The mycobiome of Australian tree hollows in relation to the Cryptococcus gattii and C. neoformans species complexes

Cryptococcosis is a fungal infection caused by members of the Cryptococcus gattii and C. neoformans species complexes. The C. gattii species complex has a strong environmental association with eucalypt hollows (particularly Eucalyptus camaldulensis), which may present a source of infection. It remains unclear whether a specific mycobiome is required to support its environmental survival and growth. Conventional detection of environmental Cryptococcus spp. involves culture on differential media, such as Guizotia abyssinica seed agar. Next‐generation sequencing (NGS)‐based culture‐independent identification aids in contextualising these species in the environmental mycobiome. Samples from 23 Australian tree hollows were subjected to both culture‐ and amplicon‐based metagenomic analysis to characterize the mycobiome and assess relationships between Cryptococcus spp. and other fungal taxa. The most abundant genera detected were Coniochaeta, Aspergillus, and Penicillium, all being commonly isolated from decaying wood. There was no correlation between the presence of Cryptococcus spp. in a tree hollow and the presence of any other fungal genus. Some differences in the abundance of numerous taxa were noted in a differential heat tree comparing samples with or without Cryptococcus‐NGS reads. The study expanded the known environmental niche of the C. gattii and C. neoformans species complexes in Australia with detections from a further five tree species. Discrepancies between the detection of Cryptococcus spp. using culture or NGS suggest that neither is superior per se and that, rather, these methodologies are complementary. The inherent biases of amplicon‐based metagenomics require cautious interpretation of data through consideration of its biological relevance.     

Metabolic profile and quantification of deoxyribose synthesis pathways in HepG2 cells

Traditional tracer studies of cell proliferation fail to distinguish between label enrichment due to increased DNA repair versus DNA replication. We used the emerging stable (non-radiating) isotope-based dynamic metabolic profiling technique on HepG2 cells to determine synthesis pathways of nucleic acids from glucose and rates of proliferation using CG-MS assay of RNA and DNA enrichment. Comparing the isotopic enrichment curve in DNA with the theoretical curve based on cell growth, we observed that the measured tracer enrichment was significantly higher, indicating that surplus label was acquired during DNA repair. In particular, after the first duplication (3 days), 80.13% of the total enrichment observed corresponds to duplication and 19.87% corresponds to DNA repair as calculated from the [1, 2-¹³C₂]-glucose incorporation curve. Our data indicate contemporary measurements of cell proliferation rates relying on tracer incorporation may be overestimated. ¹³C label was distributed between m1 (m1/Σm = 80) and m2 (m2/Σm = 14) of deoxyribose, indicating that most of the glucose carbon was acquired via direct glucose oxidation in the pentose cycle. The stable isotope technique distinguishes rates of DNA synthesis and repair via the oxidative and non-oxidative pentose cycle, separately, in one test, without inhibition of either process. The contribution of DNA repair in malignant cells to isotope accumulation in deoxyribose remains to be investigated.     

Fungal transformation of natural and synthetic cobalt-bearing manganese oxides and implications for cobalt biogeochemistry

Manganese oxide minerals can become enriched in a variety of metals through adsorption and redox processes, and this forms the basis for a close geochemical relationship between Mn oxide phases and Co. Since oxalate-producing fungi can effect geochemical transformation of Mn oxides, an understanding of the fate of Co during such processes could provide new insights on the geochemical behaviour of Co. In this work, the transformation of Mn oxides by Aspergillus niger was investigated using a Co-bearing manganiferous laterite, and a synthetic Co-doped birnessite. A. niger could transform laterite in both fragmented and powder forms, resulting in formation of biomineral crusts that were composed of Mn oxalates hosting Co, Ni and, in transformed laterite fragments, Mg. Total transformation of Co-doped birnessite resulted in precipitation of Co-bearing Mn oxalate. Fungal transformation of the Mn oxide phases included Mn(III,IV) reduction by oxalate, and may also have involved reduction of Co(III) to Co(II). These findings demonstrate that oxalate-producing fungi can influence Co speciation in Mn oxides, with implications for other hosted metals including Al and Fe. This work also provides further understanding of the roles of fungi as geoactive agents which can inform potential applications in metal bioremediation, recycling and biorecovery.     

The role of the calcium-sensing receptor in epidermal differentiation

Calcium regulates the proliferation and differentiation of keratinocytes both in vivo and in vitro. Elevated extracellular Ca2+ concentration ([Ca2+]o) raises the intracellular free calcium ([Ca2+]i) and activates differentiation-related genes. Cells lacking the calcium-sensing receptor (CaR) fail to respond to [Ca2+]o and to differentiate, indicating a role for CaR in keratinocyte differentiation. These concepts derived from in vitro experiments have been tested and confirmed in two mouse models.     

Recognition of lumenal prion protein aggregates by post-ER quality control mechanisms is mediated by the preoctarepeat region of PrP

Prion diseases are fatal transmissible neurodegenerative disorders linked to an aberrant conformation of the cellular prion protein (PrP(c)). We have shown previously that the chemical compound suramin induced aggregation of fully matured PrP(c) in post-ER compartments, thereby, activating a post-ER quality control mechanism and preventing cell surface localization of PrP by intracellular re-routing of aggregated PrP from the Golgi/TGN directly to lysosomes. Of note, drug-induced PrP aggregates were not toxic and could easily be degraded by neuronal cells. Here, we focused on determining the PrP domains mediating these effects. Using PrP deletion mutants we show that intracellular re-routing but not aggregation depends on the N-terminal PrP (aa 23-90) and, more precisely, on the preoctarepeat domain (aa 23-50). Fusion of the PrP N-terminus to the GPI-anchored protein Thy-1 did not cause aggregation or re-routing of the chimeric protein, indicating that the N-terminus is only active in re-routing when prion protein aggregation occurs. Insertion of a region with a comparable primary structure contained in the PrP paralogue prnd/doppel (aa 27-50) into N-terminally deleted PrP re-established the re-routing phenotype. Our data reveal an important role for the conserved preoctarepeat region of PrP, namely controlling the intracellular trafficking of misfolded PrP.     

Hürthle cell carcinoma: diagnostic and therapeutic implications

Background  

Hürthle cell carcinoma is a variant of follicular cell carcinoma of thyroid. It may present as a low-grade tumour or as a more aggressive type. Prognosis depends upon the age of the patient, tumour size, extent of invasion and initial nodal or distant metastasis.