Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA.
Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA; Center for Structural Biology, Vanderbilt University, Nashville, TN, USA.
Adv Biol Regul. 2023 Jan;87:100945. doi: 10.1016/j.jbior.2022.100945. Epub 2022 Dec 22.
Mutations in the heterotetrametric adaptor protein 4 (AP-4; ε/β4/μ4/σ4 subunits) membrane trafficking coat complex lead to complex neurological disorders characterized by spastic paraplegia, microcephaly, and intellectual disabilities. Understanding molecular mechanisms underlying these disorders continues to emerge with recent identification of an essential autophagy protein, ATG9A, as an AP-4 cargo. Significant progress has been made uncovering AP-4 function in cell culture and patient-derived cell lines, and ATG9A trafficking by AP-4 is considered a potential target for gene therapy approaches. In contrast, understanding how AP-4 trafficking affects development and function at the organismal level has long been hindered by loss of conserved AP-4 genes in key model systems (S. cerevisiae, C. elegans, D. melanogaster). However, zebrafish (Danio rerio) have retained AP-4 and can serve as an important model system for studying both the nervous system and overall development. We undertook gene editing in zebrafish using a CRISPR-ExoCas9 knockout system to determine how loss of single AP-4, or its accessory protein tepsin, genes affect embryo development 24 h post-fertilization (hpf). Single gene-edited embryos display abnormal head morphology and neural necrosis. We further conducted the first exploration of how AP-4 single gene knockouts in zebrafish embryos affect expression levels and patterns of two autophagy genes, atg9a and map1lc3b. This work suggests zebrafish may be further adapted and developed as a tool to uncover AP-4 function in membrane trafficking and autophagy in the context of a model organism.
异源四聚体衔接蛋白 4(AP-4;ε/β4/μ4/σ4 亚基)膜转运衣被复合物的突变导致以痉挛性截瘫、小头畸形和智力障碍为特征的复杂神经紊乱。随着最近发现必需的自噬蛋白 ATG9A 是 AP-4 货物,这些疾病的分子机制的理解不断涌现。在细胞培养和患者来源的细胞系中,AP-4 功能的显著进展已经被揭示,并且 AP-4 转运 ATG9A 被认为是基因治疗方法的潜在靶点。相比之下,了解 AP-4 转运如何在生物体水平上影响发育和功能,长期以来一直受到关键模型系统(酿酒酵母、秀丽隐杆线虫、黑腹果蝇)中保守的 AP-4 基因缺失的阻碍。然而,斑马鱼(Danio rerio)保留了 AP-4,可以作为研究神经系统和整体发育的重要模型系统。我们使用 CRISPR-ExoCas9 基因编辑系统在斑马鱼中进行基因编辑,以确定单个 AP-4 或其辅助蛋白 tepsin 基因缺失如何影响受精后 24 小时(hpf)胚胎的发育。单个基因编辑胚胎显示出异常的头部形态和神经坏死。我们进一步首次探索了斑马鱼胚胎中 AP-4 单基因敲除如何影响两个自噬基因 atg9a 和 map1lc3b 的表达水平和模式。这项工作表明,斑马鱼可能会进一步被适应和开发,作为揭示模型生物中膜转运和自噬中 AP-4 功能的工具。