Division of Biomedical Sciences, School of Medicine, University of California, Riverside, Riverside, CA, 92521, USA.
Department of Quantitative and Computational Biology, University of Southern California, Los Angeles, CA, 90089, USA.
Nat Commun. 2022 Apr 19;13(1):2081. doi: 10.1038/s41467-022-29786-4.
The gene regulation underlying axon formation and its exclusiveness to neurons remains elusive. TRIM46 is postulated to determine axonal fate. We show Trim46 mRNA is expressed before axonogenesis, but TRIM46 protein level is inhibited by alternative splicing of two cassette exons coupled separately to stability controls of Trim46 mRNA and proteins, effectively inducing functional knockout of TRIM46 proteins. Exon 8 inclusion causes nonsense-mediated mRNA decay of Trim46 transcripts. PTBP2-mediated exon 10 skipping produces transcripts encoding unstable TRIM46 proteins. During axonogenesis, transcriptional activation, decreased exon 8 inclusion, and enhanced exon 10 inclusion converge to increase TRIM46 proteins, leading to its neural-specific expression. Genetic deletion of these exons alters TRIM46 protein levels and shows TRIM46 is instructive though not always required for AnkG localization nor a determinant of AnkG density. Therefore, two concurrently but independently regulated alternative exons orchestrate the temporal induction and tissue-specific expression of TRIM46 proteins to mediate axon formation.
轴突形成及其神经元特异性的基因调控仍然难以捉摸。TRIM46 被假定为决定轴突命运的基因。我们发现 Trim46 mRNA 在轴突发生之前表达，但 TRIM46 蛋白水平受到两个外显子的选择性剪接的抑制，这两个外显子分别与 Trim46 mRNA 和蛋白质的稳定性控制相关联，有效地诱导了 TRIM46 蛋白的功能性缺失。外显子 8 的包含导致 Trim46 转录物的无意义介导的 mRNA 衰变。PTBP2 介导的外显子 10 跳跃产生编码不稳定 TRIM46 蛋白的转录本。在轴突发生过程中，转录激活、外显子 8 的包含减少和外显子 10 的包含增加，共同增加 TRIM46 蛋白，导致其在神经细胞中的特异性表达。这些外显子的遗传缺失改变了 TRIM46 蛋白水平，并表明 TRIM46 是有指导作用的，尽管它并不总是必需的，也不是 AnkG 定位的决定因素，也不是 AnkG 密度的决定因素。因此，两个同时但独立调节的选择性外显子协调 TRIM46 蛋白的时空诱导和组织特异性表达，以介导轴突形成。
