Forebrain Architecture and Development in Cyclostomes, with Reference to the Early Morphology and Evolution of the Vertebrate Head
Forebrain Architecture and Development in Cyclostomes, with Reference to the Early Morphology and Evolution of the Vertebrate Head
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DOI：
10.1159/000519026
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发表时间：
2021-09
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通讯作者：
F. Sugahara;Y. Murakami;Juan Pascual-Anaya;S. Kuratani
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作者：
F. Sugahara;Y. Murakami;Juan Pascual-Anaya;S. Kuratani
脊椎动物的头部和大脑具有高度复杂的形态特征。前脑是大脑的最前部，从神经节细分为前脑，再分为间脑、下丘脑和端脑。重要的是，端脑包含大脑皮层，大脑皮层在人类高级认知功能中起着关键作用。为了阐明前脑区域化的演化，对现存的有颌脊椎动物和无颌脊椎动物的脑发育进行比较分析是至关重要的。环口类是现存的唯一的无颌脊椎动物，5亿多年前从有颌类脊椎动物分化而来。以前对环口鱼脑的发育研究主要是在七鳃鳗身上进行的，因为七鳃鳗胚胎很少。虽然仍然很少，但最近可获得的八目鳗胚胎已经推动了对大脑发育和基因表达的比较研究。通过与环口动物和无颌脊椎动物化石的发现相结合，我们可以描绘脊椎动物最后的共同祖先大脑的形态、发育机制甚至进化路径。在这篇综述中，我们总结了环口动物前脑的发育，并提出了在脑进化过程中每个环口世系所经历的进化变化。此外，结合CT扫描技术揭示的脊椎动物化石头部形态的最新进展，讨论了颅面形态的演变与前脑向冠口发育机制的变化是如何因果联系的。
The vertebrate head and brain are characterized by highly complex morphological patterns. The forebrain, the most anterior division of the brain, is subdivided into the diencephalon, hypothalamus, and telencephalon from the neuromeric subdivision into prosomeres. Importantly, the telencephalon contains the cerebral cortex, which plays a key role in higher order cognitive functions in humans. To elucidate the evolution of the forebrain regionalization, comparative analyses of the brain development between extant jawed and jawless vertebrates are crucial. Cyclostomes – lampreys and hagfishes – are the only extant jawless vertebrates, and diverged from jawed vertebrates (gnathostomes) over 500 million years ago. Previous developmental studies on the cyclostome brain were conducted mainly in lampreys because hagfish embryos were rarely available. Although still scarce, the recent availability of hagfish embryos has propelled comparative studies of brain development and gene expression. By integrating findings with those of cyclostomes and fossil jawless vertebrates, we can depict the morphology, developmental mechanism, and even the evolutionary path of the brain of the last common ancestor of vertebrates. In this review, we summarize the development of the forebrain in cyclostomes and suggest what evolutionary changes each cyclostome lineage underwent during brain evolution. In addition, together with recent advances in the head morphology in fossil vertebrates revealed by CT scanning technology, we discuss how the evolution of craniofacial morphology and the changes of the developmental mechanism of the forebrain towards crown gnathostomes are causally related.