2) S(-1)) INFLUENCES NON-CG METHYLATION TO A GREATER DEGREE IN MSH1 MUTANTS COMPARED TO WILD-TYPE COL-0. FURTHERMORE, CHG CHANGES ARE MORE CLOSELY PERICENTROMERIC, WHEREAS CHH CHANGES ARE GENERALLY MORE DISPERSED. THIS INCREASED VARIATION IN NON-CG METHYLATION PATTERN DOES NOT SIGNIFICANTLY AFFECT THE MSH1-DERIVED ENHANCED GROWTH BEHAVIOR AFTER MUTANTS ARE CROSSED WITH ISOGENIC WILD TYPE, REITERATING THE IMPORTANCE OF CG METHYLATION CHANGES IN MSH1-DERIVED ENHANCED VIGOR. THESE RESULTS INDICATE THAT MSH1METHYLOME IS HYPER-RESPONSIVE TO ENVIRONMENTAL STRESS IN A MANNER DISTINCT FROM THE WILD-TYPE RESPONSE, BUT CG METHYLATION CHANGES ARE POTENTIALLY RESPONSIBLE FOR GROWTH VIGOR CHANGES IN THE CROSSED PROGENY. 2018 5 1184 40 COOPERATIVE EPIGENETIC REMODELING BY TET2 LOSS AND NRAS MUTATION DRIVES MYELOID TRANSFORMATION AND MEK INHIBITOR SENSITIVITY. MUTATIONS IN EPIGENETIC MODIFIERS AND SIGNALING FACTORS OFTEN CO-OCCUR IN MYELOID MALIGNANCIES, INCLUDING TET2 AND NRAS MUTATIONS. CONCURRENT TET2 LOSS AND NRAS(G12D) EXPRESSION IN HEMATOPOIETIC CELLS INDUCED MYELOID TRANSFORMATION, WITH A FULLY PENETRANT, LETHAL CHRONIC MYELOMONOCYTIC LEUKEMIA (CMML), WHICH WAS SERIALLY TRANSPLANTABLE. TET2 LOSS AND NRAS MUTATION COOPERATIVELY LED TO DECREASE IN NEGATIVE REGULATORS OF MITOGEN-ACTIVATED PROTEIN KINASE (MAPK) ACTIVATION, INCLUDING SPRY2, THEREBY CAUSING SYNERGISTIC ACTIVATION OF MAPK SIGNALING BY EPIGENETIC SILENCING. TET2/NRAS DOUBLE-MUTANT LEUKEMIA SHOWED PREFERENTIAL SENSITIVITY TO MAPK KINASE (MEK) INHIBITION IN BOTH MOUSE MODEL AND PATIENT SAMPLES. THESE DATA PROVIDE INSIGHTS INTO HOW EPIGENETIC AND SIGNALING MUTATIONS COOPERATE IN MYELOID TRANSFORMATION AND PROVIDE A RATIONALE FOR MECHANISM-BASED THERAPY IN CMML PATIENTS WITH THESE HIGH-RISK GENETIC LESIONS. 2018 6 6383 35 THE ROLE OF PHF6 IN HEMATOPOIESIS AND HEMATOLOGIC MALIGNANCIES. EPIGENETIC REGULATION OF GENE EXPRESSION REPRESENTS AN IMPORTANT MECHANISM IN THE MAINTENANCE OF STEM CELL FUNCTION. ALTERATIONS IN EPIGENETIC REGULATION CONTRIBUTE TO THE PATHOGENESIS OF HEMATOLOGICAL MALIGNANCIES. PLANT HOMEODOMAIN FINGER PROTEIN 6 (PHF6) IS A MEMBER OF THE PLANT HOMEODOMAIN (PHD)-LIKE ZINC FINGER FAMILY OF PROTEINS THAT IS INVOLVED IN TRANSCRIPTIONAL REGULATION THROUGH THE MODIFICATION OF THE CHROMATIN STATE. GERMLINE MUTATION OF PHF6 IS THE CAUSATIVE GENETIC ALTERATION OF THE X-LINKED MENTAL RETARDATION BORJESON-FORSSMAN-LEHMANN SYNDROME (BFLS). SOMATIC MUTATIONS IN PHF6 ARE IDENTIFIED IN HUMAN LEUKEMIA, SUCH AS ADULT T-CELL ACUTE LYMPHOBLASTIC LEUKEMIA (T-ALL, ~ 38%), PEDIATRIC T-ALL (~ 16%), ACUTE MYELOID LEUKEMIA (AML, ~ 3%), CHRONIC MYELOID LEUKEMIA (CML, ~ 2.5%), MIXED PHENOTYPE ACUTE LEUKEMIA (MPAL, ~ 20%), AND HIGH-GRADE B-CELL LYMPHOMA (HGBCL, ~ 3%). MORE RECENT STUDIES IMPLY AN ONCOGENIC EFFECT OF PHF6 IN B-CELL ACUTE LYMPHOBLASTIC LEUKEMIA (B-ALL) AND SOLID TUMORS. THESE DATA DEMONSTRATE THAT PHF6 COULD ACT AS A DOUBLE-EDGED SWORD, EITHER A TUMOR SUPPRESSOR OR AN ONCOGENE, IN A LINEAGE-DEPENDENT MANNER. HOWEVER, THE UNDERLYING MECHANISMS OF PHF6 IN NORMAL HEMATOPOIESIS AND LEUKEMOGENESIS REMAIN LARGELY UNKNOWN. IN THIS REVIEW, WE SUMMARIZE CURRENT KNOWLEDGE OF PHF6, EMPHASIZING THE ROLE OF PHF6 IN HEMATOLOGICAL MALIGNANCIES. EPIGENETIC REGULATION OF PHF6 IN B-ALL. PHF6 MAINTAINS A CHROMATIN STRUCTURE THAT IS PERMISSIVE TO B-CELL IDENTITY GENES, BUT NOT T-CELL-SPECIFIC GENES (LEFT). LOSS OF PHF6 LEADS TO ABERRANT EXPRESSION OF B-CELL- AND T-CELL-SPECIFIC GENES RESULTING FROM LINEAGE PROMISCUITY AND BINDING OF T-CELL TRANSCRIPTION FACTORS (RIGHT). 2023 7 6037 21 THE CHD6 CHROMATIN REMODELER IS AN OXIDATIVE DNA DAMAGE RESPONSE FACTOR. CELL SURVIVAL AFTER OXIDATIVE DNA DAMAGE REQUIRES SIGNALING, REPAIR AND TRANSCRIPTIONAL EVENTS OFTEN ENABLED BY NUCLEOSOME DISPLACEMENT, EXCHANGE OR REMOVAL BY CHROMATIN REMODELING ENZYMES. HERE, WE SHOW THAT CHROMODOMAIN HELICASE DNA-BINDING PROTEIN 6 (CHD6), DISTINCT TO OTHER CHD ENZYMES, IS STABILIZED DURING OXIDATIVE STRESS VIA REDUCED DEGRADATION. CHD6 RELOCATES RAPIDLY TO DNA DAMAGE IN A MANNER DEPENDENT UPON OXIDATIVE LESIONS AND A CONSERVED N-TERMINAL POLY(ADP-RIBOSE)-DEPENDENT RECRUITMENT MOTIF, WITH LATER RETENTION REQUIRING THE DOUBLE CHROMODOMAIN AND CENTRAL CORE. CHD6 ABLATION INCREASES REACTIVE OXYGEN SPECIES PERSISTENCE AND IMPAIRS ANTI-OXIDANT TRANSCRIPTIONAL RESPONSES, LEADING TO ELEVATED DNA BREAKAGE AND POLY(ADP-RIBOSE) INDUCTION THAT CANNOT BE RESCUED BY CATALYTIC OR DOUBLE CHROMODOMAIN MUTANTS. DESPITE NO OVERT EPIGENETIC OR DNA REPAIR ABNORMALITIES, CHD6 LOSS LEADS TO IMPAIRED CELL SURVIVAL AFTER CHRONIC OXIDATIVE STRESS, ABNORMAL CHROMATIN RELAXATION, AMPLIFIED DNA DAMAGE SIGNALING AND CHECKPOINT HYPERSENSITIVITY. WE SUGGEST THAT CHD6 IS A KEY REGULATOR OF THE OXIDATIVE DNA DAMAGE RESPONSE. 2019 8 5965 41 TEN-ELEVEN-TRANSLOCATION 2 (TET2) NEGATIVELY REGULATES HOMEOSTASIS AND DIFFERENTIATION OF HEMATOPOIETIC STEM CELLS IN MICE. THE TEN-ELEVEN-TRANSLOCATION 2 (TET2) GENE ENCODES A MEMBER OF TET FAMILY ENZYMES THAT ALTERS THE EPIGENETIC STATUS OF DNA BY OXIDIZING 5-METHYLCYTOSINE TO 5-HYDROXYMETHYLCYTOSINE (5HMC). SOMATIC LOSS-OF-FUNCTION MUTATIONS OF TET2 ARE FREQUENTLY OBSERVED IN PATIENTS WITH DIVERSE MYELOID MALIGNANCIES, INCLUDING MYELODYSPLASTIC SYNDROMES, MYELOPROLIFERATIVE NEOPLASMS, AND CHRONIC MYELOMONOCYTIC LEUKEMIA. BY ANALYZING MICE WITH TARGETED DISRUPTION OF THE TET2 CATALYTIC DOMAIN, WE SHOW HERE THAT TET2 IS A CRITICAL REGULATOR OF SELF-RENEWAL AND DIFFERENTIATION OF HEMATOPOIETIC STEM CELLS (HSCS). TET2 DEFICIENCY LED TO DECREASED GENOMIC LEVELS OF 5HMC AND AUGMENTED THE SIZE OF THE HEMATOPOIETIC STEM/PROGENITOR CELL POOL IN A CELL-AUTONOMOUS MANNER. IN COMPETITIVE TRANSPLANTATION ASSAYS, TET2-DEFICIENT HSCS WERE CAPABLE OF MULTILINEAGE RECONSTITUTION AND POSSESSED A COMPETITIVE ADVANTAGE OVER WILD-TYPE HSCS, RESULTING IN ENHANCED HEMATOPOIESIS INTO BOTH LYMPHOID AND MYELOID LINEAGES. IN VITRO, TET2 DEFICIENCY DELAYED HSC DIFFERENTIATION AND SKEWED DEVELOPMENT TOWARD THE MONOCYTE/MACROPHAGE LINEAGE. OUR DATA INDICATE THAT TET2 HAS A CRITICAL ROLE IN REGULATING THE EXPANSION AND FUNCTION OF HSCS, PRESUMABLY BY CONTROLLING 5HMC LEVELS AT GENES IMPORTANT FOR THE SELF-RENEWAL, PROLIFERATION, AND DIFFERENTIATION OF HSCS. 2011 9 5333 21 PYRUVATE KINASE DEFICIENCY: THE GENOTYPE-PHENOTYPE ASSOCIATION. RED CELL PYRUVATE KINASE (PK) DEFICIENCY IS THE MOST FREQUENT ENZYME ABNORMALITY OF GLYCOLYSIS CAUSING CHRONIC NON-SPHEROCYTIC HAEMOLYTIC ANAEMIA. THE DISEASE IS TRANSMITTED AS AN AUTOSOMAL RECESSIVE TRAIT, CLINICAL SYMPTOMS USUALLY OCCURRING IN COMPOUND HETEROZYGOTES FOR TWO MUTANT ALLELES AND IN HOMOZYGOTES. THE SEVERITY OF HAEMOLYSIS IS HIGHLY VARIABLE, RANGING FROM VERY MILD OR FULLY COMPENSATED FORMS TO LIFE-THREATENING NEONATAL ANAEMIA NECESSITATING EXCHANGE TRANSFUSIONS. ERYTHROCYTE PK IS SYNTHESISED UNDER THE CONTROL OF THE PK-LR GENE LOCATED ON CHROMOSOME 1. ONE HUNDRED EIGHTY DIFFERENT MUTATIONS IN PK-LR GENE, MOSTLY MISSENSE, HAVE BEEN SO FAR REPORTED ASSOCIATED TO PK DEFICIENCY. FIRST ATTEMPTS TO DELINEATE THE GENOTYPE-PHENOTYPE ASSOCIATION WERE MAINLY BASED ON THE ANALYSIS OF THE ENZYME'S THREE-DIMENSIONAL STRUCTURE AND THE OBSERVATION OF THE FEW HOMOZYGOUS PATIENTS. MORE RECENTLY, THE COMPARISON OF THE RECOMBINANT MUTANTS OF HUMAN RED CELL PK WITH THE WILD-TYPE ENZYME HAS ENABLED THE EFFECTS OF AMINO ACID REPLACEMENTS ON THE ENZYME MOLECULAR PROPERTIES TO BE DETERMINED. HOWEVER, THE CLINICAL MANIFESTATIONS OF RED CELL ENZYME DEFECTS ARE NOT MERELY DEPENDENT ON THE MOLECULAR PROPERTIES OF THE MUTANT PROTEIN BUT RATHER REFLECT THE COMPLEX INTERACTIONS OF ADDITIONAL FACTORS, INCLUDING GENETIC BACKGROUND, CONCOMITANT FUNCTIONAL POLYMORPHISMS OF OTHER ENZYMES, POSTTRANSLATIONAL OR EPIGENETIC MODIFICATIONS, INEFFECTIVE ERYTHROPOIESIS AND DIFFERENCES IN SPLENIC FUNCTION. 2007 10 5953 30 TARGETS IN MPNS AND POTENTIAL THERAPEUTICS. PHILADELPHIA-NEGATIVE CLASSICAL MYELOPROLIFERATIVE NEOPLASMS (MPNS), INCLUDING POLYCYTHEMIA VERA (PV), ESSENTIAL THROMBOCYTHEMIA (ET) AND PRIMARY MYELOFIBROSIS (PMF), ARE CLONAL HEMOPATHIES THAT EMERGE IN THE HEMATOPOIETIC STEM CELL (HSC) COMPARTMENT. MPN DRIVER MUTATIONS ARE RESTRICTED TO SPECIFIC EXONS (14 AND 12) OF JANUS KINASE 2 (JAK2), THROMBOPOIETIN RECEPTOR (MPL/TPOR) AND CALRETICULIN (CALR) GENES, ARE INVOLVED DIRECTLY IN CLONAL MYELOPROLIFERATION AND GENERATE THE MPN PHENOTYPE. AS A RESULT, AN INCREASED NUMBER OF FULLY FUNCTIONAL ERYTHROCYTES, PLATELETS AND LEUKOCYTES IS OBSERVED IN THE PERIPHERAL BLOOD. NEVERTHELESS, THE COMPLEXITY AND HETEROGENEITY OF MPN CLINICAL PHENOTYPES CANNOT BE SOLELY EXPLAINED BY THE TYPE OF DRIVER MUTATION. OTHER FACTORS, SUCH AS ADDITIONAL SOMATIC MUTATIONS AFFECTING EPIGENETIC REGULATORS OR SPLICEOSOMES COMPONENTS, MUTANT ALLELE BURDENS AND MODIFIERS OF SIGNALING BY DRIVER MUTANTS, CLONAL ARCHITECTURE AND THE ORDER OF MUTATION ACQUISITION, SIGNALING EVENTS THAT OCCUR DOWNSTREAM OF A DRIVER MUTATION, THE PRESENCE OF SPECIFIC GERM-LINE VARIANTS, THE INTERACTION OF THE NEOPLASTIC CLONE WITH BONE MARROW MICROENVIRONMENT AND CHRONIC INFLAMMATION, ALL CAN MODULATE THE DISEASE PHENOTYPE, INFLUENCE THE MPN CLINICAL COURSE AND THEREFORE, MIGHT BE USEFUL THERAPEUTIC TARGETS. 2022 11 535 36 ASXL1 MUTATION CORRECTION BY CRISPR/CAS9 RESTORES GENE FUNCTION IN LEUKEMIA CELLS AND INCREASES SURVIVAL IN MOUSE XENOGRAFTS. RECURRENT SOMATIC MUTATIONS OF THE EPIGENETIC MODIFIER AND TUMOR SUPPRESSOR ASXL1 ARE COMMON IN MYELOID MALIGNANCIES, INCLUDING CHRONIC MYELOID LEUKEMIA (CML), AND ARE ASSOCIATED WITH POOR CLINICAL OUTCOME. CRISPR/CAS9 HAS RECENTLY EMERGED AS A POWERFUL AND VERSATILE GENOME EDITING TOOL FOR GENOME ENGINEERING IN VARIOUS SPECIES. WE HAVE USED THE CRISPR/CAS9 SYSTEM TO CORRECT THE ASXL1 HOMOZYGOUS NONSENSE MUTATION PRESENT IN THE CML CELL LINE KBM5, WHICH LACKS ASXL1 PROTEIN EXPRESSION. CRISPR/CAS9-MEDIATED ASXL1 HOMOZYGOUS CORRECTION RESULTED IN PROTEIN RE-EXPRESSION WITH RESTORED NORMAL FUNCTION, INCLUDING DOWN-REGULATION OF POLYCOMB REPRESSIVE COMPLEX 2 TARGET GENES. SIGNIFICANTLY REDUCED CELL GROWTH AND INCREASED MYELOID DIFFERENTIATION WERE OBSERVED IN ASXL1 MUTATION-CORRECTED CELLS, PROVIDING NEW INSIGHTS INTO THE ROLE OF ASXL1 IN HUMAN MYELOID CELL DIFFERENTIATION. MICE XENOGRAFTED WITH MUTATION-CORRECTED KBM5 CELLS SHOWED SIGNIFICANTLY LONGER SURVIVAL THAN UNCORRECTED XENOGRAFTS. THESE RESULTS SHOW THAT THE SOLE CORRECTION OF A DRIVER MUTATION IN LEUKEMIA CELLS INCREASES SURVIVAL IN VIVO IN MICE. THIS STUDY PROVIDES PROOF-OF-CONCEPT FOR DRIVER GENE MUTATION CORRECTION VIA CRISPR/CAS9 TECHNOLOGY IN HUMAN LEUKEMIA CELLS AND PRESENTS A STRATEGY TO ILLUMINATE THE IMPACT OF ONCOGENIC MUTATIONS ON CELLULAR FUNCTION AND SURVIVAL. 2015 12 3878 36 KDM6B OVEREXPRESSION ACTIVATES INNATE IMMUNE SIGNALING AND IMPAIRS HEMATOPOIESIS IN MICE. KDM6B IS AN EPIGENETIC REGULATOR THAT MEDIATES TRANSCRIPTIONAL ACTIVATION DURING DIFFERENTIATION, INCLUDING IN BONE MARROW (BM) HEMATOPOIETIC STEM AND PROGENITOR CELLS (HSPCS). OVEREXPRESSION OF KDM6B HAS BEEN REPORTED IN BM HSPCS OF PATIENTS WITH MYELODYSPLASTIC SYNDROMES (MDS) AND CHRONIC MYELOMONOCYTIC LEUKEMIA (CMML). WHETHER THE OVEREXPRESSION OF KDM6B CONTRIBUTES TO THE PATHOGENESIS OF THESE DISEASES REMAINS TO BE ELUCIDATED. TO STUDY THIS, WE GENERATED A VAV-KDM6B MOUSE MODEL, WHICH OVEREXPRESSES KDM6B IN THE HEMATOPOIETIC COMPARTMENT. KDM6B OVEREXPRESSION ALONE LED TO MILD HEMATOPOIETIC PHENOTYPE, AND CHRONIC INNATE IMMUNE STIMULATION OF VAV-KDM6B MICE WITH THE TOLL-LIKE RECEPTOR (TLR) LIGAND LIPOPOLYSACCHARIDE (LPS) RESULTED IN SIGNIFICANT HEMATOPOIETIC DEFECTS. THESE DEFECTS RECAPITULATED FEATURES OF MDS AND CMML, INCLUDING LEUKOPENIA, DYSPLASIA, AND COMPROMISED REPOPULATING FUNCTION OF BM HSPCS. TRANSCRIPTOME STUDIES INDICATED THAT KDM6B OVEREXPRESSION ALONE COULD LEAD TO ACTIVATION OF DISEASE-RELEVANT GENES SUCH AS S100A9 IN BM HSPCS, AND WHEN COMBINED WITH INNATE IMMUNE STIMULATION, KDM6B OVEREXPRESSION RESULTED IN MORE PROFOUND OVEREXPRESSION OF INNATE IMMUNE AND DISEASE-RELEVANT GENES, INDICATING THAT KDM6B WAS INVOLVED IN THE ACTIVATION OF INNATE IMMUNE SIGNALING IN BM HSPCS. FINALLY, PHARMACOLOGIC INHIBITION OF KDM6B WITH THE SMALL MOLECULE INHIBITOR GSK-J4 AMELIORATED THE INEFFECTIVE HEMATOPOIESIS OBSERVED IN VAV-KDM6B MICE. THIS EFFECT WAS ALSO OBSERVED WHEN GSK-J4 WAS APPLIED TO THE PRIMARY BM HSPCS OF PATIENTS WITH MDS BY IMPROVING THEIR REPOPULATING FUNCTION. THESE RESULTS INDICATE THAT OVEREXPRESSION OF KDM6B MEDIATES ACTIVATION OF INNATE IMMUNE SIGNALS AND HAS A ROLE IN MDS AND CMML PATHOGENESIS, AND THAT KDM6B TARGETING HAS THERAPEUTIC POTENTIAL IN THESE MYELOID DISORDERS. 2018 13 4739 24 NOVEL GENE-SPECIFIC TRANSLATION MECHANISM OF DYSREGULATED, CHRONIC INFLAMMATION REVEALS PROMISING, MULTIFACETED COVID-19 THERAPEUTICS. HYPERINFLAMMATION AND LYMPHOPENIA PROVOKED BY SARS-COV-2-ACTIVATED MACROPHAGES CONTRIBUTE TO THE HIGH MORTALITY OF CORONAVIRUS DISEASE 2019 (COVID-19) PATIENTS. THUS, DEFINING HOST PATHWAYS ABERRANTLY ACTIVATED IN PATIENT MACROPHAGES IS CRITICAL FOR DEVELOPING EFFECTIVE THERAPEUTICS. WE DISCOVERED THAT G9A, A HISTONE METHYLTRANSFERASE THAT IS OVEREXPRESSED IN COVID-19 PATIENTS WITH HIGH VIRAL LOAD, ACTIVATES TRANSLATION OF SPECIFIC GENES THAT INDUCE HYPERINFLAMMATION AND IMPAIRMENT OF T CELL FUNCTION OR LYMPHOPENIA. THIS NONCANONICAL, PRO-TRANSLATION ACTIVITY OF G9A CONTRASTS WITH ITS CANONICAL EPIGENETIC FUNCTION. IN ENDOTOXIN-TOLERANT (ET) MACROPHAGES THAT MIMIC CONDITIONS WHICH RENDER PATIENTS WITH PRE-EXISTING CHRONIC INFLAMMATORY DISEASES VULNERABLE TO SEVERE SYMPTOMS, OUR CHEMOPROTEOMIC APPROACH WITH A BIOTINYLATED INHIBITOR OF G9A IDENTIFIED MULTIPLE G9A-ASSOCIATED TRANSLATION REGULATORY PATHWAYS THAT WERE UPREGULATED BY SARS-COV-2 INFECTION. FURTHER, QUANTITATIVE TRANSLATOME ANALYSIS OF ET MACROPHAGES TREATED PROGRESSIVELY WITH THE G9A INHIBITOR PROFILED G9A-TRANSLATED PROTEINS THAT UNITE THE NETWORKS ASSOCIATED WITH VIRAL REPLICATION AND THE SARS-COV-2-INDUCED HOST RESPONSE IN SEVERE PATIENTS. ACCORDINGLY, INHIBITION OF G9A-ASSOCIATED PATHWAYS PRODUCED MULTIFACETED, SYSTEMATIC EFFECTS, NAMELY, RESTORATION OF T CELL FUNCTION, MITIGATION OF HYPERINFLAMMATION, AND SUPPRESSION OF VIRAL REPLICATION. IMPORTANTLY, AS A HOST-DIRECTED MECHANISM, THIS G9A-TARGETED, COMBINED THERAPEUTICS IS REFRACTORY TO EMERGING ANTIVIRAL-RESISTANT MUTANTS OF SARS-COV-2, OR ANY VIRUS, THAT HIJACKS HOST RESPONSES. 2020 14 5405 36 REGULATED EXPRESSION OF P210 BCR-ABL DURING EMBRYONIC STEM CELL DIFFERENTIATION STIMULATES MULTIPOTENTIAL PROGENITOR EXPANSION AND MYELOID CELL FATE. P210 BCR-ABL IS AN ACTIVATED TYROSINE KINASE ONCOGENE ENCODED BY THE PHILADELPHIA CHROMOSOME ASSOCIATED WITH HUMAN CHRONIC MYELOGENOUS LEUKEMIA (CML). THE DISEASE REPRESENTS A CLONAL DISORDER ARISING IN THE PLURIPOTENT HEMATOPOIETIC STEM CELL. DURING THE CHRONIC PHASE, PATIENTS PRESENT WITH A DRAMATIC EXPANSION OF MYELOID CELLS AND A MILD ANEMIA. RETROVIRAL GENE TRANSFER AND TRANSGENIC EXPRESSION IN RODENTS HAVE DEMONSTRATED THE ABILITY OF BCR-ABL TO INDUCE VARIOUS TYPES OF LEUKEMIA. HOWEVER, STUDY OF HUMAN CML OR RODENT MODELS HAS NOT DETERMINED THE DIRECT AND IMMEDIATE EFFECTS OF BCR-ABL ON HEMATOPOIETIC CELLS FROM THOSE REQUIRING SECONDARY GENETIC OR EPIGENETIC CHANGES SELECTED DURING THE PATHOGENIC PROCESS. WE UTILIZED TETRACYCLINE-REGULATED EXPRESSION OF BCR-ABL FROM A PROMOTER ENGINEERED FOR ROBUST EXPRESSION IN PRIMITIVE STEM CELLS THROUGH MULTILINEAGE BLOOD CELL DEVELOPMENT IN COMBINATION WITH THE IN VITRO DIFFERENTIATION OF EMBRYONAL STEM CELLS INTO HEMATOPOIETIC ELEMENTS. OUR RESULTS DEMONSTRATE THAT BCR-ABL EXPRESSION ALONE IS SUFFICIENT TO INCREASE THE NUMBER OF MULTIPOTENT AND MYELOID LINEAGE COMMITTED PROGENITORS IN A DOSE-DEPENDENT MANNER WHILE SUPPRESSING THE DEVELOPMENT OF COMMITTED ERYTHROID PROGENITORS. THESE EFFECTS ARE REVERSIBLE UPON EXTINGUISHING BCR-ABL EXPRESSION. THESE FINDINGS ARE CONSISTENT WITH BCR-ABL BEING THE SOLE GENETIC CHANGE NEEDED FOR THE ESTABLISHMENT OF THE CHRONIC PHASE OF CML AND PROVIDE A POWERFUL SYSTEM FOR THE ANALYSIS OF ANY GENETIC CHANGE THAT ALTERS CELL GROWTH AND LINEAGE CHOICES OF THE HEMATOPOIETIC STEM CELL. 2000 15 3357 24 HISTONE H3 LYSINE 9 DI-METHYLATION AS AN EPIGENETIC SIGNATURE OF THE INTERFERON RESPONSE. EFFECTIVE ANTIVIRAL IMMUNITY DEPENDS ON THE ABILITY OF INFECTED CELLS OR CELLS TRIGGERED WITH VIRUS-DERIVED NUCLEIC ACIDS TO PRODUCE TYPE I INTERFERON (IFN), WHICH ACTIVATES TRANSCRIPTION OF NUMEROUS ANTIVIRAL GENES. HOWEVER, DISPROPORTIONATELY STRONG OR CHRONIC IFN EXPRESSION IS A COMMON CAUSE OF INFLAMMATORY AND AUTOIMMUNE DISEASES. WE DESCRIBE AN EPIGENETIC MECHANISM THAT DETERMINES CELL TYPE-SPECIFIC DIFFERENCES IN IFN AND IFN-STIMULATED GENE (ISG) EXPRESSION IN RESPONSE TO EXOGENOUS SIGNALS. WE IDENTIFY DI-METHYLATION OF HISTONE H3 AT LYSINE 9 (H3K9ME2) AS A SUPPRESSOR OF IFN AND IFN-INDUCIBLE ANTIVIRAL GENE EXPRESSION. WE SHOW THAT LEVELS OF H3K9ME2 AT IFN AND ISG CORRELATE INVERSELY WITH THE SCOPE AND AMPLITUDE OF IFN AND ISG EXPRESSION IN FIBROBLASTS AND DENDRITIC CELLS. ACCORDINGLY, GENETIC ABLATION OR PHARMACOLOGICAL INACTIVATION OF LYSINE METHYLTRANSFERASE G9A, WHICH IS ESSENTIAL FOR THE GENERATION OF H3K9ME2, RESULTED IN PHENOTYPIC CONVERSION OF FIBROBLASTS INTO HIGHLY POTENT IFN-PRODUCING CELLS AND RENDERED THESE CELLS RESISTANT TO PATHOGENIC RNA VIRUSES. IN SUMMARY, OUR STUDIES IMPLICATE H3K9ME2 AND ENZYMES CONTROLLING ITS ABUNDANCE AS KEY REGULATORS OF INNATE ANTIVIRAL IMMUNITY. 2012 16 2278 32 EPIGENETIC REGULATION BY SUV4-20H1 IN CARDIOPULMONARY PROGENITOR CELLS IS REQUIRED TO PREVENT PULMONARY HYPERTENSION AND CHRONIC OBSTRUCTIVE PULMONARY DISEASE. BACKGROUND: THE PATHOGENESIS OF LIFE-THREATENING CARDIOPULMONARY DISEASES SUCH AS PULMONARY HYPERTENSION (PH) AND CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD) ORIGINATES FROM A COMPLEX INTERPLAY OF ENVIRONMENTAL FACTORS AND GENETIC PREDISPOSITIONS THAT IS NOT FULLY UNDERSTOOD. LIKEWISE, LITTLE IS KNOWN ABOUT DEVELOPMENTAL ABNORMALITIES OR EPIGENETIC DYSREGULATIONS THAT MIGHT PREDISPOSE FOR PH OR COPD IN ADULT INDIVIDUALS. METHODS: TO IDENTIFY PATHOLOGY-ASSOCIATED EPIGENETIC ALTERATION IN DISEASED LUNG TISSUES, WE SCREENED A COHORT OF HUMAN PATIENTS WITH PH AND COPD FOR CHANGES OF HISTONE MODIFICATIONS BY IMMUNOFLUORESCENCE STAINING. TO ANALYZE THE FUNCTION OF H4K20ME2/3 IN LUNG PATHOGENESIS, WE DEVELOPED A SERIES OF SUV4-20H1 KNOCKOUT MOUSE LINES TARGETING CARDIOPULMONARY PROGENITOR CELLS AND DIFFERENT HEART AND LUNG CELL TYPES, FOLLOWED BY HEMODYNAMIC STUDIES AND MORPHOMETRIC ASSESSMENT OF TISSUE SAMPLES. MOLECULAR, CELLULAR, AND BIOCHEMICAL TECHNIQUES WERE APPLIED TO ANALYZE THE FUNCTION OF SUV4-20H1-DEPENDENT EPIGENETIC PROCESSES IN CARDIOPULMONARY PROGENITOR CELLS AND THEIR DERIVATIVES. RESULTS: WE DISCOVERED A STRONG REDUCTION OF THE HISTONE MODIFICATIONS OF H4K20ME2/3 IN HUMAN PATIENTS WITH COPD BUT NOT PATIENTS WITH PH THAT DEPEND ON THE ACTIVITY OF THE H4K20 DI-METHYLTRANSFERASE SUV4-20H1. LOSS OF SUV4-20H1 IN CARDIOPULMONARY PROGENITOR CELLS CAUSED A COPD-LIKE/PH PHENOTYPE IN MICE INCLUDING THE FORMATION OF PERIVASCULAR TERTIARY LYMPHOID TISSUE AND GOBLET CELL HYPERPLASIA, HYPERPROLIFERATION OF SMOOTH MUSCLE CELLS/MYOFIBROBLASTS, IMPAIRED ALVEOLARIZATION AND MATURATION DEFECTS OF THE MICROVASCULATURE LEADING TO MASSIVE RIGHT VENTRICULAR DILATATION AND PREMATURE DEATH. MECHANISTICALLY, SUV4-20H1 BINDS DIRECTLY TO THE 5'-UPSTREAM REGULATORY ELEMENT OF THE SUPEROXIDE DISMUTASE 3 (SOD3) GENE TO REPRESS ITS EXPRESSION. INCREASED LEVELS OF THE EXTRACELLULAR SOD3 ENZYME IN SUV4-20H1 MUTANTS INCREASES HYDROGEN PEROXIDE CONCENTRATIONS, CAUSING VASCULAR DEFECTS AND IMPAIRING ALVEOLARIZATION. CONCLUSIONS: OUR FINDINGS REVEAL A PIVOTAL ROLE OF THE HISTONE MODIFIER SUV4-20H1 IN CARDIOPULMONARY CODEVELOPMENT AND UNCOVER THE DEVELOPMENTAL ORIGINS OF CARDIOPULMONARY DISEASES. WE ASSUME THAT THE STUDY WILL FACILITATE THE UNDERSTANDING OF PATHOGENIC EVENTS CAUSING PH AND COPD AND AID THE DEVELOPMENT OF EPIGENETIC DRUGS FOR THE TREATMENT OF CARDIOPULMONARY DISEASES. 2021 17 1674 33 DRIVER MUTATIONS IN LEUKEMIA PROMOTE DISEASE PATHOGENESIS THROUGH A COMBINATION OF CELL-AUTONOMOUS AND NICHE MODULATION. STUDIES OF PATIENTS WITH ACUTE MYELOID LEUKEMIA (AML) HAVE LED TO THE IDENTIFICATION OF MUTATIONS THAT AFFECT DIFFERENT CELLULAR PATHWAYS. SOME OF THESE HAVE BEEN CLASSIFIED AS PRELEUKEMIC, AND A STEPWISE EVOLUTION PROGRAM WHEREBY CELLS ACQUIRE ADDITIONAL MUTATIONS HAS BEEN PROPOSED IN THE DEVELOPMENT OF AML. HOW THE TIMING OF ACQUISITION OF THESE MUTATIONS AND THEIR IMPACT ON TRANSFORMATION AND THE BONE MARROW (BM) MICROENVIRONMENT OCCURS HAS ONLY RECENTLY BEGUN TO BE INVESTIGATED. WE SHOW THAT CONSTITUTIVE AND EARLY LOSS OF THE EPIGENETIC REGULATOR, TET2, WHEN COMBINED WITH CONSTITUTIVE ACTIVATION OF FLT3, RESULTS IN TRANSFORMATION OF CHRONIC MYELOMONOCYTIC LEUKEMIA-LIKE OR MYELOPROLIFERATIVE NEOPLASM-LIKE PHENOTYPE TO AML, WHICH IS MORE PRONOUNCED IN DOUBLE-MUTANT MICE RELATIVE TO MICE CARRYING MUTATIONS IN SINGLE GENES. FURTHERMORE, WE SHOW THAT IN PRELEUKEMIC AND LEUKEMIC MICE THERE ARE ALTERATIONS IN THE BM NICHE AND SECRETED CYTOKINES, WHICH CREATES A PERMISSIVE ENVIRONMENT FOR THE GROWTH OF MUTATION-BEARING CELLS RELATIVE TO NORMAL CELLS. 2020 18 3362 30 HISTONE LYSINE DEMETHYLASE KDM5B MAINTAINS CHRONIC MYELOID LEUKEMIA VIA MULTIPLE EPIGENETIC ACTIONS. THE HISTONE LYSINE DEMETHYLASE KDM5 FAMILY IS IMPLICATED IN NORMAL DEVELOPMENT AND STEM CELL MAINTENANCE BY EPIGENETIC MODULATION OF HISTONE METHYLATION STATUS. DEREGULATION OF THE KDM5 FAMILY HAS BEEN REPORTED IN VARIOUS TYPES OF CANCERS, INCLUDING HEMATOLOGICAL MALIGNANCIES. HOWEVER, THEIR TRANSCRIPTIONAL REGULATORY ROLES IN THE CONTEXT OF LEUKEMIA REMAIN UNCLEAR. HERE, WE FIND THAT KDM5B IS STRONGLY EXPRESSED IN NORMAL CD34(+) HEMATOPOIETIC STEM/PROGENITOR CELLS AND CHRONIC MYELOID LEUKEMIA (CML) CELLS. KNOCKDOWN OF KDM5B IN K562 CML CELLS REDUCED LEUKEMIA COLONY-FORMING POTENTIAL. TRANSCRIPTOME PROFILING OF KDM5B KNOCKDOWN K562 CELLS REVEALED THE DEREGULATION OF GENES INVOLVED IN MYELOID DIFFERENTIATION AND TOLL-LIKE RECEPTOR SIGNALING. THROUGH THE INTEGRATION OF TRANSCRIPTOME AND CHIP-SEQ PROFILING DATA, WE SHOW THAT KDM5B IS ENRICHED AT THE BINDING SITES OF THE GATA AND AP-1 TRANSCRIPTION FACTOR FAMILIES, SUGGESTING THEIR COLLABORATIONS IN THE REGULATION OF TRANSCRIPTION. EVEN THOUGH THE BINDING OF KDM5B SUBSTANTIALLY OVERLAPPED WITH H3K4ME1 OR H3K4ME3 MARK AT GENE PROMOTERS, ONLY A SMALL SUBSET OF THE KDM5B TARGETS SHOWED DIFFERENTIAL EXPRESSION IN ASSOCIATION WITH THE HISTONE DEMETHYLATION ACTIVITY. BY CHARACTERIZING THE INTERACTING PROTEINS IN K562 CELLS, WE DISCOVERED THAT KDM5B RECRUITS PROTEIN COMPLEXES INVOLVED IN THE MRNA PROCESSING MACHINERY, IMPLYING AN ALTERNATIVE EPIGENETIC ACTION MEDIATED BY KDM5B IN GENE REGULATION. OUR STUDY HIGHLIGHTS THE ONCOGENIC FUNCTIONS OF KDM5B IN CML CELLS AND SUGGESTS THAT KDM5B IS VITAL TO THE TRANSCRIPTIONAL REGULATION VIA MULTIPLE EPIGENETIC MECHANISMS. 2020 19 923 30 CHRONIC INFECTION DRIVES DNMT3A-LOSS-OF-FUNCTION CLONAL HEMATOPOIESIS VIA IFNGAMMA SIGNALING. AGE-RELATED CLONAL HEMATOPOIESIS (CH) IS A RISK FACTOR FOR MALIGNANCY, CARDIOVASCULAR DISEASE, AND ALL-CAUSE MORTALITY. SOMATIC MUTATIONS IN DNMT3A ARE DRIVERS OF CH, BUT DECADES MAY ELAPSE BETWEEN THE ACQUISITION OF A MUTATION AND CH, SUGGESTING THAT ENVIRONMENTAL FACTORS CONTRIBUTE TO CLONAL EXPANSION. WE TESTED WHETHER INFECTION PROVIDES SELECTIVE PRESSURE FAVORING THE EXPANSION OF DNMT3A MUTANT HEMATOPOIETIC STEM CELLS (HSCS) IN MOUSE CHIMERAS. WE CREATED DNMT3A-MOSAIC MICE BY TRANSPLANTING DNMT3A(-/-) AND WT HSCS INTO WT MICE AND OBSERVED THE SUBSTANTIAL EXPANSION OF DNMT3A(-/-) HSCS DURING CHRONIC MYCOBACTERIAL INFECTION. INJECTION OF RECOMBINANT IFNGAMMA ALONE WAS SUFFICIENT TO PHENOCOPY CH BY DNMT3A(-/-) HSCS UPON INFECTION. TRANSCRIPTIONAL AND EPIGENETIC PROFILING AND FUNCTIONAL STUDIES INDICATE REDUCED DIFFERENTIATION ASSOCIATED WITH WIDESPREAD METHYLATION ALTERATIONS, AND REDUCED SECONDARY STRESS-INDUCED APOPTOSIS ACCOUNTS FOR DNMT3A(-/-) CLONAL EXPANSION DURING INFECTION. DNMT3A MUTANT HUMAN HSCS SIMILARLY EXHIBIT DEFECTIVE IFNGAMMA-INDUCED DIFFERENTIATION. WE THUS DEMONSTRATE THAT IFNGAMMA SIGNALING INDUCED DURING CHRONIC INFECTION CAN DRIVE DNMT3A-LOSS-OF-FUNCTION CH. 2021 20 4593 23 NATURAL GENETIC VARIATION IN A MULTIGENERATIONAL PHENOTYPE IN C. ELEGANS. ALTHOUGH HEREDITY MOSTLY RELIES ON THE TRANSMISSION OF DNA SEQUENCE, ADDITIONAL MOLECULAR AND CELLULAR FEATURES ARE HERITABLE ACROSS SEVERAL GENERATIONS. IN THE NEMATODE CAENORHABDITIS ELEGANS, INSIGHTS INTO SUCH UNCONVENTIONAL INHERITANCE RESULT FROM TWO LINES OF WORK. FIRST, THE MORTAL GERMLINE (MRT) PHENOTYPE WAS DEFINED AS A MULTIGENERATIONAL PHENOTYPE WHEREBY A SELFING LINEAGE BECOMES STERILE AFTER SEVERAL GENERATIONS, IMPLYING MULTIGENERATIONAL MEMORY [1, 2]. SECOND, CERTAIN RNAI EFFECTS ARE HERITABLE OVER SEVERAL GENERATIONS IN THE ABSENCE OF THE INITIAL TRIGGER [3-5]. BOTH LINES OF WORK CONVERGED WHEN THE SUBSET OF MRT MUTANTS THAT ARE HEAT SENSITIVE WERE FOUND TO CLOSELY CORRESPOND TO MUTANTS DEFECTIVE IN THE RNAI-INHERITANCE MACHINERY, INCLUDING HISTONE MODIFIERS [6-9]. HERE, WE REPORT THE SURPRISING FINDING THAT SEVERAL C. ELEGANS WILD ISOLATES DISPLAY A HEAT-SENSITIVE MORTAL GERMLINE PHENOTYPE IN LABORATORY CONDITIONS: UPON CHRONIC EXPOSURE TO HIGHER TEMPERATURES, SUCH AS 25 DEGREES C, LINES REPRODUCIBLY BECOME STERILE AFTER SEVERAL GENERATIONS. THIS PHENOMENON IS REVERSIBLE, AS IT CAN BE SUPPRESSED BY TEMPERATURE ALTERNATIONS AT EACH GENERATION, SUGGESTING A NON-GENETIC BASIS FOR THE STERILITY. WE TESTED WHETHER NATURAL VARIATION IN THE TEMPERATURE-INDUCED MRT PHENOTYPE WAS OF GENETIC NATURE BY BUILDING RECOMBINANT INBRED LINES BETWEEN THE ISOLATES MY10 (MRT) AND JU1395 (NON-MRT). USING BULK SEGREGANT ANALYSIS, WE DETECTED TWO QUANTITATIVE TRAIT LOCI. AFTER FURTHER RECOMBINANT MAPPING AND GENOME EDITING, WE IDENTIFIED THE MAJOR CAUSAL LOCUS AS A POLYMORPHISM IN THE SET-24 GENE, ENCODING A SET- AND SPK-DOMAIN PROTEIN. WE CONCLUDE THAT C. ELEGANS NATURAL POPULATIONS MAY HARBOR NATURAL GENETIC VARIATION IN EPIGENETIC INHERITANCE PHENOMENA. 2018