Kozmik Zbynek
Institute of Molecular Genetics of the Czech Academy of Sciences, Prague, Czech Republic.
Int J Dev Biol. 2017;61(10-11-12):571-574. doi: 10.1387/ijdb.170332zk.
The amphioxus (lancelet) was first described by Pallas in 1774 and incorrectly assigned to mollusks. Since then, amphioxus attracted generations of zoologists. It took however almost one hundred years until Alexander Kowalevsky recognized that the larval stages of amphioxus had much in common with vertebrate embryos. Widely studied around 1900 as the 'elementary vertebrate', amphioxus as a model went out of fashion with the decline of comparative anatomy. Due to the scarcity of taxa at the invertebrate-to-vertebrate transition, amphioxus nevertheless remained the species with a privileged position in animal phylogeny. Its resurrection as the popular model of evolutionary developmental biology came with the advent of modern molecular biology and genomics. In the 1990s amphioxus developmental control genes were identified and characterized at a fast pace with the hope that such studies could provide novel insight into an important evolutionary transition: the origin of vertebrates. Indeed, amphioxus was found to be vertebrate-like but much simpler. Its body resembles that of the vertebrate, but it lacks most of the complexities associated with typical vertebrate organs. Its genome is only 1/6 of the human genome and it has not undergone the whole genome duplications that occurred in the vertebrate lineage. For all of these reasons, amphioxus became widely regarded as a useful proxy for the primitive ancestor of all vertebrates. A persistent problem interpreting amphioxus in the phylogenetic context is the difficulty to distinguish ancestral features, and those that are secondarily derived. There is no doubt that an integrative approach combining information from various disciplines is needed in order to help resolve such issues. Anatomy and comparative morphology has always been strong since the dawn of amphioxus research. Recent developments such as the availability of genomic sequences for three Branchiostoma species, established laboratory cultures of amphioxus that can be spawned at the investigator's will, or techniques allowing transgenesis and gene knockouts represent a major leap for studies on how the genotype generates a phenotype. These advances also enable the smooth transition of amphioxus from the model system of a distinguished past into the one with a very bright future.
文昌鱼于1774年首次由帕拉斯描述，并被错误地归类为软体动物。从那时起，文昌鱼吸引了一代又一代的动物学家。然而，直到亚历山大·科瓦列夫斯基认识到文昌鱼的幼虫阶段与脊椎动物胚胎有许多共同之处，差不多花了一百年的时间。1900年左右，文昌鱼作为“原始脊椎动物”被广泛研究，随着比较解剖学的衰落，它作为一种模型不再流行。由于在无脊椎动物向脊椎动物过渡阶段的分类单元稀缺，文昌鱼在动物系统发育中仍然处于特权地位。随着现代分子生物学和基因组学的出现，它作为进化发育生物学的流行模型得以复兴。在20世纪90年代，文昌鱼发育控制基因被迅速鉴定和表征，人们希望这些研究能够为一个重要的进化转变——脊椎动物的起源提供新的见解。事实上，文昌鱼被发现与脊椎动物相似但要简单得多。它的身体与脊椎动物相似，但缺乏与典型脊椎动物器官相关的大多数复杂性。它的基因组只有人类基因组的1/6，并且没有经历脊椎动物谱系中发生的全基因组复制。由于所有这些原因，文昌鱼被广泛认为是所有脊椎动物原始祖先的有用代表。在系统发育背景下解释文昌鱼时，一个持续存在的问题是难以区分祖先特征和次生衍生特征。毫无疑问，需要一种综合各学科信息的方法来帮助解决这些问题。自从文昌鱼研究开始以来，解剖学和比较形态学一直很强。最近的进展，如三种文昌鱼物种基因组序列的可得性、建立了可根据研究者意愿产卵的文昌鱼实验室培养物，或允许转基因和基因敲除的技术，代表了在研究基因型如何产生表型方面的重大飞跃。这些进展也使文昌鱼能够顺利地从过去著名的模型系统转变为具有非常光明未来的模型系统。
