The Molecular and Behavioral Neuroscience Institute and Department of Biological Chemistry, University of Michigan, Ann Arbor Michigan 48109, USA.
J Neurosci. 2012 Jan 18;32(3):1096-109. doi: 10.1523/JNEUROSCI.5603-11.2012.
Unlike mammals, adult zebrafish are able to regenerate multiple tissues including those of the CNS. In the zebrafish retina, injury stimulates Müller glia dedifferentiation into a multipotent retinal progenitor that is capable of regenerating all lost cell types. This dedifferentiation is driven by the reactivation of gene expression programs that share many characteristics with those that operate during early development. Although the mechanisms underlying the reactivation of these programs remain unknown, it is likely that changes in DNA methylation play a significant role. To begin investigating whether DNA demethylation may contribute to retina regeneration, we characterized the expression of genes associated with DNA demethylation in the uninjured and injured retina. We found that two cytidine deaminases (apobec2a and apobec2b) were expressed basally in the uninjured retina and that they were induced in proliferating, dedifferentiated Müller glia. The maximal induction of apobec2b required Ascl1a, but was independent of Lin28, and therefore defines an independent signaling pathway stemming from Ascl1a. Strikingly, when Apobec2a or Apobec2b was knocked down by antisense morpholino oligonucleotides, the proliferative response of Müller glia following injury was significantly reduced and injury-dependent induction of ascl1a and its target genes were inhibited, suggesting the presence of a regulatory feedback loop between Apobec proteins and ascl1a. Finally, Ascl1a, Apobec2a and Apobec2b were found to be essential for optic nerve regeneration. These data identify an essential role for Apobec proteins during retina and optic nerve regeneration and suggest DNA demethylation may underlie the reprogramming of cells to mount a regenerative response.
与哺乳动物不同，成年斑马鱼能够再生多种组织，包括中枢神经系统的组织。在斑马鱼的视网膜中，损伤会刺激 Müller 胶质细胞去分化为多能视网膜祖细胞，该祖细胞能够再生所有丢失的细胞类型。这种去分化是由基因表达程序的重新激活驱动的，这些程序与早期发育过程中运行的程序有许多共同特征。尽管这些程序重新激活的机制尚不清楚，但 DNA 甲基化的变化很可能起着重要作用。为了开始研究 DNA 去甲基化是否可能有助于视网膜再生，我们研究了未受伤和受伤的视网膜中与 DNA 去甲基化相关的基因的表达情况。我们发现，两种胞嘧啶脱氨酶（apobec2a 和 apobec2b）在未受伤的视网膜中基础表达，并在增殖、去分化的 Müller 胶质细胞中诱导表达。apobec2b 的最大诱导需要 Ascl1a，但不依赖于 Lin28，因此定义了一个独立的信号通路，源自 Ascl1a。引人注目的是，当 Apobec2a 或 Apobec2b 被反义 morpholino 寡核苷酸敲低时，损伤后 Müller 胶质细胞的增殖反应显著降低，并且损伤依赖性诱导的 ascl1a 及其靶基因被抑制，这表明 Apobec 蛋白和 ascl1a 之间存在调节反馈回路。最后，发现 Ascl1a、Apobec2a 和 Apobec2b 对视神经再生是必需的。这些数据表明 Apobec 蛋白在视网膜和视神经再生过程中起着重要作用，并表明 DNA 去甲基化可能是细胞重新编程以产生再生反应的基础。
