In JoVE (1)

Other Publications (8)

Articles by Mariann Micsinai in JoVE

Other articles by Mariann Micsinai on PubMed

The Mammalian Sin3 Proteins Are Required for Muscle Development and Sarcomere Specification

Molecular and Cellular Biology. Dec, 2010  |  Pubmed ID: 20956564

The highly related mammalian Sin3A and Sin3B proteins provide a versatile platform for chromatin-modifying activities. Sin3-containing complexes play a role in gene repression through deacetylation of nucleosomes. Here, we explore a role for Sin3 in myogenesis by examining the phenotypes resulting from acute somatic deletion of both isoforms in vivo and from primary myotubes in vitro. Myotubes ablated for Sin3A alone, but not Sin3B, displayed gross defects in sarcomere structure that were considerably enhanced upon simultaneous ablation of both isoforms. Massively parallel sequencing of Sin3A- and Sin3B-bound genomic loci revealed a subset of target genes directly involved in sarcomere function that are positively regulated by Sin3A and Sin3B proteins. Both proteins were coordinately recruited to a substantial number of genes. Interestingly, depletion of Sin3B led to compensatory increases in Sin3A recruitment at certain target loci, but Sin3B was never found to compensate for Sin3A loss. Thus, our analyses describe a novel transcriptional role for Sin3A and Sin3B proteins associated with maintenance of differentiated muscle cells.

RUNX Transcription Factor-mediated Association of Cd4 and Cd8 Enables Coordinate Gene Regulation

Immunity. Mar, 2011  |  Pubmed ID: 21435585

T cell fate is associated with mutually exclusive expression of CD4 or CD8 in helper and cytotoxic T cells, respectively. How expression of one locus is temporally coordinated with repression of the other has been a long-standing enigma, though we know RUNX transcription factors activate the Cd8 locus, silence the Cd4 locus, and repress the Zbtb7b locus (encoding the transcription factor ThPOK), which is required for CD4 expression. Here we found that nuclear organization was altered by interplay among members of this transcription factor circuitry: RUNX binding mediated association of Cd4 and Cd8 whereas ThPOK binding kept the loci apart. Moreover, targeted deletions within Cd4 modulated CD8 expression and pericentromeric repositioning of Cd8. Communication between Cd4 and Cd8 thus appears to enable long-range epigenetic regulation to ensure that expression of one excludes the other in mature CD4 or CD8 single-positive (SP) cells.

Genome-wide Remodeling of the Epigenetic Landscape During Myogenic Differentiation

Proceedings of the National Academy of Sciences of the United States of America. May, 2011  |  Pubmed ID: 21551099

We have examined changes in the chromatin landscape during muscle differentiation by mapping the genome-wide location of ten key histone marks and transcription factors in mouse myoblasts and terminally differentiated myotubes, providing an exceptionally rich dataset that has enabled discovery of key epigenetic changes underlying myogenesis. Using this compendium, we focused on a well-known repressive mark, histone H3 lysine 27 trimethylation, and identified novel regulatory elements flanking the myogenin gene that function as a key differentiation-dependent switch during myogenesis. Next, we examined the role of Polycomb-mediated H3K27 methylation in gene repression by systematically ablating components of both PRC1 and PRC2 complexes. Surprisingly, we found mechanistic differences between transient and permanent repression of muscle differentiation and lineage commitment genes and observed that the loss of PRC1 and PRC2 components produced opposing differentiation defects. These phenotypes illustrate striking differences as compared to embryonic stem cell differentiation and suggest that PRC1 and PRC2 do not operate sequentially in muscle cells. Our studies of PRC1 occupancy also suggested a "fail-safe" mechanism, whereby PRC1/Bmi1 concentrates at genes specifying nonmuscle lineages, helping to retain H3K27me3 in the face of declining Ezh2-mediated methyltransferase activity in differentiated cells.

Identification of a Claudin-4 and E-cadherin Score to Predict Prognosis in Breast Cancer

Cancer Science. Dec, 2011  |  Pubmed ID: 21883696

The elevated expression of claudins (CLDN) and E-cadherin (CDH-1) was found to correlate with poor prognostic features. Our aim was to perform a comprehensive analysis to assess their potential to predict prognosis in breast cancer. The expression of CLDN-1, -3-5, -7, -8, -10, -15, -18, and E-cadherin at the mRNA level was evaluated in correlation with survival in datasets containing expression measurements of 1809 breast cancer patients. The breast cancer tissues of 197 patients were evaluated with tissue microarray technique and immunohistochemical method for CLDN-1-5, -7, and E-cadherin protein expression. An additional validation set of 387 patients was used to test the accuracy of the resulting prognostic score. Based on the bioinformatic screening of publicly-available datasets, the metagene of CLDN-3, -4, -7, and E-cadherin was shown to have the most powerful predictive power in the survival analyses. An immunohistochemical protein profile consisting of CLDN-2, -4, and E-cadherin was able to predict outcome in the most effective manner in the training set. Combining the overlapping members of the above two methods resulted in the claudin-4 and E-cadherin score (CURIO), which was able to accurately predict relapse-free survival in the validation cohort (P = 0.029). The multivariate analysis, including clinicopathological variables and the CURIO, showed that the latter kept its predictive power (P = 0.040). Furthermore, the CURIO was able to further refine prognosis, separating good versus poor prognosis subgroups in luminal A, luminal B, and triple-negative breast cancer intrinsic subtypes. In breast cancer, the CURIO provides additional prognostic information besides the routinely utilized diagnostic approaches and factors.

Picking ChIP-seq Peak Detectors for Analyzing Chromatin Modification Experiments

Nucleic Acids Research. May, 2012  |  Pubmed ID: 22307239

Numerous algorithms have been developed to analyze ChIP-Seq data. However, the complexity of analyzing diverse patterns of ChIP-Seq signals, especially for epigenetic marks, still calls for the development of new algorithms and objective comparisons of existing methods. We developed Qeseq, an algorithm to detect regions of increased ChIP read density relative to background. Qeseq employs critical novel elements, such as iterative recalibration and neighbor joining of reads to identify enriched regions of any length. To objectively assess its performance relative to other 14 ChIP-Seq peak finders, we designed a novel protocol based on Validation Discriminant Analysis (VDA) to optimally select validation sites and generated two validation datasets, which are the most comprehensive to date for algorithmic benchmarking of key epigenetic marks. In addition, we systematically explored a total of 315 diverse parameter configurations from these algorithms and found that typically optimal parameters in one dataset do not generalize to other datasets. Nevertheless, default parameters show the most stable performance, suggesting that they should be used. This study also provides a reproducible and generalizable methodology for unbiased comparative analysis of high-throughput sequencing tools that can facilitate future algorithmic development.

IL-7 Functionally Segregates the Pro-B Cell Stage by Regulating Transcription of Recombination Mediators Across Cell Cycle

Journal of Immunology (Baltimore, Md. : 1950). Jun, 2012  |  Pubmed ID: 22581861

Ag receptor diversity involves the introduction of DNA double-stranded breaks during lymphocyte development. To ensure fidelity, cleavage is confined to the G(0)-G(1) phase of the cell cycle. One established mechanism of regulation is through periodic degradation of the RAG2 recombinase protein. However, there are additional levels of protection. In this paper, we show that cyclical changes in the IL-7R signaling pathway functionally segregate pro-B cells according to cell cycle status. In consequence, the level of a downstream effector of IL-7 signaling, phospho-STAT5, is inversely correlated with cell cycle expression of Rag, a key gene involved in recombination. Higher levels of phopho-STAT5 in S-G(2) correlate with decreased Rag expression and Rag relocalization to pericentromeric heterochromatin. These cyclical changes in transcription and locus repositioning are ablated upon transformation with v-Abl, which renders STAT5 constitutively active across the cell cycle. We propose that this activity of the IL-7R/STAT5 pathway plays a critical protective role in development, complementing regulation of RAG2 at the protein level, to ensure that recombination does not occur during replication. Our data, suggesting that pro-B cells are not a single homogeneous population, explain inconsistencies in the role of IL-7 signaling in regulating Igh recombination.

Close Proximity to Igh is a Contributing Factor to AID-mediated Translocations

Molecular Cell. Sep, 2012  |  Pubmed ID: 22864115

Class switch recombination (CSR) has the potential to generate genomic instability in B cells as activation-induced cytidine deaminase (AID), which mediates this process, is known to target many sites outside Igh. Nonetheless we do not fully understand what factors influence AID targeting genome-wide. Given that errors in CSR can lead to dangerous, oncogenic chromosomal translocations it is important to identify the elements that determine which genes are at risk of being "hit" and could be involved in aberrant rearrangements. Here we have investigated the influence of nuclear organization in determining "off-target" activity and the choice of fusion partners. Our studies indicate that the vast majority of known AID-mediated Igh translocation partners are found in chromosomal domains that contact this locus during class switching. Further, these interaction domains can be used to identify other genes that are hit by AID.

Integrated Analysis of Tumor Samples Sheds Light on Tumor Heterogeneity

The Yale Journal of Biology and Medicine. Sep, 2012  |  Pubmed ID: 23012583

The heterogeneity of tumor samples is a major challenge in the analysis of high-throughput profiling of tumor biopsies and cell lines. The measured aggregate signals of multigenerational progenies often represent an average of several tumor subclones with varying genomic aberrations and different gene expression levels. The goal of the present study was to integrate copy number analyses from SNP-arrays and karyotyping, gene expression profiling, and pathway analyses to detect heterogeneity, identify driver mutations, and explore possible mechanisms of tumor evolution. We showed the heterogeneity of the studied samples, characterized the global copy number alteration profiles, and identified genes whose copy number status and expression levels were aberrant. In particular, we identified a recurrent association between two BRAF(V600E) and BRAF(V600K) mutations and changes in DKK1 gene expression levels, which might indicate an association between the BRAF and WNT pathways. These findings show that the integrated approaches used in the present study can robustly address the challenging issue of tumor heterogeneity in high-throughput profiling.

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