Rodríguez-Moldes Isabel
Department of Cell Biology and Ecology, University of Santiago de Compostela, Santiago de Compostela, Spain.
Brain Behav Evol. 2009;74(1):20-9. doi: 10.1159/000229010. Epub 2009 Sep 2.
It is essential to consider chondrichthyans (cartilaginous fishes) in analyzing ancestral brain organization because this radiation represents the out-group to all other living gnathostomes (jawed vertebrates). It is particularly crucial to understand the evolution of the telencephalon in chondrichthyans, as this structure develops by evagination (as in most other vertebrates), whereas in most osteichthyans (bony fishes), it develops by eversion, a markedly different process. Among chondrichthyans, the Lesser Spotted Dogfish Scyliorhinus canicula (Elasmobranchii) appears to offer the most potential as a model species for study. Developmental studies of Scyliorhinus have revealed a segmentary pattern in the developing forebrain, similar to that described in other vertebrates, as well as the occurrence of tangential cell migration within the telencephalon, especially in relation to the pallial-subpallial boundary. These observations indicate that major morphogenetic processes thought to be a hallmark of mammalian brains actually existed much earlier in vertebrate phylogeny. In addition, analysis of telencephalic development in Scyliorhinus indicates the existence of telencephalic structures that are probably related to the ganglionic eminences of mammals.
在分析原始脑组织结构时，考虑软骨鱼类是至关重要的，因为这一分类群代表了所有其他现存有颌脊椎动物的外类群。了解软骨鱼类端脑的进化尤为关键，因为该结构通过内陷发育（与大多数其他脊椎动物一样），而在大多数硬骨鱼类中，它通过外翻发育，这是一个明显不同的过程。在软骨鱼类中，小斑点猫鲨（板鳃亚纲）似乎是最具研究潜力的模式物种。对小斑点猫鲨的发育研究揭示了发育中的前脑的节段模式，类似于其他脊椎动物中所描述的模式，以及端脑内切向细胞迁移的发生，特别是与脑皮质-皮质下边界相关的迁移。这些观察结果表明，被认为是哺乳动物脑特征的主要形态发生过程实际上在脊椎动物系统发育中存在得更早。此外，对小斑点猫鲨端脑发育的分析表明存在可能与哺乳动物神经节隆起相关的端脑结构。
