脊椎动物具有独特的组织,这些组织不存在于无脊椎动物脊索动物或其他后生动物中。这些组织的兴起也与至少一轮全基因组重复以及一系列谱系特异性节段重复相吻合。因此,了解新基因是否导致新细胞类型的起源和多样化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、支持各种身体计划的肌肉和结缔组织的进化特别感兴趣。肌肉骨骼细胞外基质 (ECM) 的主要成分是纤维状胶原蛋白,这是一个在脊椎动物中得到极大扩展的基因家族。因此,我们询问脊椎动物中纤维状胶原蛋白的组成是否反映了肌肉骨骼系统的差异。为了测试这一点,我们探索了七鳃鳗中纤维状胶原蛋白的多样性,七鳃鳗是一种无颌脊椎动物,它在 5 亿多年前从有颌脊椎动物(有颚动物)中分化出来,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,但它们在所有脊椎动物类群的软骨发育中的存在一直存在争议。我们特别强调了七鳃鳗透明软骨中基因的特征,测试其胶原蛋白库是否与有颚类动物中的相似。全面的,我们从七鳃鳗的所有已知基因亚家族中发现了 13 种纤维状胶原蛋白,并且能够识别出几个谱系特异性重复。我们发现,虽然胶原基因座发生了重排,但 Clade A 基因仍然与霍克斯集群,这种现象也见于有颚类动物。虽然七鳃鳗的肌肉组织与有颚类动物中的肌肉组织非常相似,但我们在幼虫的骨骼组织中发现了相当大的差异,不同的软骨类型具有不同的胶原蛋白组合。我们的基因表达分析无法在观察到的软骨形成过程中鉴定海七鳃鳗透明软骨中的 II 型胶原蛋白或任何其他纤维状胶原蛋白,这意味着海七鳃鳗在早期软骨发育过程中可能不再需要这些基因。我们的研究结果表明,在脊椎动物的最后一个共同祖先的肌肉骨骼系统中,纤维状胶原蛋白具有多功能性,并且在很大程度上是保守的,但这些基因本身并不能解释新细胞类型的起源。
"点击查看英文标题和摘要"
A Comprehensive Analysis of Fibrillar Collagens in Lamprey Suggests a Conserved Role in Vertebrate Musculoskeletal Evolution
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.