Project description:RNA microarray analyses revealed that nuclear actin activated many human transcription factor genes including OCT4, which is required for gene reprogramming. OCT4 is known to be activated by nuclear actin in Xenopus oocytes. Our findings imply that this process of OCT4 activation is conserved in vertebrates and among cell types, and could be used for gene reprogramming of human cells.
Project description:Chavez2009 - a core regulatory network of OCT4 in human embryonic stem cells
A core OCT4-regulated network has been identified as a test case, to analyase stem cell characteristics and cellular differentiation.
This model is described in the article:
In silico identification of a core regulatory network of OCT4 in human embryonic stem cells using an integrated approach.
Chavez L, Bais AS, Vingron M, Lehrach H, Adjaye J, Herwig R
BMC Genomics, 2009, 10:314
Abstract:
BACKGROUND: The transcription factor OCT4 is highly expressed in pluripotent embryonic stem cells which are derived from the inner cell mass of mammalian blastocysts. Pluripotency and self renewal are controlled by a transcription regulatory network governed by the transcription factors OCT4, SOX2 and NANOG. Recent studies on reprogramming somatic cells to induced pluripotent stem cells highlight OCT4 as a key regulator of pluripotency.
RESULTS: We have carried out an integrated analysis of high-throughput data (ChIP-on-chip and RNAi experiments along with promoter sequence analysis of putative target genes) and identified a core OCT4 regulatory network in human embryonic stem cells consisting of 33 target genes. Enrichment analysis with these target genes revealed that this integrative analysis increases the functional information content by factors of 1.3 - 4.7 compared to the individual studies. In order to identify potential regulatory co-factors of OCT4, we performed a de novo motif analysis. In addition to known validated OCT4 motifs we obtained binding sites similar to motifs recognized by further regulators of pluripotency and development; e.g. the heterodimer of the transcription factors C-MYC and MAX, a prerequisite for C-MYC transcriptional activity that leads to cell growth and proliferation.
CONCLUSION: Our analysis shows how heterogeneous functional information can be integrated in order to reconstruct gene regulatory networks. As a test case we identified a core OCT4-regulated network that is important for the analysis of stem cell characteristics and cellular differentiation. Functional information is largely enriched using different experimental results. The de novo motif discovery identified well-known regulators closely connected to the OCT4 network as well as potential new regulators of pluripotency and differentiation. These results provide the basis for further targeted functional studies.
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Project description:Pluripotency and lineage commitment in embryonic stem cells depend on coordinated regulation of chromatin architecture and extracellular matrix (ECM) signaling. Here, we identify nuclear β-actin as a key regulator linking these processes in mouse embryonic stem cells. Loss of β-actin disrupts core pluripotency factors, including Oct4 and Sox2, and causes broad transcriptional changes, while nuclear re-expression rescues these defects. Chromatin accessibility analysis revealed reduced accessibility at regulatory regions of pluripotency genes, consistent with impaired chromatin remodeling. β-actin depletion also altered ECM-related gene expression, matrix properties, and cellular biomechanics, leading to impaired self-renewal, skewed lineage specification, and defective differentiation, particularly reduced neuronal potential and increased mesodermal-like fate bias. In vivo, β-actin loss restricted teratoma growth and compromised tri-lineage differentiation. Together, these results define nuclear β-actin as an important regulator of chromatin accessibility, ECM-dependent signaling, and stem cell fate.
Project description:Pluripotency and lineage commitment in embryonic stem cells depend on coordinated regulation of chromatin architecture and extracellular matrix (ECM) signaling. Here, we identify nuclear β-actin as a key regulator linking these processes in mouse embryonic stem cells. Loss of β-actin disrupts core pluripotency factors, including Oct4 and Sox2, and causes broad transcriptional changes, while nuclear re-expression rescues these defects. Chromatin accessibility analysis revealed reduced accessibility at regulatory regions of pluripotency genes, consistent with impaired chromatin remodeling. β-actin depletion also altered ECM-related gene expression, matrix properties, and cellular biomechanics, leading to impaired self-renewal, skewed lineage specification, and defective differentiation, particularly reduced neuronal potential and increased mesodermal-like fate bias. In vivo, β-actin loss restricted teratoma growth and compromised tri-lineage differentiation. Together, these results define nuclear β-actin as an important regulator of chromatin accessibility, ECM-dependent signaling, and stem cell fate.
Project description:Pluripotency and lineage commitment in embryonic stem cells depend on coordinated regulation of chromatin architecture and extracellular matrix (ECM) signaling. Here, we identify nuclear β-actin as a key regulator linking these processes in mouse embryonic stem cells. Loss of β-actin disrupts core pluripotency factors, including Oct4 and Sox2, and causes broad transcriptional changes, while nuclear re-expression rescues these defects. Chromatin accessibility analysis revealed reduced accessibility at regulatory regions of pluripotency genes, consistent with impaired chromatin remodeling. β-actin depletion also altered ECM-related gene expression, matrix properties, and cellular biomechanics, leading to impaired self-renewal, skewed lineage specification, and defective differentiation, particularly reduced neuronal potential and increased mesodermal-like fate bias. In vivo, β-actin loss restricted teratoma growth and compromised tri-lineage differentiation. Together, these results define nuclear β-actin as an important regulator of chromatin accessibility, ECM-dependent signaling, and stem cell fate.
Project description:Nuclear actin participates in many essential cellular processes including gene transcription, chromatic remodelling and mRNA processing. Actin shuttles into and out the nucleus through the action of dedicated transport receptors importin-9 and exportin-6, but how this transport is regulated remains unclear. Here we show that RASSF1A is a novel regulator of actin nucleocytoplasmic trafficking and is required for the active maintenance of nuclear actin levels through supporting binding of exportin-6 (XPO6) to RAN GTPase. RASSF1A (Ras association domain family 1 isoform A) is a tumor suppressor gene frequently silenced by promoter hypermethylation in all major solid cancers. Specifically, we demonstrate that endogenous RASSF1A localizes to the nuclear envelope (NE) and is required for nucleo-cytoplasmic actin transport and the concomitant regulation of Myocardin-related transcription factor A (MRTF-A), a coactivator of the transcription factor serum response factor (SRF). The RASSF1A/RAN/XPO6/nuclear actin pathway is aberrant in cancer cells where RASSF1A expression is lost and correlates with reduced MTRF/SRF activity leading to cell adhesion defects. Taken together, we have identified a previously unknown mechanism by which the nuclear actin pool is regulated and uncovered a previously unknown link of RASSF1A and MTRF/SRF in tumor suppression.
Project description:The nucleosome is a fundamental unit of chromatin in eukaryotes, and generally prevents the binding of transcription factors to genomic DNA. Pioneer transcription factors overcome the nucleosome barrier, and bind their target DNA sequences in chromatin. OCT4 is a representative pioneer transcription factor that plays a role in stem cell pluripotency. In the present study, we biochemically analyzed the nucleosome binding by OCT4. Crosslinking mass spectrometry showed that OCT4 binds the nucleosome.