Graduate School of Medicine, University of the Ryukyus, Nishihara-cho, Okinawa 903-0215, Japan,
Misaki Marine Biological Station, University of Tokyo, Miura, Kanagawa 238-0225, Japan.
Zoolog Sci. 2020 Dec;37(6):563-574. doi: 10.2108/zs190140.
Amphibians exhibit phenotypic plasticity, which allows flexible adaptation to fluctuating environments. Although genes involved in expression of plastic phenotypes have been identified, the endocrine bases of plastic responses are largely unknown. Larvae of the Hokkaido salamander () plastically display distinct phenotypes, an "offensive phenotype" characterized as larger body with broadened gape and a "defensive phenotype" characterized as enlarged gills and tail and less active behavior, in the presence of prey larval amphibians and predatory larval dragonfly, respectively. In the presence of both prey and predators, the degree of induction of both phenotypes is reduced, suggesting cross-talk between the molecular signaling pathways of these phenotypes. We conducted a transcriptomic analysis to examine how endocrine regulation affects the phenotypic expression by focusing on the pituitary gland. We found that five endocrine genes, i.e., calcitonin related polypeptide alpha (), growth hormone (), neuropeptide B (), parathyroid hormone 2 (), and prolactin 1 (), were involved in the expression of both phenotypes. However, we conducted only RNA-seq analysis, and no confirmation of significant up-regulation or down-regulation has been conducted. These results suggest that these genes were up-regulated for induction of the offensive phenotype and down-regulated for induction of the defensive phenotype. Phylogenetic analysis indicated that possible gene duplications of and have occurred during amphibian evolution. Based on these findings, it is suggested that a trade-off of molecular signaling pathways exists between the two distinct phenotypic expressions. The results also suggest that hormonal-gene duplications might have contributed to the acquisition of phenotypic plasticity in amphibians.
两栖动物表现出表型可塑性，这使其能够灵活适应不断变化的环境。尽管已经鉴定出参与表型表达的基因，但对可塑性反应的内分泌基础知之甚少。北海道蝾螈幼虫在存在猎物幼体两栖动物和捕食性幼体蜻蜓时，分别表现出明显的表型，一种是“进攻型表型”，特征为体型较大，口裂较宽；另一种是“防御型表型”，特征为鳃和尾巴增大，行为不活跃。在同时存在猎物和捕食者的情况下，两种表型的诱导程度降低，表明这些表型的分子信号通路之间存在串扰。我们进行了转录组分析，通过专注于脑垂体，研究内分泌调节如何影响表型表达。我们发现五个内分泌基因，即降钙素相关多肽α ()、生长激素 ()、神经肽 B ()、甲状旁腺激素 2 () 和催乳素 1 ()，参与了两种表型的表达。然而，我们仅进行了 RNA-seq 分析，尚未对显著上调或下调进行确认。这些结果表明，这些基因上调是为了诱导进攻型表型，下调是为了诱导防御型表型。系统发育分析表明，在两栖动物进化过程中可能发生了 和 的基因复制。基于这些发现，表明两种不同表型表达之间存在分子信号通路的权衡。结果还表明，激素基因的复制可能有助于两栖动物获得表型可塑性。
