DataSheet10_Diversification of habenular organization and asymmetries in teleosts: Insights from the Atlantic salmon and European eel.pdf

Habenulae asymmetries are widespread across vertebrates and analyses in zebrafish, the reference model organism for this process, have provided insight into their molecular nature, their mechanisms of formation and their important roles in the integration of environmental and internal cues with a variety of organismal adaptive responses. However, the generality of the characteristics identified in this species remains an open question, even on a relatively short evolutionary scale, in teleosts. To address this question, we have characterized the broad organization of habenulae in the Atlantic salmon and quantified the asymmetries in each of the identified subdomains. Our results show that a highly conserved partitioning into a dorsal and a ventral component is retained in the Atlantic salmon and that asymmetries are mainly observed in the former as in zebrafish. A remarkable difference is that a prominent left-restricted pax6 positive nucleus is observed in the Atlantic salmon, but undetectable in zebrafish. This nucleus is not observed outside teleosts, and harbors a complex presence/absence pattern in this group, retaining its location and cytoarchitectonic organization in an elopomorph, the European eel. These findings suggest an ancient origin and high evolvability of this trait in the taxon. Taken together, our data raise novel questions about the variability of asymmetries across teleosts and their biological significance depending on ecological contexts.

缰核不对称性（habenulae asymmetries）广泛存在于脊椎动物中，以斑马鱼（zebrafish）作为该研究方向的参考模式生物的相关分析，已为其分子本质、形成机制，以及其在整合环境与内部信号以调控多种机体适应性反应中发挥的重要作用提供了深入见解。然而，即便在硬骨鱼纲（teleosts）这一相对较短的进化尺度内，该物种中发现的特征是否具有普遍性仍是一个悬而未决的问题。为解答这一问题，本研究对大西洋鲑（Atlantic salmon）的缰核整体结构进行了表征，并对已识别的各亚结构域的不对称性进行了定量分析。研究结果显示，大西洋鲑保留了高度保守的背腹分区结构，且与斑马鱼一致，不对称性主要出现在背侧亚区。一个显著差异在于，大西洋鲑中存在一个突出的左侧特异性pax6阳性核团（pax6 positive nucleus），而斑马鱼中无法检测到该结构。该核团仅存在于硬骨鱼纲中，且在该类群中呈现出复杂的存在/缺失模式；在鳗鲡总目（elopomorph）的欧洲鳗鲡（European eel）中，该核团保留了其原有位置与细胞构筑结构。这些发现表明，该特征在该类群中具有古老的起源与高度的演化可塑性。综上，本研究数据提出了全新的科学问题：硬骨鱼纲内缰核不对称性的变异模式，以及其随生态环境变化的生物学意义。