Two New Species of Marine Saprotrophic Sphaeroformids in the Mesomycetozoea Isolated From the Sub-Arctic Bering Sea

Hassett, Brandon T.; López, J. Andrés; Gradinger, Rolf

doi:10.1016/j.protis.2015.04.004

Cited by 15 publications

(17 citation statements)

References 12 publications

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“…S. arctica cells were cultured at 12°C in Difco marine broth (MB) medium. Although pseudopodial cells and cells with large vacuoles have been observed in other closely related Sphaeroforma species [ 13 ], the majority of S. arctica cells grown in these conditions exhibit uniformly round morphology, no large vacuoles, and uniformly distributed nuclei within the multinucleate coenocyte ( Figure 1 B), which suggests a simple, linear coenocytic life cycle ( Figure 1 C). Small, newborn cells grow into a multinucleate coenocyte by rounds of synchronous nuclear divisions [ 9 ] followed by cellularization and release of the daughter cells (burst).…”

Section: Resultsmentioning

confidence: 79%

Decoupling of Nuclear Division Cycles and Cell Size during the Coenocytic Growth of the Ichthyosporean Sphaeroforma arctica

2018

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SummaryCoordination of the cell division cycle with the growth of the cell is critical to achieve cell size homeostasis [1]. Mechanisms coupling the cell division cycle with cell growth have been described across diverse eukaryotic taxa [2, 3, 4], but little is known about how these processes are coordinated in organisms that undergo more complex life cycles, such as coenocytic growth. Coenocytes (multinucleate cells formed by sequential nuclear divisions without cytokinesis) are commonly found across the eukaryotic kingdom, including in animal and plant tissues and several lineages of unicellular eukaryotes [5]. Among the organisms that form coenocytes are ichthyosporeans, a lineage of unicellular holozoans that are of significant interest due to their phylogenetic placement as one of the closest relatives of animals [6]. Here, we characterize the coenocytic cell division cycle in the ichthyosporean Sphaeroforma arctica. We observe that, in laboratory conditions, S. arctica cells undergo a uniform and easily synchronizable coenocytic cell cycle, reaching up to 128 nuclei per cell before cellularization and release of daughter cells. Cycles of nuclear division occur synchronously within the coenocyte and in regular time intervals (11–12 hr). We find that the growth of cell volume is dependent on concentration of nutrients in the media; in contrast, the rate of nuclear division cycles is constant over a range of nutrient concentrations. Together, the results suggest that nuclear division cycles in the coenocytic growth of S. arctica are driven by a timer, which ensures periodic and synchronous nuclear cycles independent of the cell size and growth.

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Section: Resultsmentioning

confidence: 79%

Decoupling of Nuclear Division Cycles and Cell Size during the Coenocytic Growth of the Ichthyosporean Sphaeroforma arctica

2018

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“…Although, it could be possible that miRNAs were not detected in C. fragrantissima because their expression is restricted to certain developmental time points not present under our culture conditions. The existence of such stages have been suggested for closely related Sphaeroforma species [ 34 ] and could as well exist in C. fragrantissima . Drosha has also been found to cleave other types of secondary RNA stem-loop structures in mouse cell lines [ 35 ], which could represent an alternative function for the Drosha homolog in C. fragrantissima .…”

Section: Resultsmentioning

confidence: 99%

“… This paper ENA: PRJEB21207 Experimental Models: Organisms/Strains Sphaeroforma arctica Iñaki Ruiz-Trillo’s lab. Original reference [ 40 ] Strain JP610 Sphaeroforma sirkka Brandon Hassett [ 34 ] Strain B5 Sphaeroforma napiecek Brandon Hassett [ 34 ] Strain B4 Capsaspora owczarzaki ATCC nr. 30864 N/A Creolimax fragrantissima Iñaki Ruiz-Trillo’s lab (available from ATCC nr.…”

Section: Methodsmentioning

confidence: 99%

Unicellular Origin of the Animal MicroRNA Machinery

et al. 2018

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SummaryThe 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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“…), as previously described (Hassett et al. ). PCR products were purified using the PureLink Quick PCR Purification Kit (Thermo Fisher Scientific) and Sanger sequenced bidirectionally to maximize confidence in base calls along the length of the amplicon.…”

Section: Methodsmentioning

confidence: 99%

“…Genomic DNA was isolated from 14-d cell cultures using the DNeasy PowerSoil Kit (Qiagen, Hilden, Germany) following the manufacturer's protocol. Genomic DNA was amplified using polymerase chain reaction (PCR) with Platinum Taq (Thermo Fisher Scientific, Waltham, MA) and the 18S rRNA NS1/NS4 (5 0 -GTAGTCATATGCTTGTCTC-3 0 / 5 0 -CTTCCGTCAATTCCTTTAAG-3 0 ) and NS5/NS8 (5 0 -AACT TAAAGGAATTGACGGAAG-3 0 /5 0 -TCCGCAGGTTCACCTACG GA-3 0 ) primer pairs (White et al 1990), as previously described (Hassett et al 2015). PCR products were purified using the PureLink Quick PCR Purification Kit (Thermo Fisher Scientific) and Sanger sequenced bidirectionally to maximize confidence in base calls along the length of the amplicon.…”

Section: Dna Extraction Amplification and Sequencingmentioning

confidence: 99%

New Species of Saprobic Labyrinthulea (=Labyrinthulomycota) and the Erection of a gen. nov. to Resolve Molecular Polyphyly within the Aplanochytrids

Hassett¹,

Gradinger²

2018

J Eukaryotic Microbiology

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A culture of a unicellular heterotrophic eukaryote was established from pollen-baited seawater acquired from the nearshore environment in Tromsø, Norway. Light microscopy revealed the production of ectoplasmic nets and reproduction by biflagellated zoospores, as well as binary division. After culturing and subsequent nucleotide extraction, database queries of the isolate's 18S small ribosomal subunit coding region identified closest molecular affinity to Aplanochytrium haliotidis, a pathogen of abalone. Testing of phylogenetic hypotheses consistently grouped our unknown isolate and A. haliotidis among the homoplasious thraustochytrids. Transmission electron microscopy revealed complex cell walls comprised of electron-dense lamella that formed protuberances, some associated with bothrosomes. Co-culturing experiments with the marine fungus Penicillium brevicompactum revealed prolonged interactions with hyphal strands. Based on the combined information acquired from electron microscopy, life history information, and phylogenetic testing, we describe our unknown isolate as a novel species. To resolve molecular polyphyly within the aplanochytrids, we erect a gen. nov. that circumscribes our novel isolate and the former A. haliotidis within the thraustochytrids.

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Two New Species of Marine Saprotrophic Sphaeroformids in the Mesomycetozoea Isolated From the Sub-Arctic Bering Sea

Cited by 15 publications

References 12 publications

Decoupling of Nuclear Division Cycles and Cell Size during the Coenocytic Growth of the Ichthyosporean Sphaeroforma arctica

Decoupling of Nuclear Division Cycles and Cell Size during the Coenocytic Growth of the Ichthyosporean Sphaeroforma arctica

Unicellular Origin of the Animal MicroRNA Machinery

New Species of Saprobic Labyrinthulea (=Labyrinthulomycota) and the Erection of a gen. nov. to Resolve Molecular Polyphyly within the Aplanochytrids

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