Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Department of Neuroscience, University of Texas Southwestern Medical School, Dallas, TX 75390, USA.
Cell Rep. 2020 Mar 31;30(13):4459-4472.e6. doi: 10.1016/j.celrep.2020.02.076.
Silencing of FMR1 and loss of its gene product, FMRP, results in fragile X syndrome (FXS). FMRP binds brain mRNAs and inhibits polypeptide elongation. Using ribosome profiling of the hippocampus, we find that ribosome footprint levels in Fmr1-deficient tissue mostly reflect changes in RNA abundance. Profiling over a time course of ribosome runoff in wild-type tissue reveals a wide range of ribosome translocation rates; on many mRNAs, the ribosomes are stalled. Sucrose gradient ultracentrifugation of hippocampal slices after ribosome runoff reveals that FMRP co-sediments with stalled ribosomes, and its loss results in decline of ribosome stalling on specific mRNAs. One such mRNA encodes SETD2, a lysine methyltransferase that catalyzes H3K36me3. Chromatin immunoprecipitation sequencing (ChIP-seq) demonstrates that loss of FMRP alters the deployment of this histone mark. H3K36me3 is associated with alternative pre-RNA processing, which we find occurs in an FMRP-dependent manner on transcripts linked to neural function and autism spectrum disorders.
FMR1 的沉默和其基因产物 FMRP 的缺失导致脆性 X 综合征（FXS）。FMRP 结合脑 mRNA 并抑制多肽延伸。通过对海马体的核糖体进行分析，我们发现 Fmr1 缺陷组织中的核糖体足迹水平主要反映了 RNA 丰度的变化。在野生型组织中进行核糖体流出的时间过程分析揭示了广泛的核糖体迁移率；在许多 mRNA 上，核糖体被停滞。核糖体流出后对海马切片进行蔗糖梯度超速离心，显示 FMRP 与停滞的核糖体共沉降，其缺失导致特定 mRNA 上核糖体停滞的减少。其中一种 mRNA 编码 SETD2，一种赖氨酸甲基转移酶，催化 H3K36me3。染色质免疫沉淀测序（ChIP-seq）表明 FMRP 的缺失改变了这种组蛋白标记的分布。H3K36me3 与选择性前 RNA 加工有关，我们发现，在与神经功能和自闭症谱系障碍相关的转录物上，这种前 RNA 加工以依赖于 FMRP 的方式发生。
