Control of murine brown adipocyte development by GATA6

Brown adipose tissue (BAT) is a thermogenic organ that protects animals against hypothermia and obesity. BAT derives from the multipotent paraxial mesoderm; however, the identity of embryonic brown fat progenitor cells and regulators of adipogenic commitment are unclear. Here, we performed single-cell gene expression analyses of mesenchymal cells during mouse embryogenesis with a focus on BAT development. We identified cell populations associated with the development of BAT, including Dpp4+ cells that emerge at the onset of adipogenic commitment. Immunostaining and lineage-tracing studies show that Dpp4+ cells constitute the BAT fascia and contribute minorly as adipocyte progenitors. Additionally, we identified the transcription factor GATA6 as a marker of brown adipogenic progenitor cells. Deletion of Gata6 in the brown fat lineage resulted in a striking loss of BAT. Together, these results identify progenitor and transitional cells in the brown adipose lineage and define a crucial role for GATA6 in BAT development.

Shared PPARα/γ Target Genes Regulate Brown Adipocyte Thermogenic Function

Brown adipose tissue (BAT) generates heat to maintain body temperature and suppress obesity. Agonists for nuclear receptors PPARα and PPARγ both affect brown adipocyte function, yet the interplay between these factors in BAT is uncertain. Here, we report that PPARα shares most genomic binding sites with PPARγ, and these common binding sites are more related to BAT function than PPARγ-selective sites without PPARα. Integrating PPARα and PPARγ genomic occupancy with cold-responsive BAT transcriptomes identifies a subset of 16 genes with potential relevance to BAT function. Among these, we focused on the lysosomal protease cathepsin Z (CTSZ) and showed it is necessary for mitochondrial respiration in both mouse and human brown adipocytes. Thus, CTSZ is a shared PPARα/γ target gene in BAT and a regulator of brown adipocyte thermogenic function.

Gcn5-Mediated Histone Acetylation Governs Nucleosome Dynamics in Spermiogenesis

During mammalian spermatogenesis, germ cell chromatin undergoes dramatic histone acetylation-mediated reorganization, whereby 90%-99% of histones are evicted. Given the potential role of retained histones in fertility and embryonic development, the genomic location of retained nucleosomes is of great interest. However, the ultimate position and mechanisms underlying nucleosome eviction or retention are poorly understood, including several studies utilizing micrococcal-nuclease sequencing (MNase-seq) methodologies reporting remarkably dissimilar locations. We utilized assay for transposase accessible chromatin sequencing (ATAC-seq) in mouse sperm and found nucleosome enrichment at promoters but also retention at inter- and intragenic regions and repetitive elements. We further generated germ-cell-specific, conditional knockout mice for the key histone acetyltransferase Gcn5, which resulted in abnormal chromatin dynamics leading to increased sperm histone retention and severe reproductive phenotypes. Our findings demonstrate that Gcn5-mediated histone acetylation promotes chromatin accessibility and nucleosome eviction in spermiogenesis and that loss of histone acetylation leads to defects that disrupt male fertility and potentially early embryogenesis.

Natural human genetic variation determines basal and inducible expression of PM20D1, an obesity-associated gene

PM20D1 is a candidate thermogenic enzyme in mouse fat, with its expression cold-induced and enriched in brown versus white adipocytes. Thiazolidinedione (TZD) antidiabetic drugs, which activate the peroxisome proliferator-activated receptor-γ (PPARγ) nuclear receptor, are potent stimuli for adipocyte browning yet fail to induce Pm20d1 expression in mouse adipocytes. In contrast, PM20D1 is one of the most strongly TZD-induced transcripts in human adipocytes, although not in cells from all individuals. Two putative PPARγ binding sites exist near the gene's transcription start site (TSS) in human but not mouse adipocytes. The -4 kb upstream site falls in a segmental duplication of a nearly identical intronic region +2.5 kb downstream of the TSS, and this duplication occurred in the primate lineage and not in other mammals, like mice. PPARγ binding and gene activation occur via this upstream duplicated site, thus explaining the species difference. Furthermore, this functional upstream PPARγ site exhibits genetic variation among people, with 1 SNP allele disrupting a PPAR response element and giving less activation by PPARγ and TZDs. In addition to this upstream variant that determines PPARγ regulation of PM20D1 in adipocytes, distinct variants downstream of the TSS have strong effects on PM20D1 expression in human fat as well as other tissues. A haplotype of 7 tightly linked downstream SNP alleles is associated with very low PMD201 expression and correspondingly high DNA methylation at the TSS. These PM20D1 low-expression variants may account for human genetic associations in this region with obesity as well as neurodegenerative diseases.

Humanized H19/Igf2 locus reveals diverged imprinting mechanism between mouse and human and reflects Silver-Russell syndrome phenotypes

Genomic imprinting affects a subset of genes in mammals, such that they are expressed in a monoallelic, parent-of-origin-specific manner. These genes are regulated by imprinting control regions (ICRs), cis-regulatory elements that exhibit allele-specific differential DNA methylation. Although genomic imprinting is conserved in mammals, ICRs are genetically divergent across species. This raises the fundamental question of whether the ICR plays a species-specific role in regulating imprinting at a given locus. We addressed this question at the H19/insulin-like growth factor 2 (Igf2) imprinted locus, the misregulation of which is associated with the human imprinting disorders Beckwith-Wiedemann syndrome (BWS) and Silver-Russell syndrome (SRS). We generated a knock-in mouse in which the endogenous H19/Igf2 ICR (mIC1) is replaced by the orthologous human ICR (hIC1) sequence, designated H19(hIC1) We show that hIC1 can functionally replace mIC1 on the maternal allele. In contrast, paternally transmitted hIC1 leads to growth restriction, abnormal hIC1 methylation, and loss of H19 and Igf2 imprinted expression. Imprint establishment at hIC1 is impaired in the male germ line, which is associated with an abnormal composition of histone posttranslational modifications compared with mIC1. Overall, this study reveals evolutionarily divergent paternal imprinting at IC1 between mice and humans. The conserved maternal imprinting mechanism and function at IC1 demonstrates the possibility of modeling maternal transmission of hIC1 mutations associated with BWS in mice. In addition, we propose that further analyses in the paternal knock-in H19(+/hIC1) mice will elucidate the molecular mechanisms that may underlie SRS.

Comprehensive analysis of histone post-translational modifications in mouse and human male germ cells

Background

During the process of spermatogenesis, male germ cells undergo dramatic chromatin reorganization, whereby most histones are replaced by protamines, as part of the pathway to compact the genome into the small nuclear volume of the sperm head. Remarkably, approximately 90 % (human) to 95 % (mouse) of histones are evicted during the process. An intriguing hypothesis is that post-translational modifications (PTMs) decorating histones play a critical role in epigenetic regulation of spermatogenesis and embryonic development following fertilization. Although a number of specific histone PTMs have been individually studied during spermatogenesis and in mature mouse and human sperm, to date, there is a paucity of comprehensive identification of histone PTMs and their dynamics during this process.

Results

Here we report systematic investigation of sperm histone PTMs and their dynamics during spermatogenesis. We utilized “bottom-up” nanoliquid chromatography–tandem mass spectrometry (nano-LC–MS/MS) to identify histone PTMs and to determine their relative abundance in distinct stages of mouse spermatogenesis (meiotic, round spermatids, elongating/condensing spermatids, and mature sperm) and in human sperm. We detected peptides and histone PTMs from all four canonical histones (H2A, H2B, H3, and H4), the linker histone H1, and multiple histone isoforms of H1, H2A, H2B, and H3 in cells from all stages of mouse spermatogenesis and in mouse sperm. We found strong conservation of histone PTMs for histone H3 and H4 between mouse and human sperm; however, little conservation was observed between H1, H2A, and H2B. Importantly, across eight individual normozoospermic human semen samples, little variation was observed in the relative abundance of nearly all histone PTMs.

Conclusion

In summary, we report the first comprehensive and unbiased analysis of histone PTMs at multiple time points during mouse spermatogenesis and in mature mouse and human sperm. Furthermore, our results suggest a largely uniform histone PTM signature in sperm from individual humans.

Electronic supplementary material

The online version of this article (doi:10.1186/s13072-016-0072-6) contains supplementary material, which is available to authorized users.

Spontaneous myopathy in the SJL/J mouse: pathology and strength loss

Myopathy has been found to develop spontaneously in 100% of SJL/J mice between 6 and 8 months of age. Extent of muscular involvement and mouse strength were quantified in SJL/J mice and Balb/c control mice 2-16 months old. Muscle from young SJL/J mice exhibited histopathological abnormalities and occasional inflammatory infiltrate. By 6 months, 78% of SJL/J mice had developed active myopathy. By 8 months, all SJL/J mice examined had active disease with a mean of 12.9% of muscle fibers affected. Replacement of muscle fibers by fat and/or collagen began at 10 months and was pronounced by 14 months. Significant decreases in strength scores (total body pulling force) at 6 months and 10 months of age reflected the onset of active myopathy and the onset of muscle degeneration, respectively. The spontaneous onset and 100% incidence of myopathy in the SJL/J mouse line should provide a useful model for idiopathic myopathy.

Nitric oxide production in relation to spontaneous B-cell lymphoma and myositis in SJL mice

SJL mice spontaneously develop B cell lymphomas (historically described as reticulum cell sarcomas) by 12 months of age and inflammatory muscle disease (myositis) by 6 months of age. Tumors originate in mesenteric lymph nodes and in Peyer's patches and resemble human germinal center lymphomas. The growth of reticulum cell sarcomas is completely dependent on cytokine production by normal T cells. The spontaneous myositis, which resembles human idiopathic myositis, is characterized by various abnormalities in skeletal muscle, including infiltration with inflammatory cells consisting primarily of macrophages. The participation of different cytokines in the pathogenesis of the lymphoma and the massive invasion of macrophages into muscle tissues led us to investigate the possible involvement of nitric oxide (NO.), which is known to be synthesized by activated macrophages under inflammatory conditions. Elevated NO. production, measured by urinary nitrate excretion, by SJL mice in comparison with BALB/c control mice was observed as early as 7 weeks of age. Both aging and degree of spontaneous myositis correlated with increased nitric oxide production. Oral administration of N-monomethyl-L-arginine, an inhibitor of nitric oxide synthase (NOS), reduced urinary nitrate excretion and also the severity of myositis. Immunohistochemical analysis revealed the presence of inducible NOS (iNOS) in cells in the spleen, lymph nodes, and skeletal muscle. The iNOS is primarily responsible for the enhanced nitric oxide production. Morphology of cells that stained positive for iNOS was similar to that of macrophages infiltrating into the affected tissues. Chronic production of elevated amounts of nitric oxide by the SJL mice, therefore, provides a useful in vivo model for future studies of cellular damage resulting from endogenously produced NO.in combination with oxygen radicals.

Polyclonal immunoglobulin therapy protects against cardiac damage in experimental coxsackievirus-induced myocarditis

Balb/c male mice infected i.p. with 2 x 10(5) plaque forming units (PFU) of coxsackievirus B3 (CVB3) develop severe myocarditis 7 days later. Studies were performed to determine whether therapy with normal polyclonal immunoglobulin would prevent cardiac inflammation. Partially purified immunoglobulin was derived from pooled mouse serum by ammonium sulphate precipitation. Infected animals given either 100 or 1000 micrograms of this preparation for 2 days prior to infection showed greater than 50% reduction in myocarditis compared to control animals which were infected and given either phosphate buffered saline, human immunoglobulin or monoclonal mouse IgG to an extraneous antigen. Protection did not depend upon inhibition of virus infection since cardiac viral titres were frequently equivalent in control and immunoglobulin-treated groups.

Coxsackievirus-B3-induced myocarditis: virus receptor antibodies modulate myocarditis

Two variants of coxsackievirus group B, type 3 (CVB3) differ in ability to induce myocarditis in Balb/cCUM mice. Infection with the highly pathogenic variant (CVB3M) stimulates autoimmunity to normal cardiocyte antigens, and tissue injury results primarily from an autoreactive cytolytic T lymphocyte (ACTL). Animals infected with the less pathogenic CVB3o variant do not develop ACTL, although CVB3o replicates to high titers in the heart and polyclonal neutralizing antisera fail to distinguish between the two variant virions. The present study uses two IgM mAb derived by fusing spleen cells from CVB3M-infected mice with NS-1 cells. These mAb investigate important differences between the virus variants that may explain why only selected infections trigger autoimmunity. mAb 8A6 is a virus-neutralizing antibody that prevents infection of HeLa cells and cultured cardiocytes by attaching to the virus. mAb 10A1 also interferes with infection but presumably reacts to the virus receptor on the susceptible cells and shows little or no binding to the virions. While 8A6 is equally effective in neutralizing both CVB3o and CVB3M, suggesting that antigenic epitopes on both variants are either identical or highly cross-reactive, 10A1 distinguishes between the variants, suggesting that the pathogenic and less pathogenic viruses use distinct cell surface receptors. Competitive binding studies using radiolabeled CVB3M and either of the unlabeled variants confirm this hypothesis. Both mAb effectively prevent CVB3M-induced cardiac damage in vivo. mAb 10A1 also inhibits autoreactive ACTL lysis of cardiocytes, indicating that the autoimmune effectors may recognize the virus receptor, and that the receptor utilized by a virus may prove important in triggering auto-sensitization.

Coxsackievirus-B3-induced myocarditis: virus receptor antibodies modulate myocarditis

Two variants of coxsackievirus group B, type 3 (CVB3) differ in ability to induce myocarditis in Balb/cCUM mice. Infection with the highly pathogenic variant (CVB3M) stimulates autoimmunity to normal cardiocyte antigens, and tissue injury results primarily from an autoreactive cytolytic T lymphocyte (ACTL). Animals infected with the less pathogenic CVB3o variant do not develop ACTL, although CVB3o replicates to high titers in the heart and polyclonal neutralizing antisera fail to distinguish between the two variant virions. The present study uses two IgM mAb derived by fusing spleen cells from CVB3M-infected mice with NS-1 cells. These mAb investigate important differences between the virus variants that may explain why only selected infections trigger autoimmunity. mAb 8A6 is a virus-neutralizing antibody that prevents infection of HeLa cells and cultured cardiocytes by attaching to the virus. mAb 10A1 also interferes with infection but presumably reacts to the virus receptor on the susceptible cells and shows little or no binding to the virions. While 8A6 is equally effective in neutralizing both CVB3o and CVB3M, suggesting that antigenic epitopes on both variants are either identical or highly cross-reactive, 10A1 distinguishes between the variants, suggesting that the pathogenic and less pathogenic viruses use distinct cell surface receptors. Competitive binding studies using radiolabeled CVB3M and either of the unlabeled variants confirm this hypothesis. Both mAb effectively prevent CVB3M-induced cardiac damage in vivo. mAb 10A1 also inhibits autoreactive ACTL lysis of cardiocytes, indicating that the autoimmune effectors may recognize the virus receptor, and that the receptor utilized by a virus may prove important in triggering auto-sensitization.