Institute of Biology, University of Graz, Universitätsplatz 2, 8010, Graz, Austria.
Department of Biology, University of Antwerp, Groenenborgerlaan 171, 2020, Antwerp, Belgium.
BMC Ecol Evol. 2022 Mar 10;22(1):28. doi: 10.1186/s12862-022-01984-0.
Elasmoid scales are one of the most common dermal appendages and can be found in almost all species of bony fish differing greatly in their shape. Whilst the genetic underpinnings behind elasmoid scale development have been investigated, not much is known about the mechanisms involved in moulding of scales. To investigate the links between gene expression differences and morphological divergence, we inferred shape variation of scales from two different areas of the body (anterior and posterior) stemming from ten haplochromine cichlid species from different origins (Lake Tanganyika, Lake Malawi, Lake Victoria and riverine). Additionally, we investigated transcriptional differences of a set of genes known to be involved in scale development and morphogenesis in fish.
We found that scales from the anterior and posterior part of the body strongly differ in their overall shape, and a separate look on scales from each body part revealed similar trajectories of shape differences considering the lake origin of single investigated species. Above all, nine as well as 11 out of 16 target genes showed expression differences between the lakes for the anterior and posterior dataset, respectively. Whereas in posterior scales four genes (dlx5, eda, rankl and shh) revealed significant correlations between expression and morphological differentiation, in anterior scales only one gene (eda) showed such a correlation. Furthermore, eda displayed the most significant expression difference between species of Lake Tanganyika and species of the other two younger lakes. Finally, we found genetic differences in downstream regions of eda gene (e.g., in the eda-tnfsf13b inter-genic region) that are associated with observed expression differences. This is reminiscent of a genetic difference in the eda-tnfsf13b inter-genic region which leads to gain or loss of armour plates in stickleback.
These findings provide evidence for cross-species transcriptional differences of an important morphogenetic factor, eda, which is involved in formation of ectodermal appendages. These expression differences appeared to be associated with morphological differences observed in the scales of haplochromine cichlids indicating potential role of eda mediated signal in divergent scale morphogenesis in fish.
鲨鱼鳞是最常见的皮肤附属物之一，几乎存在于所有硬骨鱼类中，形状差异很大。虽然已经研究了鲨鱼鳞发育的遗传基础，但对于参与塑造鳞片的机制知之甚少。为了研究基因表达差异与形态分歧之间的联系，我们从来自不同起源的十个口孵非鲫慈鲷物种的身体的两个不同区域（前部和后部）推断出鳞片的形状变化（坦干依喀湖、马拉维湖、维多利亚湖和河流）。此外，我们研究了一组已知参与鱼类鳞片发育和形态发生的基因的转录差异。
我们发现身体前部和后部的鳞片在整体形状上有很大的差异，并且分别观察每个身体部位的鳞片，考虑到单个研究物种的湖泊起源，发现形状差异的轨迹相似。最重要的是，在前后数据集上，有 9 个和 16 个目标基因中的 11 个分别在前湖和后湖中表现出表达差异。虽然在后部鳞片中，有 4 个基因（dlx5、eda、rankl 和 shh）显示出表达与形态分化之间的显著相关性，但在前部鳞片中只有 1 个基因（eda）显示出这种相关性。此外，eda 在坦干依喀湖物种和其他两个年轻湖泊物种之间表现出最显著的表达差异。最后，我们发现 eda 基因下游区域（例如，eda-tnfsf13b 基因间区）的遗传差异与观察到的表达差异相关。这让人想起在棘鱼中，eda-tnfsf13b 基因间区的遗传差异导致了甲胄的获得或丧失。
这些发现为参与外胚层附属物形成的重要形态发生因子 eda 的跨物种转录差异提供了证据。这些表达差异似乎与口孵非鲫慈鲷鳞片中观察到的形态差异有关，表明 eda 介导的信号在鱼类鳞片形态发生中的分化作用。
