Supporting data for "The developmental transcriptome atlas of the spoon worm Urechis unicinctus (Echiurida: Annelida)"

Echiurida is one of the most intriguing major subgroups of the phylum Annelida, because unlike most other annelids, echiurids lack metameric body segmentation as adults. For this reason, transcriptome analyses from various developmental stages of Echiurid can be of substantial value for understanding precise expression levels and the complex regulatory networks during early and larval development.
A total of 914 million raw RNA-Seq reads were produced from 14 developmental stages of Urechis unicinctus, and were de novo assembled into contigs spanning 63,928,225 bp with an N50 length of 2,700 bp. The resulting comprehensive transcriptome database of the early developmental stages of U. unicinctus consists of 20,305 representative functional protein-coding transcripts. Approximately 66 % of unigenes were assigned to superphylum-level taxa, including Lophotrochozoa (40%). The completeness of the transcriptome assembly was assessed using BUSCO, and 75.7 % of the metazoan single-copy orthologs were presented in our transcriptome database. We observed three distinct patterns of global transcriptome profiles from 14 developmental stages, and identified a total of 12,705 genes that showed dynamic regulation patterns during the differentiation and maturation of U. unicinctus cells.
We present the first large-scale developmental transcriptome dataset of U. unicinctus and provide a general overview of the dynamics of global gene expression changes during its early developmental stages. The analysis of time-course gene expression data is a first step toward understanding the complex developmental gene regulatory networks in U. unicinctus, and will furnish a valuable resource for analyzing the functions of gene repertoires in various developmental phases.

螠虫目（Echiurida）是环节动物门（Annelida）中颇具研究价值的主要类群之一——与绝大多数其他环节动物不同，成年螠虫不具备分节的身体结构。正因如此，针对螠虫不同发育阶段开展转录组分析，对于解析早期及幼虫发育阶段精准的基因表达水平与复杂调控网络具有重要意义。
研究团队从单环刺螠（Urechis unicinctus）的14个发育阶段中，共获得9.14亿条原始RNA测序（RNA-Seq）读段，经从头组装得到总长63,928,225 bp的重叠群（contig），其N50长度为2700 bp。本研究构建的单环刺螠早期发育阶段综合转录组数据库，共包含20305条具有代表性的功能性蛋白编码转录本。约66%的单基因（unigene）被注释至总界级分类群，其中担轮动物总门（Lophotrochozoa）占比为40%。转录组组装的完整性通过BUSCO工具进行评估，结果显示本数据库覆盖了75.7%的后生动物单拷贝同源基因。
研究团队从14个发育阶段的全局转录组谱中观察到三种显著不同的表达模式，并鉴定出共计12705个在单环刺螠细胞分化与成熟过程中呈现动态调控模式的基因。
本研究首次发布单环刺螠的大规模发育转录组数据集，并全面概述了其早期发育阶段全局基因表达的动态变化。对该时间序列基因表达数据的分析，是解析单环刺螠复杂发育基因调控网络的第一步，也将为解析不同发育阶段的基因功能库提供宝贵的研究资源。