Cook Geoffrey M, Gruen Anna E, Morris John, Pankey M Sabrina, Senatore Adriano, Katz Paul S, Watson Winsor H, Newcomb James M
Biol Bull. 2018 Jun;234(3):207-218. doi: 10.1086/698467. Epub 2018 Jun 5.
While much is known about the genes and proteins that make up the circadian clocks in vertebrates and several arthropod species, much less is known about the clock genes in many other invertebrates, including nudibranchs. The goal of this project was to identify the RNA and protein products of putative clock genes in the central nervous system of three nudibranchs, Hermissenda crassicornis, Melibe leonina, and Tritonia diomedea. Using previously published transcriptomes (Hermissenda and Tritonia) and a new transcriptome (Melibe), we identified nudibranch orthologs for the products of five canonical clock genes: brain and muscle aryl hydrocarbon receptor nuclear translocator like protein 1, circadian locomotor output cycles kaput, non-photoreceptive cryptochrome, period, and timeless. Additionally, orthologous sequences for the products of five related genes-aryl hydrocarbon receptor nuclear translocator like, photoreceptive cryptochrome, cryptochrome DASH, 6-4 photolyase, and timeout-were determined. Phylogenetic analyses confirmed that the nudibranch proteins were most closely related to known orthologs in related invertebrates, such as oysters and annelids. In general, the nudibranch clock proteins shared greater sequence similarity with Mus musculus orthologs than Drosophila melanogaster orthologs, which is consistent with the closer phylogenetic relationships recovered between lophotrochozoan and vertebrate orthologs. The suite of clock-related genes in nudibranchs includes both photoreceptive and non-photoreceptive cryptochromes, as well as timeout and possibly timeless. Therefore, the nudibranch clock may resemble the one exhibited in mammals, or possibly even in non-drosopholid insects and oysters. The latter would be evidence supporting this as the ancestral clock for bilaterians.
虽然我们对构成脊椎动物和几种节肢动物生物钟的基因和蛋白质了解很多，但对包括裸鳃类动物在内的许多其他无脊椎动物的生物钟基因却知之甚少。本项目的目标是鉴定三种裸鳃类动物——粗壮海兔（Hermissenda crassicornis）、狮鬃海蛞蝓（Melibe leonina）和多氏三歧海牛（Tritonia diomedea）中枢神经系统中假定生物钟基因的RNA和蛋白质产物。利用先前发表的转录组（海兔和三歧海牛）以及一个新的转录组（狮鬃海蛞蝓），我们鉴定出了五个典型生物钟基因产物的裸鳃类直系同源物：脑和肌肉芳烃受体核转运体样蛋白1、昼夜运动输出周期蛋白、非感光隐花色素、周期蛋白和无时间蛋白。此外，还确定了五个相关基因产物的直系同源序列——芳烃受体核转运体样蛋白、感光隐花色素、隐花色素DASH、6 - 4光解酶和超时蛋白。系统发育分析证实，裸鳃类动物的蛋白质与相关无脊椎动物（如牡蛎和环节动物）中已知的直系同源物关系最为密切。总体而言，裸鳃类动物的生物钟蛋白与小家鼠直系同源物的序列相似性高于黑腹果蝇直系同源物，这与在冠轮动物和脊椎动物直系同源物之间发现的更密切的系统发育关系一致。裸鳃类动物中与生物钟相关的基因组合包括感光和非感光隐花色素，以及超时蛋白和可能的无时间蛋白。因此，裸鳃类动物的生物钟可能类似于哺乳动物中表现出的生物钟，甚至可能类似于非果蝇类昆虫和牡蛎中的生物钟。后者将作为支持这是两侧对称动物祖先生物钟的证据。
