PDF(Pubmed)
Abstract：
Vertebrates have distinct tissues which are not present in invertebrate chordates nor other metazoans. The rise of these tissues also coincided with at least one round of whole-genome duplication as well as a suite of lineage-specific segmental duplications. Understanding whether novel genes lead to the origin and diversification of novel cell types, therefore, is of great importance in vertebrate evolution. Here we were particularly interested in the evolution of the vertebrate musculoskeletal system, the muscles and connective tissues that support a diversity of body plans. A major component of the musculoskeletal extracellular matrix (ECM) is fibrillar collagens, a gene family which has been greatly expanded upon in vertebrates. We thus asked whether the repertoire of fibrillar collagens in vertebrates reflects differences in the musculoskeletal system. To test this, we explored the diversity of fibrillar collagens in lamprey, a jawless vertebrate which diverged from jawed vertebrates (gnathostomes) more than five hundred million years ago and has undergone its own gene duplications. Some of the principal components of vertebrate hyaline cartilage are the fibrillar collagens type II and XI, but their presence in cartilage development across all vertebrate taxa has been disputed. We particularly emphasized the characterization of genes in the lamprey hyaline cartilage, testing if its collagen repertoire was similar to that in gnathostomes. Overall, we discovered thirteen fibrillar collagens from all known gene subfamilies in lamprey and were able to identify several lineage-specific duplications. We found that, while the collagen loci have undergone rearrangement, the Clade A genes have remained linked with the hox clusters, a phenomenon also seen in gnathostomes. While the lamprey muscular tissue was largely similar to that seen in gnathostomes, we saw considerable differences in the larval lamprey skeletal tissue, with distinct collagen combinations pertaining to different cartilage types. Our gene expression analyses were unable to identify type II collagen in the sea lamprey hyaline cartilage nor any other fibrillar collagen during chondrogenesis at the stages observed, meaning that sea lamprey likely no longer require these genes during early cartilage development. Our findings suggest that fibrillar collagens were multifunctional across the musculoskeletal system in the last common ancestor of vertebrates and have been largely conserved, but these genes alone cannot explain the origin of novel cell types.
摘要：
脊椎动物具有不同的组织，在无脊椎动物脊索动物或其他后生动物中都不存在。这些组织的兴起还与至少一轮全基因组复制以及一系列谱系特异性片段复制同时发生。了解新基因是否导致新细胞类型的起源和多样化，因此,在脊椎动物进化中具有重要意义。在这里，我们对脊椎动物肌肉骨骼系统的进化特别感兴趣，支持多种身体计划的肌肉和结缔组织。肌肉骨骼细胞外基质（ECM）的主要成分是纤维状胶原蛋白，在脊椎动物中得到极大扩展的基因家族。因此，我们询问脊椎动物的纤维状胶原蛋白库是否反映了肌肉骨骼系统的差异。为了测试这个，我们探索了七叶鱼中纤维状胶原蛋白的多样性，一种无颚的脊椎动物，在5亿多年前从有颚的脊椎动物（gnathostomes）分化出来，并经历了自己的基因复制。脊椎动物透明软骨的一些主要成分是纤维状胶原II型和XI型，但是它们在所有脊椎动物分类群的软骨发育中的存在一直存在争议。我们特别强调了在七头猎物透明软骨中的基因表征，测试其胶原蛋白库是否与颌骨造口术中的胶原蛋白库相似。总的来说,我们发现了13个纤维状胶原蛋白从所有已知的基因亚家族的七叶鱼，并能够识别几个谱系特异性的重复。我们发现,虽然胶原蛋白位点发生了重排，进化枝A基因与hox簇保持着联系，在颌骨造口术中也看到了一种现象。虽然七叶鱼的肌肉组织与下颌造口术中看到的大部分相似，我们看到幼虫七叶鱼骨骼组织有相当大的差异，具有与不同软骨类型有关的不同胶原蛋白组合。我们的基因表达分析无法在观察到的软骨形成阶段鉴定海七lamp透明软骨中的II型胶原蛋白或任何其他纤维状胶原蛋白。这意味着在软骨的早期发育过程中，海七猎物可能不再需要这些基因。我们的发现表明，在脊椎动物的最后一个共同祖先中，纤维状胶原蛋白在整个肌肉骨骼系统中具有多功能，并且在很大程度上得到了保存，但是这些基因本身并不能解释新细胞类型的起源。
