Transcriptomic analysis of zebrafish prion protein mutants supports conserved cross-species function of the cellular prion protein

Cellular Prion Protein (PrPC) is a well-studied protein as the substrate for various progressive untreatable neurodegenerative diseases. Normal functions of PrPC are poorly understood, though recent proteomic and transcriptomic approaches have begun to reveal common themes. We use our compound prp1 and prp2 knockout mutant zebrafish at three days post fertilization to take a transcriptomic approach to investigating potentially conserved PrPC functions during development. Gene ontology analysis shows the biological processes with the largest changes in gene expression include redox processing, transport and cell adhesion. Within these categories several different gene families were prevalent including the solute carrier proteins, cytochrome p450 enzymes and protocadherins. Continuing from previous studies identifying cell adhesion as an important function of PrPC we found that in addition to the protocadherins there was a significant reduction in transcript abundance of both ncam1a and st8sia2. These two genes are involved in the early development of vertebrates. The alterations in cell adhesion transcripts were consistent with past findings in zebrafish and mouse prion protein mutants; however E-cadherin processing after prion protein knockdown failed to reveal any differences compared with wild type in either our double prp1/prp2 mutant fish or after prp1 morpholino knockdown. Our data supports a cross species conserved role for PrPC in the development and maintenance of the central nervous system, particularly by regulating various and important cell adhesion processes.细胞型朊蛋白（Cellular Prion Protein, PrPC）是一类被广泛研究的蛋白，作为多种进行性、无法治愈的神经退行性疾病的作用底物。尽管近期蛋白质组学和转录组学研究已开始揭示部分共性规律，但PrPC的正常生理功能仍尚未完全阐明。本研究选取受精后3天的prp1与prp2双基因敲除复合突变斑马鱼，采用转录组学方法探究发育过程中PrPC可能存在的保守性功能。基因本体（Gene Ontology, GO）分析显示，基因表达变化最显著的生物学过程包括氧化还原调控、物质转运与细胞黏附。在这些类别中，多个基因家族的表达变化尤为显著，包括溶质载体蛋白家族、细胞色素P450酶家族以及原钙粘蛋白家族。延续此前将细胞黏附认定为PrPC重要功能的研究，我们发现除原钙粘蛋白外，ncam1a与st8sia2的转录本丰度均出现显著下调。这两个基因均参与脊椎动物的早期发育过程。细胞黏附相关转录本的表达变化与此前在斑马鱼和朊蛋白敲除小鼠中的研究结果一致；不过，无论是在本研究的prp1/prp2双突变斑马鱼中，还是在prp1吗啉代寡核苷酸敲低的样本中，朊蛋白敲低后的E-钙粘蛋白加工过程均未显示出与野生型样本存在显著差异。本研究数据证实，PrPC在中枢神经系统的发育与维持中存在跨物种保守的功能，尤其是通过调控多种关键的细胞黏附过程实现这一作用。