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• Dudin, Omaya; Ondracka, Andrej; Grau-Bové, Xavier; Haraldsen, Arthur Alexander Blørstad; Toyoda, Atsushi & Suga, Hiroshi [Show all 8 contributors for this article] (2019). A unicellular relative of animals generates an epithelium-like cell layer by actomyosin-dependent cellularization. BioRxiv. ISSN 0362-4331. doi: 10.1101/563726. Full text in Research Archive
• Dudin, Omaya; Ondracka, Andrej; Grau-Bové, Xavier; Haraldsen, Arthur Alexander Blørstad; Toyoda, Atsushi & Suga, Hiroshi [Show all 8 contributors for this article] (2019). A unicellular relative of animals generates a layer of polarized cells by actomyosin-dependent cellularization. eLIFE. 8, p. 1–27. doi: 10.7554/eLife.49801. Full text in Research Archive Show summary

  In animals, cellularization of a coenocyte is a specialized form of cytokinesis that results in the formation of a polarized epithelium during early embryonic development. It is characterized by coordinated assembly of an actomyosin network, which drives inward membrane invaginations. However, whether coordinated cellularization driven by membrane invagination exists outside animals is not known. To that end, we investigate cellularization in the ichthyosporean Sphaeroforma arctica, a close unicellular relative of animals. We show that the process of cellularization involves coordinated inward plasma membrane invaginations dependent on an actomyosin network and reveal the temporal order of its assembly. This leads to the formation of a polarized layer of cells resembling an epithelium. We show that this stage is associated with tightly regulated transcriptional activation of genes involved in cell adhesion. Hereby we demonstrate the presence of a self-organized, clonally-generated, polarized layer of cells in a unicellular relative of animals.

• Bråte, Jon; Neumann, Ralf Stefan; Fromm, Bastian; Haraldsen, Arthur Alexander Blørstad; Tarver, James E. & Suga, Hiroshi [Show all 11 contributors for this article] (2018). Unicellular origin of the animal microRNA machinery. Current Biology. ISSN 0960-9822. 28(20), p. 3288–3295.e5. doi: 10.1016/j.cub.2018.08.018. Full text in Research Archive Show summary

  The emergence of multicellular animals was associated with an increase in phenotypic complexity and with the acquisition of spatial cell differentiation and embryonic development. Paradoxically, this phenotypic transition was not paralleled by major changes in the underlying developmental toolkit and regulatory networks. In fact, most of these systems are ancient, established already in the unicellular ancestors of animals [1, 2, 3, 4, 5]. In contrast, the Microprocessor protein machinery, which is essential for microRNA (miRNA) biogenesis in animals, as well as the miRNA genes themselves produced by this Microprocessor, have not been identified outside of the animal kingdom [6]. Hence, the Microprocessor, with the key proteins Pasha and Drosha, is regarded as an animal innovation [7, 8, 9]. Here, we challenge this evolutionary scenario by investigating unicellular sister lineages of animals through genomic and transcriptomic analyses. We identify in Ichthyosporea both Drosha and Pasha (DGCR8 in vertebrates), indicating that the Microprocessor complex evolved long before the last common ancestor of animals, consistent with a pre-metazoan origin of most of the animal developmental gene elements. Through small RNA sequencing, we also discovered expressed bona fide miRNA genes in several species of the ichthyosporeans harboring the Microprocessor. A deep, pre-metazoan origin of the Microprocessor and miRNAs comply with a view that the origin of multicellular animals was not directly linked to the innovation of these key regulatory components.

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• Haraldsen, Arthur Alexander Blørstad (2017). Unicellular origin of the Microprocessor and microRNAs. Full text in Research Archive
• Haraldsen, Arthur Alexander Blørstad; Bråte, Jon; Neumann, Ralf Stefan; Fromm, Bastian; Grini, Paul Eivind & Shalchian-Tabrizi, Kamran (2016). Pre-metazoan origin of animal microRNAs. Full text in Research Archive
• Haraldsen, Arthur Alexander Blørstad; Bjorbækmo, Marit Markussen; Mangot, Jean-Francois; Fuss, Janina; Shalchian-Tabrizi, Kamran & Hansen, Haakon [Show all 7 contributors for this article] (2015). Protist diversity in a marine and lacustrine system: Patterns across a salinity gradient. Full text in Research Archive Show summary

  During the last decade, the improvement of high-throughput sequencing (HTS) techniques has substantially increased our insight into microbial ecology, by capturing a much more detailed picture of their diversity. Due to the increasing amount of data obtained by HTS methods, specific questions on the biogeography and factors explaining the distribution of these microorganisms can now be fully examined. Here, the composition and structure of a metabolically active benthic protistan community was investigated along a salinity gradient of closely associated marine and freshwater systems. Amplicons of rDNA and rRNA, were sequenced using the Illumina MiSeq technology. This approach seemed to successfully capture the majority of the protist community in these habitats. The marine environments displayed a higher species richness compared to the lacustrine systems investigated, and a considerable difference in protist composition was observed between marine and freshwater systems. Nevertheless, some protists were found in both saline and freshwater environments, indicating the ability to survive rather diverse environmental conditions. It is noteworthy that some of the OTUs from both habitats form putative new clades in the enigmatic X-cell group.

• Bjorbækmo, Marit Markussen; Neumann, Ralf Stefan; Haraldsen, Arthur Alexander Blørstad & Shalchian-Tabrizi, Kamran (2015). HIDDEN PROTIST PARASITES: HOW CAN THEY BE DETECTED? Full text in Research Archive
• Bjorbækmo, Marit Markussen; Neumann, Ralf Stefan; Haraldsen, Arthur Alexander Blørstad & Shalchian-Tabrizi, Kamran (2015). Expanding our knowledge about parasites using PATHOS-DB (The PArasiTe–HOSt-DataBase). Full text in Research Archive
• Haraldsen, Arthur Alexander Blørstad (2014). Protist diversity across a marine - freshwater gradient with a special focus on the X-cell parasite. Universitetet i Oslo. Full text in Research Archive Show summary

  Protists are a highly abundant and diverse group of microorganisms that hold important ecological roles in all aquatic ecosystems. Phototrophic protists are responsible for a large portion of the global primary production, and constitute an important food source for many organisms an every trophic level. Heterotrophic protists have key roles in numerous food chains, e.g. as predators regulating prokaryotic densities, and as parasites imposing a strong influence on host populations. Protistan diversity has increasingly been studied in both marine and freshwater systems, but still the majority of protist taxa remain unknown. In recent years, the improvement of high-throughput sequencing techniques has allowed for a higher sequencing depth than before. This influx of sequence data has provided the opportunity to capture a much more detailed picture of microbial diversity, making it possible to further study their distribution and biogeography. In the present study, the composition and structure of the benthic protist community along a natural salinity gradient (from a marine and a lacustrine system) has been investigated using the Illumina MiSeq sequencing approach. Both rDNA and rRNA were sequenced from sediment samples, in order to obtain an assessment of the metabolically active community, and to relate this to biophysicochemical factors measured in the respective environments. In addition, special emphasize was given to a specific protist parasite group, the X-cell, with intention of detecting its diversity and distribution in these marine and freshwater environments. Generally, a huge diversity of protists was uncovered, displaying several patterns in community composition and structure related to environmental factors. A considerable difference in protist composition was observed between marine and freshwater systems. This was demonstrated to be affected by variation in the salinity concentration. Nevertheless, some protists were found in both saline and freshwater environments, indicating the ability to survive in rather diverse environmental conditions. In this study, the X-cell parasite was detected for the first time in environmental samples and, also for the first time, in a lacustrine/freshwater system. The X-cells found here were noticeably different in the genetic composition of the 18S V4 region compared to earlier observations of the X-cell, suggesting that they might constitute new clades within the X-cell lineage.

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