Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.
Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, 119071, Russia.
Sci Rep. 2016 Dec 23;6:39849. doi: 10.1038/srep39849.
Accumulated evidence indicates that the core genetic mechanisms regulating early patterning of the brain rudiment in vertebrates are very similar to those operating during development of the anterior region of invertebrate embryos. However, the mechanisms underlying the morphological differences between the elaborate vertebrate brain and its simpler invertebrate counterpart remain poorly understood. Recently, we hypothesized that the emergence of the most anterior unit of the vertebrate brain, the telencephalon, could be related to the appearance in vertebrates' ancestors of a unique homeobox gene, Anf/Hesx1(further Anf), which is absent from all invertebrates and regulates the earliest steps of telencephalon development in vertebrates. However, the failure of Anf to be detected in one of the most basal extant vertebrate species, the lamprey, seriously compromises this hypothesis. Here, we report the cloning of Anf in three lamprey species and demonstrate that this gene is indeed expressed in embryos in the same pattern as in other vertebrates and executes the same functions by inhibiting the expression of the anterior general regulator Otx2 in favour of the telencephalic regulator FoxG1. These results are consistent with the hypothesis that the Anf homeobox gene may have been important in the evolution of the telencephalon.
积累的证据表明，调节脊椎动物脑原基早期模式形成的核心遗传机制与在无脊椎动物胚胎前区发育过程中起作用的机制非常相似。然而，脊椎动物复杂的大脑与其简单的无脊椎动物对应物之间形态差异的机制仍知之甚少。最近，我们假设脊椎动物大脑最前端单元——端脑的出现可能与脊椎动物祖先中出现的一种独特的同源盒基因 Anf/Hesx1（进一步称为 Anf）有关，该基因在所有无脊椎动物中均不存在，并且调节脊椎动物端脑发育的最早步骤。然而， Anf 在现存最基础的脊椎动物物种之一——七鳃鳗中未被检测到，这严重影响了这一假设。在这里，我们在三种七鳃鳗物种中克隆了 Anf，并证明该基因确实以与其他脊椎动物相同的模式在胚胎中表达，并通过抑制前一般调节剂 Otx2 的表达来促进端脑调节剂 FoxG1 的表达，从而执行相同的功能。这些结果与 Anf 同源盒基因可能在端脑进化中很重要的假设是一致的。
