bCorrect reprogramming of epigenetic marks in the donor nuclei is crucial for successful cloning by nuclear transfer. Specific epigenetic modifications, such as repressive histone lysine methylation marks, are known to be very stable and difficult to reprogram. The discovery of histone lysine demethylases has opened up opportunities to study the effects of removing repressive histone lysine methylation marks in donor cells prior to nuclear transfer. In this study, we generated mouse embryonic stem (ES) cells for the inducible expression of JMJD2B (also known as KDM4B), a demethylase that primarily removes the histone-3 lysine-9 trimethylation (H3K9me3) mark. Induction of jmjd2b in the ES cells decreased total levels of H3K9me3 by 63%. When these cells were used for nuclear transfer, H3K9me3 levels were normalized within minutes following fusion with an enucleated oocyte. This transient reduction of H3K9me3 levels improved in vitro development into cloned embryos by 30%. Despite sharing the same genetic information, cell types within an individual are morphologically and functionally diverse. Diversity arises from a complex set of epigenetic modifications, such as DNA methylation and histone modifications, that control cell-specific gene expression profiles and determine the cellular phenotype. Correct setting of these modifications is critical during embryonic development (1-6). Reprogramming of epigenetic marks occurs first during gametogenesis and later during fertilization and subsequent embryonic differentiation (3, 5). Reprogramming during gametogenesis involves extensive demethylation and sex-specific remethylation at imprinted loci of primordial germ cells and gametes (3). Following fertilization, reprogramming of epigenetic marks is essential for resolving the early parental asymmetry in histone modifications, DNA methylation, and chromatin proteins to allow correct embryonic gene activation (7-9). Nuclear transfer (NT) cloning is almost a reversal of this process. It requires that the genome of a single differentiated cell with all its epigenetic modifications, which, unlike the gametes, are not formatted to initiate development, be reprogrammed from a restricted cell lineage-appropriate gene expression profile to a totipotent state (2, 4). Live cloned offspring have been produced from a range of mammalian species, demonstrating that somatic donor nuclei can be reprogrammed back to the embryonic state (10, 11). However, the efficiency of this process remains low, and various molecular, cellular, and developmental abnormalities have been detected in clones. Incorrect reprogramming of the epigenetic donor cell marks has been proposed to be the main cause of this low efficiency (1, 2, 4, 6).To facilitate nuclear reprogramming, epigenetic modifications in donor cells have been modified by treating them with pharmacological histone deacetylase and DNA methyltransferase inhibitors (12-15). These agents increase global histone acetylation and reduce DNA methylation, respectively, resulting in a more open, tran...

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Correct reprogramming of epigenetic marks is essential for somatic cells to regain pluripotency. Repressive histone (H) lysine (K) methylation marks are known to be stable and difficult to reprogram. In this study, we generated transgenic mice and mouse embryonic fibroblasts (MEFs) for the inducible expression of KDM4B, a demethylase that removes H3 K9 and H3K36 trimethylation (me3) marks (H3K9/36me3). Upon inducing Kdm4b, H3K9/36me3 levels significantly decreased compared to non-induced controls. Concurrently, H3K9me1 levels significantly increased, while H3K9me2 and H3K27me3 remained unchanged. The global transcriptional impact of Kdm4b-mediated reduction in H3K9/36me3 levels was examined by comparative microarray analysis and mRNA-sequencing of three independent transgenic MEF lines. We identified several commonly up-regulated targets, including the heterochromatin-associated zinc finger protein 37 and full-length endogenous retrovirus repeat elements. Following optimized zona-free somatic nuclear transfer, reduced H3K9/36me3 levels were restored within hours. Nevertheless, hypo-methylated Kdm4b MEF donors reprogrammed six-fold better into cloned blastocysts than non-induced donors. They also reprogrammed nine-fold better into induced pluripotent stem cells that gave rise to teratomas and chimeras. In summary, we firmly established H3K9/36me3 as a major roadblock to somatic cell reprogramming and identified transcriptional targets of derestricted chromatin that could contribute towards improving this process in mouse.

Cohesin, a multi-subunit protein complex involved in chromosome organization, is frequently mutated or aberrantly expressed in cancer. Multiple functions of cohesin, including cell division and gene expression, highlight its potential as a novel therapeutic target. The SMC3 subunit of cohesin is acetylated (ac) during S phase to establish cohesion between replicated chromosomes. Following anaphase, ac-SMC3 is deacetylated by HDAC8. Reversal of SMC3 acetylation is imperative for recycling cohesin so that it can be reloaded in interphase for both non-mitotic and mitotic functions. We blocked deacetylation of ac-SMC3 using an HDAC8-specific inhibitor PCI-34051 in MCF7 breast cancer cells, and examined the effects on transcription of cohesin-dependent genes that respond to estrogen. HDAC8 inhibition led to accumulation of ac-SMC3 as expected, but surprisingly, had no influence on the transcription of estrogen-responsive genes that are altered by siRNA targeting of RAD21 or SMC3. Knockdown of RAD21 altered estrogen receptor ␣ (ER) recruitment at SOX4 and IL20, and affected transcription of these genes, while HDAC8 inhibition did not. Rather, inhibition of HDAC8 delayed cell cycle progression, suppressed proliferation and induced apoptosis in a concentration-dependent manner. We conclude that HDAC8 inhibition does not change the estrogen-specific transcriptional role of cohesin in MCF7 cells, but instead, compromises cell cycle progression and cell survival. Our results argue that candidate inhibitors of cohesin function may differ in their effects depending on the cellular genotype and should be thoroughly tested for predicted effects on cohesin's mechanistic roles.The cohesin complex is a chromatin-associated multi-subunit protein comprised of two SMC (structural maintenance of chromosomes, SMC1A and SMC3) 2 and two non-SMC subunits (RAD21, STAG1/2). Cohesin's canonical function establishes cohesion between replicated sister chromatids, thus ensuring their precise segregation at anaphase (1, 2). Research over the last one and a half decades has revealed that cohesin has additional cohesion-independent functions in interphase nuclei, such as chromatin organization and transcription regulation (3, 4).Recently, cancer genome sequencing projects have revealed that genes encoding cohesin subunits are frequently mutated in several different types of cancer, with particularly high frequency in acute myeloid leukemia (AML) (5-9). Recent mouse models indicate that cohesin contributes to leukemia progression likely through controlling transcription and genome organization, rather than through chromosome separation (10 -12). In breast cancer, the cohesin subunit RAD21 is overexpressed and confers poor prognosis (13,14). We previously showed that cohesin mediates transcription of the MYC gene (15-17) and modulates the transcription of estrogen-dependent genes in MCF7 breast cancer cells (18). The emergence of cohesin as an important contributor to cancer has generated interest in the development of therapeutics that compromise ...