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Protistology ■ 51
najdrova.vladimira@seznam.cz Giardia intestinalis, an anaerobic protozoan parasite, contains highly compact genome with extremely short untranslated regions (UTRs). The regulation ofgene expression during giardia cell- and life-cycle has been poorly studied and only a handful of RNA binding proteins have been characterized so far. PUF proteins bind 3' UTRs of cognate mRNAs, by which they regulate their stability, translation and localization. These eukaryotic proteins are evolutionarily conserved from protists to metazoans. We have identified five PUF genes in the genome of G. intestinalis and have initiated studies towards the characterization of PUFs in giardia biology.
EXPLORING CELL TYPE DIFFERENTIATION IN THE FILASTEREAN CAPSASPORA OWCZARZAKI BY SINGLE-CELL RNA-SEQ Najle S.R.1, Florenza J.1, Mazutis L.2, Ruiz-Trillo
I 1,3,4
1 - Institut de Biologia Evolutiva (Univesitat Pompeu Fabra — CSIC). Pg. Maritim de la Barceloneta 37-49, 08003, Barcelona, Catalonia, Spain
2 - Institute ofBiotechnology, Vilnius University. V.A. Graiciuno 8, LT-02241, Vilnius, Lithuania
3 - Departament de Genutica, Universitat de Barcelona, Av. Diagonal, 645, Barcelona 08028, Catalonia, Spain
4 - Instituciy Catalana de Recerca i Estudis Avangats (ICREA), Passeig Lluis Companys, 23, Barcelona 08010, Catalonia, Spain. sebastian.najle@upf.edu
The origin of multicellular animals from their unicellular ancestors is one of the most important evolutionary transitions in life's history. However, the specific cellular and genetic changes that led to this transition remain unknown. Phylogenomic analyses have shown that animals are closely related to three unicellular lineages: choanoflagellates, filastereans and ichthyosporeans, altogether forming the Holozoa clade. Recent phylogenomic studies have shown that those premetazoan taxa already had a complex repertoire of genes important for multicellularity, some of them previously thought to be exclusive of animals. Different versions of "simple multicellularity" are found among the unicellular relatives of Metazoa. There is the clonal development of colonial choanoflagellates, the aggregative behavior of Capsaspora owczarzaki, and the coenocytic development of ichthyosporeans. Those colonies and aggregates are assumed to be without cell differentiation. However, there is no molecular data proving that all cells within those colonies or aggregates or coenocytes are identical. Here we show microscopic evidence for the coexis-
tence of different cell types in C. owczarzaki aggregates. We also show our advances in developing single-cell transcriptomics methodology in these organism to molecularly characterize cell types. The possibility of analyzing differential gene expression at the single-cell level between diverse cell types of unicellular holozoans will allow us to better understand the molecular mechanisms underlying programs of cell differentiation in the origin of animals. The aggregates of C. owczarzaki offer us an ideal model in which to test this, and provide a better framework to understand the origin of the different metazoan cell types.
PHYLOGENY AND ECOLOGICAL IMPORTANCE OF PHAEODARIANS (CERCOZOA, RHIZARIA)
Nakamura Y.1, Somiya R.2, Suzuki N.3, Hori S. R.4, Tuji A.1
1 - Department ofBotany, National Museum ofNature and Science
2 - Graduate School of Fisheries Science and Environmental Studies, Nagasaki University
3 - Graduate School ofScience, Tohoku University
4 - Graduate School ofScience and Engineering, Ehime University
y.nakamura@fish.hokudai.ac.jp Phaeodarians are a group of marine protists belonging to the phylum Cercozoa, composing Rhizaria (SAR). These unicellular siliceous zooplankton occasionally become abundant in the ocean, however their ecological importance and phylogeny are still wrapped in mystery. Plankton were sampled from several depths at ca. 40 stations in the Northern hemisphere during 2011—2015. Zooplankton were sorted and identified in order to clarify the species composition of each sample. Some phaeodarians were cultured to observe their behavior. The 18S rDNA sequences of phaeodarians were determined by single-cell PCR method. Two undescribed phaeodarians were found in the deep waters in the Sea of Japan, and one of the species was abundant through the year, occupying ca. 22% of the total zooplankton biomass on average. The abundance of phaeodarians was also seen in the East China Sea, where two species occupied 10.2—13.9% of the zooplankton biomass, suggesting that this group is an important component of the zooplankton community and the material cycle in the ocean. The cell division ofphaeodarians was observed during the culture experiment. The species morphologically identified as phaeodarians formed a single clade together with other cercozoans in the phylogenetic tree, suggesting that almost all phaeodarians belong to Cercozoa and that Phaeodaria is a monophyletic
