MiR-92 Family Members Form a Cluster Required for Notochord Tubulogenesis in Urochordate Ciona savignyi

MicroRNAs are frequently clustered in the genome and polycistronically transcribed, regulating targeted genes in diverse signaling pathways. The miR-17-92 cluster is a typical miRNA cluster, playing crucial roles in the organogenesis and homeostasis of physiological processes in vertebrates. Here, we identified three miRNAs (csa-miR-92a, csa-miR-92b, and csa-miR-92c) that belonged to the miR-92 family and formed a miRNA cluster in the genome of a urochordate marine ascidian Ciona savignyi. Except for miR-92a and miR-92b, other homologs of the vertebrate miR-17-92 cluster members could not be identified in the Ciona genome. We further found that the mature sequences of urochordate miR-92 family members were highly conserved compared with the vertebrate species. The expression pattern revealed that three miR-92 family members had consistent expression levels in adult tissues and were predominantly expressed in heart and muscle tissue. We further showed that, at the embryonic and larval stages, csa-miR-92c was expressed in the notochord of embryos during 18–31 h post fertilization (hpf) by in situ hybridization. Knockout of csa-miR-92c resulted in the disorganization of notochord cells and the block of lumen coalescence in the notochord. Fibroblast growth factor (FGF), mitogen-activated protein kinase (MAPK), and wingless/integrated (Wnt)/planar cell polarity (PCP) signaling pathways might be involved in the regulatory processes, since a large number of core genes of these pathways were the predicted target genes of the miR-92 family. Taken together, we identified a miR-92 cluster in urochordate Ciona and revealed the expression patterns and the regulatory roles of its members in organogenesis. Our results provide expression and phylogenetic data on the understanding of the miR-92 miRNA cluster’s function during evolution.

The Ascidiacea collected during the 2017 British Columbia Hakai MarineGEO BioBlitz

A three-week intensive marine biodiversity survey was carried out at a small remote region of the central British Columbia coast at and near the Calvert Island Marine Station (Hakai Institute) July 21–August 11, 2017. The survey included daily sampling by the staff and a number of visiting taxonomists with specialties covering all the major groups of invertebrates. Many marine habitats were sampled: rocky and sand/gravel intertidal and tidepools, eelgrass meadows, shallow and deeper subtidal by snorkel and Scuba, plus artificial surfaces including the sides and bottom of the large floating dock at the Institute and settlement plates set out up to a year previously at various subtidal sites. Many new species were recorded by all the taxonomists. In this very biodiverse remote area 36 ascidian species were identified: 18 Aplousobranchia, 7 Phlebobranchia, and 11 Stolidobranchia, comprising a total of 15 solitary and 21 colonial species including two undescribed colonial species. This represents almost one third of all the known North American species from Alaska to southern California in this limited very remote area. Remarkably, only two are possible non-natives. Diplosoma listerianum (Milne-Edwards, 1841), was collected mostly on natural substrates including deeper areas sampled by Scuba, and one colony occurred on a settlement plate. A few Ciona savignyi Herdman, 1882 were collected, two from natural substrates and four from artificial surfaces. There were no botryllids, Styela clava Herdman, 1881, Didemnum vexillum Kott, 2002, or Molgula manhattensis (De Kay, 1843), though these are all common and sometimes very abundant non-natives in other parts of BC and along much of the U.S. west coast. Most of the species encountered are known in northern California, Washington, and southern BC, but only a small number are represented among the few known Alaska species.