Varela Nelson, Aranguiz Alejandra, Lizama Carlos, Sepulveda Hugo, Antonelli Marcelo, Thaler Roman, Moreno Ricardo D, Montecino Martin, Stein Gary S, van Wijnen Andre J, Galindo Mario
Program of Cellular and Molecular Biology, Institute of Biomedical Sciences (ICBM), Faculty of Medicine, University of Chile, Santiago, Chile.
Department of Medical Technology, Faculty of Medicine, University of Chile, Santiago, Chile.
J Cell Physiol. 2016 May;231(5):1001-14. doi: 10.1002/jcp.25188. Epub 2015 Sep 18.
Epigenetic mechanisms mediate the acquisition of specialized cellular phenotypes during tissue development, maintenance and repair. When phenotype-committed cells transit through mitosis, chromosomal condensation counteracts epigenetic activation of gene expression. Subsequent post-mitotic re-activation of transcription depends on epigenetic DNA and histone modifications, as well as other architecturally bound proteins that "bookmark" the genome. Osteogenic lineage commitment, differentiation and progenitor proliferation require the bone-related runt-related transcription factor Runx2. Here, we characterized a non-genomic mRNA mediated mechanism by which osteoblast precursors retain their phenotype during self-renewal. We show that osteoblasts produce maximal levels of Runx2 mRNA, but not protein, prior to mitotic cell division. Runx2 mRNA partitions symmetrically between daughter cells in a non-chromosomal tubulin-containing compartment. Subsequently, transcription-independent de novo synthesis of Runx2 protein in early G1 phase results in increased functional interactions of Runx2 with a representative osteoblast-specific target gene (osteocalcin/BGLAP2) in chromatin. Somatic transmission of Runx2 mRNAs in osteoblasts and osteosarcoma cells represents a versatile mechanism for translational rather than transcriptional induction of this principal gene regulator to maintain osteoblast phenotype identity after mitosis.
表观遗传机制在组织发育、维持和修复过程中介导特定细胞表型的获得。当已确定表型的细胞经历有丝分裂时,染色体凝缩会抵消基因表达的表观遗传激活。随后有丝分裂后的转录重新激活取决于表观遗传的DNA和组蛋白修饰,以及其他“标记”基因组的结构结合蛋白。成骨谱系的定向分化、分化和祖细胞增殖需要与骨相关的 runt 相关转录因子Runx2。在这里,我们描述了一种非基因组mRNA介导的机制,通过该机制成骨细胞前体在自我更新过程中保持其表型。我们发现,成骨细胞在有丝分裂细胞分裂之前产生最大水平的Runx2 mRNA,但不产生蛋白质。Runx2 mRNA在含有微管蛋白的非染色体区室中对称地分配到子细胞中。随后,在G1早期阶段,Runx2蛋白的转录非依赖性从头合成导致Runx2与染色质中代表性的成骨细胞特异性靶基因(骨钙素/BGLAP2)的功能相互作用增加。成骨细胞和骨肉瘤细胞中Runx2 mRNA的体细胞传递代表了一种通用机制,通过这种机制,该主要基因调节因子通过翻译而非转录诱导来维持有丝分裂后成骨细胞表型的同一性。