Biology subjects

Klaassen, H.

Publications and source records attributed to Klaassen, H..

4 recordsLinked to original sources

bioRxiv2025

Surveillance of migratory shorebirds and seabirds in 2024 in Australia reveals incursions of a diversity of low pathogenicity avian influenza viruses, but not high pathogenicity avian influenza H5N1

The current panzootic of high pathogenicity avian influenza (HPAI) H5N1 has been catastrophic for wildlife, and following a significant sweep, clade 2.3.4.4b is found in every region aside from Oceania. Herein, we report the results of our third year of targeted surveillance of incoming migratory seabirds and shorebirds into Australia. We did not find evidence of HPAI H5N1 in any of the birds tested, and there were no reports of HPAI H5N1 in wildlife tested through other surveillance schemes in 2024. Unlike previous years, we detected a diversity of low pathogenicity avian influenza (LPAI) viruses in shorebirds. Through phylogenetic analysis we revealed that the H3N7 and H4N7 viruses recovered from Red-necked Stints were complex mosaic viruses, comprising segments of Eurasian, Australian shorebird, and Australian waterfowl segments. A H1N7 virus detected comprised a wholly Eurasian introduction, confirming this route for avian influenza viruses into Australian ecosystems. These results provide further evidence for the key role of long-distance migratory shorebirds in introducing novel LPAI viruses into Oceania. While our focus on northern migration routes remained appropriate for HPAI H5N1 surveillance in 2024, the continued spread of HPAI H5N1 to sub-Antarctic Islands demands consideration of a potential southern incursion route for Oceania in future.

microbiology↗

bioRxiv2024

Long distance avian migrants fail to bring 2.3.4.4b HPAI H5N1 into Australia for a second year in a row

There is an ongoing and profound burden of lineage 2.3.4.4b high pathogenicity avian influenza (HPAI) H5N1 on wildlife and poultry, globally. Herein we report the continued absence of HPAI and antibodies against lineage 2.3.4.4b HPAI from October - December 2023, in migratory birds shortly after their arrival in Australia. Given the ever-changing phenotype of this virus, worldwide studies on the occurrence, or here absence of the virus, are of critical importance to understand the virus dispersal and incursion risk and development of response strategies.

microbiology↗

bioRxiv2023

HDAC inhibitors rescue MeCP2T158M speckles in a high content screen

Rett syndrome (OMIM 312750) is a rare neurodevelopmental disorder caused by de novo mutations in the Methyl-CpG Binding Protein 2 (MeCP2) gene located on the X-Chromosome, typically affecting girls. Currently, available therapy for Rett Syndrome is only symptomatic. Rett syndrome symptoms first appear between 6 to 18 months of age, characterized by microcephaly and lack of motor coordination being the most prevalent. The disease continues to progress until adulthood when it reaches a stationary phase. More than 800 different mutations causing Rett syndrome have been described, yet the most common is T158M (9% prevalence), located in the Methyl-Binding domain (MBD) of MeCP2. Due to its importance for DNA binding through recognition of methylated CpG, mutations in the MBD have a significant impact on the stability and function of MeCP2. MeCP2 is a nuclear protein and accumulates in liquid-liquid phase condensates visualized as speckles in NIH3T3 by microscopy. We developed a high content phenotypic assay, detecting fluorescent MeCP2 speckles in NIH3T3 cells. The assay allows to identify small molecules that stabilize MeCP2-T158M and phenotypically rescue speckle formation. To validate the assay, a collection of 3572 drugs was screened, including FDA-approved drugs, compounds in clinical trials and biologically annotated tool compounds. 18 hits were identified showing at least 25% of rescue of speckles in the mutant cell line while not affecting wild-type MeCP2 speckles. Primary hits were confirmed in a dose response assay and in a thermal shift assay with recombinant MeCP2. One class of identified hits represents histone deacetylase inhibitors (HDACis) showing 25% speckle rescue of mutant MeCP2 without toxicity. This screening strategycan be expanded to additional compound libraries and support novel drug discovery.

cell biology↗

bioRxiv2020

Small-molecule antibiotic inhibitors of post-translational protein secretion

The increasing problem of bacterial resistance to antibiotics underscores the urgent need for new antibacterials. The Sec preprotein export pathway is an attractive potential alternative target. It is essential for bacterial viability and includes components that are absent from eukaryotes. Here we used a new high throughput in vivo screen based on the secretion and activity of alkaline phosphatase (PhoA), a Sec-dependent secreted enzyme that becomes active in the periplasm. The assay was optimized for a luminescence-based substrate and was used to screen a ~240K small molecule compound library. After hit confirmation and analoging, fourteen HTS secretion inhibitors (HSI), belonging to 8 structural classes, were identified (IC50 <60 M). The inhibitors were also evaluated as antibacterials against 19 Gram- and Gram+ bacterial species (including those from the WHO top pathogens list). Seven of them, HSI#6, 9; HSI#1, 5, 10 and HSI#12, 14 representing three structural families were microbicidals. HSI#6 was the most potent (IC50 of 0.4-8.7 M), against 13 species of both Gram- and Gram+ bacteria. HSI#1, 5, 9 and 10 inhibited viability of Gram+ bacteria with IC50 ~6.9-77.8 M. HSI#9, 12 and 14 inhibited viability of E. coli strains with IC50 <65 M. Moreover, HSI#1, 5 and 10 inhibited viability of an E. coli strain missing TolC to improve permeability with IC50 4-14 M, indicating their inability to penetrate the outer membrane. In vitro assays revealed that antimicrobial activity was not related to inhibition of the SecA component of the translocase and hence HSI molecules may target new unknown components that affect secretion. The results provide proof of principle for our approach, and new starting compounds for optimization.

microbiology↗