ABSTRACT
The larvacean Oikopleura dioica is a fast-developing chordate because of its small number of cells (∼4500 in juveniles) and rapid development to complete morphogenesis by 10 h after fertilization. Strikingly, most of its blastomeres are restricted to give rise to a single cell-type by the 32-cell stage of embryogenesis, unlike cell fate determination at the 110-cell stage in ascidians. In this study, RNA-sequencing (RNA-seq) revealed non-canonical properties of O. dioica: (1) an initial zygotic gene expression of 950 genes at the 16- to 32-cell stage; (2) 25 transcription factors (TFs) are expressed in the 32-cell stage (fewer than half of the TFs underlying gene regulatory networks in ascidian embryogenesis were lost or not expressed); (3) five maternal mRNAs localized in the vegetal-posterior blastomeres in animal and vegetal hemispheres; and (4) three maternal mRNAs localized in the small vegetal pole region of unfertilized eggs. These observations indicate that this fast-developing chordate lacks the first phase of development in ascidians: fertilization-driven ooplasmic movements that drive postplasmic RNAs toward the vegetal pole. These data have been deposited in ANISEED (https://www.aniseed.fr/) as transcriptome resources.
Footnotes
Author contributions
Conceptualization: H.N., T.A.O.; Methodology: R.S., N.M., M.M., Y.P., M.S., Y.S., N.M.L., P.L., T.A.O.; Software: K.W., Y.S., N.M.L., C.D., P.L., A.T.; Validation: K.W., H.N., T.A.O.; Formal analysis: K.W., R.S., M.M., H.N.; Investigation: K.W., R.S., N.M., M.M., Y.P., H.N., T.A.O.; Resources: K.W., C.D., P.L., A.T., H.N., T.A.O.; Data curation: K.W., M.S., Y.S., N.M.L., C.D., P.L., T.A.O.; Writing - original draft: H.N., T.A.O.; Writing - review & editing: K.W., R.S., N.M.L., C.D., T.A.O.; Visualization: T.A.O.; Supervision: T.A.O.; Project administration: T.A.O.; Funding acquisition: H.N., T.A.O.
Funding
This work was supported by the Japan Society for the Promotion of Science (KAKENHI grant 16H06279), by the Ministry of Education, Culture, Sports, Science and Technology KAKENHI (221S0002), by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (26840079, 18K06256, 18H04763 and 20H05946 to T.A.O.; 26650079, 15H04377, 16K14735, 17KT0023 and 19H03234 to H.N.), by the Inamori Foundation (2015) (to T.A.O.), by the Kato Memorial Research Foundation (2015-2016) (to T.A.O.), by the Sumitomo Foundation (2016-2017) (to T.A.O.) and by the Japan Foundation for Applied Enzymology (2017, 2019) (to T.A.O.).
Data availability
The raw RNA-seq data have been deposited in the National Center for Biotechnology Information (accession numbers DRA005714 and DRA005711) and the Gene Expression Omnibus (GEO) repository (GSE139330 and GSE195613). Transcript sequences and proteins sequences can be retrieved from the ANISEED (https://www.aniseed.fr/).
