TY - JOUR

T1 - Deletion of HP1γ in cardiac myocytes affects H4K20me3 levels but does not impact cardiac growth

AU - Oyama, Kyohei

AU - El-Nachef, Danny

AU - Fang, Chen

AU - Kajimoto, Hidemi

AU - Brown, Jeremy P.

AU - Singh, Prim B.

AU - MacLellan, W. Robb

PY - 2018/4/17

Y1 - 2018/4/17

N2 - Background: Heterochromatin, which is formed when tri-methyl lysine 9 of histone H3 (H3K9me3) is bound by heterochromatin 1 proteins (HP1s), plays an important role in differentiation and senescence by silencing cell cycle genes. Cardiac myocytes (CMs) accumulate heterochromatin during differentiation and demethylation of H3K9me3 inhibits cell cycle gene silencing and cell cycle exit in CMs; however, it is unclear if this process is mediated by HP1s. In this study, we created a conditional CM-specific HP1 gamma (HP1γ) knockout (KO) mouse model and tested whether HP1γ is required for cell cycle gene silencing and cardiac growth. Results: HP1γ KO mice were generated by crossing HP1γ floxed mice (fl) with mice expressing Cre recombinase driven by the Nkx2.5 (cardiac progenitor gene) promoter (Cre). We confirmed that deletion of critical exons of HP1γ led to undetectable levels of HP1γ protein in HP1γ KO (Cre;fl/fl) CMs. Analysis of cardiac size and function by echo revealed no significant differences between HP1γ KO and control (WT, Cre, fl/fl) mice. No significant difference in expression of cell cycle genes or cardiac-specific genes was observed. Global transcriptome analysis demonstrated a very moderate effect of HP1γ deletion on global gene expression, with only 51 genes differentially expressed in HP1γ KO CMs. We found that HP1β protein, but not HP1α, was significantly upregulated and that subnuclear localization of HP1β to perinuclear heterochromatin was increased in HP1γ KO CMs. Although HP1γ KO had no effect on H3K9me3 levels, we found a significant reduction in another major heterochromatin mark, tri-methylated lysine 20 of histone H4 (H4K20me3). Conclusions: These data indicate that HP1γ is dispensable for cell cycle exit and normal cardiac growth but has a significant role in maintaining H4K20me3 and regulating a limited number of genes in CMs.

AB - Background: Heterochromatin, which is formed when tri-methyl lysine 9 of histone H3 (H3K9me3) is bound by heterochromatin 1 proteins (HP1s), plays an important role in differentiation and senescence by silencing cell cycle genes. Cardiac myocytes (CMs) accumulate heterochromatin during differentiation and demethylation of H3K9me3 inhibits cell cycle gene silencing and cell cycle exit in CMs; however, it is unclear if this process is mediated by HP1s. In this study, we created a conditional CM-specific HP1 gamma (HP1γ) knockout (KO) mouse model and tested whether HP1γ is required for cell cycle gene silencing and cardiac growth. Results: HP1γ KO mice were generated by crossing HP1γ floxed mice (fl) with mice expressing Cre recombinase driven by the Nkx2.5 (cardiac progenitor gene) promoter (Cre). We confirmed that deletion of critical exons of HP1γ led to undetectable levels of HP1γ protein in HP1γ KO (Cre;fl/fl) CMs. Analysis of cardiac size and function by echo revealed no significant differences between HP1γ KO and control (WT, Cre, fl/fl) mice. No significant difference in expression of cell cycle genes or cardiac-specific genes was observed. Global transcriptome analysis demonstrated a very moderate effect of HP1γ deletion on global gene expression, with only 51 genes differentially expressed in HP1γ KO CMs. We found that HP1β protein, but not HP1α, was significantly upregulated and that subnuclear localization of HP1β to perinuclear heterochromatin was increased in HP1γ KO CMs. Although HP1γ KO had no effect on H3K9me3 levels, we found a significant reduction in another major heterochromatin mark, tri-methylated lysine 20 of histone H4 (H4K20me3). Conclusions: These data indicate that HP1γ is dispensable for cell cycle exit and normal cardiac growth but has a significant role in maintaining H4K20me3 and regulating a limited number of genes in CMs.

KW - Cardiac myocytes

KW - Cell cycle

KW - Conditional knockout

KW - Gene expression

KW - H3K9me3

KW - H4K20me3

KW - HP1γ

KW - Gene Expression Profiling/methods

KW - Gene Expression Regulation

KW - Chromosomal Proteins, Non-Histone/genetics

KW - Gene Knockout Techniques

KW - Histones/metabolism

KW - Animals

KW - Cell Cycle Proteins/genetics

KW - Cell Differentiation

KW - Mice

KW - Methylation

KW - Myocytes, Cardiac/cytology

KW - DROSOPHILA-MELANOGASTER

KW - CHROMOSOMAL-PROTEIN

KW - MAMMALIAN CHROMATIN

KW - HP1 gamma

KW - HISTONE H3

KW - HP1

KW - CONSTITUTIVE HETEROCHROMATIN

KW - SHADOW DOMAIN

KW - RETINOBLASTOMA PROTEIN

KW - LYSINE-9 METHYLATION

KW - DIFFERENTIAL EXPRESSION ANALYSIS

UR - http://www.scopus.com/inward/record.url?scp=85045582009&partnerID=8YFLogxK

U2 - 10.1186/s13072-018-0187-z

DO - 10.1186/s13072-018-0187-z

M3 - Article

C2 - 29665845

AN - SCOPUS:85045582009

VL - 11

SP - 18

JO - Epigenetics and Chromatin

JF - Epigenetics and Chromatin

SN - 1756-8935

IS - 1

M1 - 18

ER -