Department of Biological Sciences, University of Massachusetts Lowell, Lowell, MA, United States of America.
Section of Genetics and Metabolism, University of Arkansas for Medical Sciences, Little Rock, AR, United States of America.
Bone. 2019 Oct;127:488-498. doi: 10.1016/j.bone.2019.07.017. Epub 2019 Jul 17.
Special AT-rich sequence binding protein 2 (Satb2) is a matrix attachment region (MAR) binding protein. Satb2 impacts skeletal development by regulating gene transcription required for osteogenic differentiation. Although its role as a high-order transcription factor is well supported, other roles for Satb2 in skeletal development remain unclear. In particular, the impact of dosage sensitivity (heterozygous mutations) and variance on phenotypic severity is still not well understood. To further investigate molecular and cellular mechanisms of Satb2-mediated skeletal defects, we used the CRISPR/Cas9 system to generate Satb2 mutations in MC3T3-E1 cells. Our data suggest that, in addition to its role in differentiation, Satb2 regulates progenitor proliferation. We also find that mutations in Satb2 cause chromatin defects including nuclear blebbing and donut-shaped nuclei. These defects may contribute to a slight increase in apoptosis in mutant cells, but apoptosis is insufficient to explain the proliferation defects. Satb2 expression exhibits population-level variation and is most highly expressed from late G1 to late G2. Based on these data, we hypothesize that Satb2 may regulate proliferation through two separate mechanisms. First, Satb2 may regulate the expression of genes necessary for cell cycle progression in pre-osteoblasts. Second, similar to other MAR-binding proteins, Satb2 may participate in DNA replication. We also hypothesize that variation in the severity or penetrance of Satb2-mediated proliferation defects is due to stochastic variation in Satb2 binding to DNA, which may be buffered in some genetic backgrounds. Further elucidation of the role of Satb2 in proliferation has potential impacts on our understanding of both skeletal defects and cancer.
富含特殊 AT 的序列结合蛋白 2（Satb2）是一种基质附着区（MAR）结合蛋白。Satb2 通过调节成骨分化所需的基因转录来影响骨骼发育。尽管其作为高级转录因子的作用得到了很好的支持，但 Satb2 在骨骼发育中的其他作用仍不清楚。特别是，剂量敏感性（杂合突变）和变异性对表型严重程度的影响仍不清楚。为了进一步研究 Satb2 介导的骨骼缺陷的分子和细胞机制，我们使用 CRISPR/Cas9 系统在 MC3T3-E1 细胞中生成 Satb2 突变。我们的数据表明，Satb2 除了在分化中起作用外，还调节祖细胞增殖。我们还发现 Satb2 突变会导致染色质缺陷，包括核泡和甜甜圈形核。这些缺陷可能导致突变细胞中凋亡略有增加，但凋亡不足以解释增殖缺陷。Satb2 表达表现出群体水平的变异，在 G1 晚期到 G2 晚期表达最高。基于这些数据，我们假设 Satb2 可能通过两种独立的机制来调节增殖。首先，Satb2 可能调节成骨前体细胞中细胞周期进程所需基因的表达。其次，类似于其他 MAR 结合蛋白，Satb2 可能参与 DNA 复制。我们还假设 Satb2 介导的增殖缺陷的严重程度或外显率的差异是由于 Satb2 与 DNA 的结合存在随机变异，而这种变异在某些遗传背景中可能被缓冲。进一步阐明 Satb2 在增殖中的作用可能会对我们理解骨骼缺陷和癌症产生影响。
