Center for Biochemistry, University of Cologne, Cologne, Germany.
Department of Molecular Medicine, Biochemistry Unit, University of Pavia, Pavia, Italy.
Front Endocrinol (Lausanne). 2022 Nov 14;13:1000662. doi: 10.3389/fendo.2022.1000662. eCollection 2022.
COMP (Cartilage Oligomeric Matrix Protein), also named thrombospondin-5, is a member of the thrombospondin family of extracellular matrix proteins. It is of clinical relevance, as in humans mutations in COMP lead to chondrodysplasias. The gene encoding zebrafish Comp is located on chromosome 11 in synteny with its mammalian orthologs. Zebrafish Comp has a domain structure identical to that of tetrapod COMP and shares 74% sequence similarity with murine COMP. Zebrafish is expressed from 5 hours post fertilization (hpf) on, while the protein is first detectable in somites of 11 hpf embryos. During development and in adults is strongly expressed in myosepta, craniofacial tendon and ligaments, around ribs and vertebra, but not in its name-giving tissue cartilage. As in mammals, zebrafish Comp forms pentamers. It is easily extracted from 5 days post fertilization (dpf) whole zebrafish. The lack of Comp expression in zebrafish cartilage implies that its cartilage function evolved recently in tetrapods. The expression in tendon and myosepta may indicate a more fundamental function, as in evolutionary distant Drosophila muscle-specific adhesion to tendon cells requires thrombospondin. A sequence encoding a calcium binding motif within the first TSP type-3 repeat of zebrafish Comp was targeted by CRISPR-Cas. The heterozygous and homozygous mutant Comp zebrafish displayed a patchy irregular Comp staining in 3 dpf myosepta, indicating a dominant phenotype. Electron microscopy revealed that the endoplasmic reticulum of myosepta fibroblasts is not affected in homozygous fish. The disorganized extracellular matrix may indicate that this mutation rather interferes with extracellular matrix assembly, similar to what is seen in a subgroup of chondrodysplasia patients. The early expression and easy detection of mutant Comp in zebrafish points to the potential of using the zebrafish model for large scale screening of small molecules that can improve secretion or function of disease-associated COMP mutants.
COMP（软骨寡聚基质蛋白），也称为血小板反应蛋白 5，是细胞外基质蛋白血小板反应蛋白家族的一员。在人类中，COMP 基因突变导致软骨发育不全，因此具有临床相关性。编码斑马鱼 Comp 的基因位于 11 号染色体上，与哺乳动物同源物具有同线性。斑马鱼 Comp 的结构域结构与四足动物 COMP 相同，与鼠 COMP 具有 74%的序列相似性。斑马鱼从受精后 5 小时（hpf）开始表达，而蛋白质最早可在 11 hpf 胚胎的体节中检测到。在发育过程中和成年期，在肌膜、颅面肌腱和韧带、肋骨和椎骨周围强烈表达，但不在其命名组织软骨中表达。与哺乳动物一样，斑马鱼 Comp 形成五聚体。它可以很容易地从受精后 5 天（dpf）的整条斑马鱼中提取。斑马鱼软骨中缺乏 Comp 表达意味着其软骨功能是在四足动物中最近进化而来的。在肌腱和肌膜中的表达可能表明其具有更基本的功能，因为在进化上遥远的果蝇肌肉特异性粘附到肌腱细胞需要血小板反应蛋白。通过 CRISPR-Cas 靶向斑马鱼 Comp 第一 TSP 型 3 重复内的一个钙结合基序的序列。杂合和纯合突变 Comp 斑马鱼在 3 dpf 肌膜中显示出斑驳不规则的 Comp 染色，表明表现型为显性。电子显微镜显示，纯合鱼的肌膜成纤维细胞的内质网不受影响。细胞外基质的紊乱可能表明这种突变更可能干扰细胞外基质的组装，类似于在软骨发育不全患者的亚组中看到的情况。突变 Comp 在斑马鱼中的早期表达和易于检测表明，使用斑马鱼模型进行大规模筛选可改善与疾病相关的 COMP 突变体分泌或功能的小分子具有潜力。
