Life-cycle-coupled evolution of mitosis in close relatives of animals.

Eukaryotes have evolved towards one of two extremes along a spectrum of strategies for remodelling the nuclear envelope during cell division: disassembling the nuclear envelope in an open mitosis or constructing an intranuclear spindle in a closed mitosis1,2. Both classes of mitotic remodelling involve key differences in the core division machinery but the evolutionary reasons for adopting a specific mechanism are unclear. Here we use an integrated comparative genomics and ultrastructural imaging approach to investigate mitotic strategies in Ichthyosporea, close relatives of animals and fungi. We show that species in this clade have diverged towards either a fungal-like closed mitosis or an animal-like open mitosis, probably to support distinct multinucleated or uninucleated states. Our results indicate that multinucleated life cycles favour the evolution of closed mitosis.

Characterization of Dermotheca sp. Infection in a midwestern state-endangered salamander (Ambystoma platineum) and a co-occurring common species (Ambystoma texanum).

Ichthyosporean parasites (order Dermocystida) can cause morbidity and mortality in amphibians, but their ecology and epidemiology remain understudied. We investigated the prevalence, gross and histologic appearance, and molecular phylogeny of a novel dermocystid in the state-endangered silvery salamander (Ambystoma platineum) and the co-occurring, non-threatened small-mouthed salamander (Ambystoma texanum) from Illinois. Silvery salamanders (N = 610) were sampled at six ephemeral wetlands from 2016 to 2018. Beginning in 2017, 1-3 mm raised, white skin nodules were identified in 24 silvery salamanders and two small-mouthed salamanders from five wetlands (prevalence = 0-11.1%). Skin biopsy histology (N = 4) was consistent with dermocystid sporangia, and necropsies (N = 3) identified infrequent hepatic sporangia. Parasitic 18S rRNA sequences (N = 5) from both salamander species were identical, and phylogenetic analysis revealed a close relationship to Dermotheca viridescens. Dermocystids were not identified in museum specimens from the same wetlands (N = 125) dating back to 1973. This is the first report of Dermotheca sp. affecting caudates in the Midwestern United States. Future research is needed to determine the effects of this pathogen on individual and population health, and to assess whether this organism poses a threat to the conservation of ambystomatid salamanders.

Comparative morphology and genealogical delimitation of cryptic species of sympatric isolates of Sphaeroforma (Ichthyosporea, Opisthokonta).

Of the ancient clades of unicellular relatives of the multicellular animals, ichthyosporea are among the easiest to collect, cultivate, and analyze at the population level. Once identified, species can be correlated with their animal hosts and geographical ranges. However, the spherical stages common to many ichthyosporea provide little basis for morphological species identification. This study of the genus Sphaeroforma is the first to apply patterns of genetic discontinuity to delimit species among any of the unicellular 'holozoa.' Sequences of three loci from 148 sympatric isolates, along with type cultures, provided concordant support for new species "Sphaeroforma nootkatensis" and "Sphaeroforma gastrica," and for formally describing 'Pseudoperkinsus tapetis,' as "Sphaeroforma tapetis". We document light and electron microscopic characters that distinguish the genus but not its species. "S. tapetis" sometimes had brief amoeboid or plasmodial motile stages and endospore release through pores. Unlike closely related Creolimax, Sphaeroforma lacked a central vacuole but had multiple peripheral nucleoli. Like distantly related eccrinales, Sphaeroforma cell walls had pores and a calyx. Analyses of allele frequencies in "S. tapetis" indicated geographical differentiation but no host specificity. Accurate molecular identification of species will increase the feasibility and reliability of further studies of Sphaeroforma in its natural habit.

Fossilized nuclei and germination structures identify Ediacaran "animal embryos" as encysting protists.

Globular fossils showing palintomic cell cleavage in the Ediacaran Doushantuo Formation, China, are widely regarded as embryos of early metazoans, although metazoan synapomorphies, tissue differentiation, and associated juveniles or adults are lacking. We demonstrate using synchrotron-based x-ray tomographic microscopy that the fossils have features incompatible with multicellular metazoan embryos. The developmental pattern is comparable with nonmetazoan holozoans, including germination stages that preclude postcleavage embryology characteristic of metazoans. We conclude that these fossils are neither animals nor embryos. They belong outside crown-group Metazoa, within total-group Holozoa (the sister clade to Fungi that includes Metazoa, Choanoflagellata, and Mesomycetozoea) or perhaps on even more distant branches in the eukaryote tree. They represent an evolutionary grade in which palintomic cleavage served the function of producing propagules for dispersion.

Ketoconazole inhibits the growth and development of Ichthyophonus sp. (Mesomycetozoa) in vitro.

We determined the in vitro effect of the azol-derivative antifungal ketoconazole (KZ) on the morphology, growth, and development of teleost fish parasite Ichthyophonus sp. The KZ was delivered to culture medium using liposomes (L) or a lipid emulsion (E) at five different doses (i.e. 5, 50, 100, 200, and 400 microg/ml) for both L and E formulations. Controls consisted of Eagle's minimum essential medium (MEM) supplemented with 10% foetal bovine serum (MEM-10) alone (C-MEM) or containing amounts of L or E equivalent to those used in the KZ100 and KZ400 treatments (i.e. 100L, 400L, 100E, and 400E, respectively). Morphological alterations, such as a decrease in the number of dividing spores and nuclei, and condensation or even destruction of the cytoplasm, were observed using light and electron microscopy in the MEM-cultured organisms receiving KZ formulations, especially with KZ400L preparations, at both 7- and 14-d postinoculation. The KZ treatments also demonstrated a statistically significant inhibition of Ichthyophonus growth in MEM. These treatments also had an inhibitory effect on subsequent Ichthyophonus germination in Earle's fish saline agar (EFSA) medium, which was more evident for L formulations when the organism was treated for 7 d and for E formulations at 14 d. Our results endorse the potential use of KZ for the treatment for ichthyophonosis and provide support to proceed to in vivo assays.