Biology subjects

Yakass, M. B.

Publications and source records attributed to Yakass, M. B..

4 recordsLinked to original sources

bioRxiv2024

Thymidine kinase-expressing yellow fever 17D reporter virus facilitates prodrug activation and bioorthogonal labelling of infected cells

Tracking of viral replication and tissue tropism by in vivo imaging can help to unveil how live-attenuated vaccines such as the yellow fever 17D (17D) work, and likewise, to understand how adverse effects develop. Here we validate 17D-TK, a reporter virus derived from 17D that expresses herpes virus thymidine kinase (TK) that specifically converts nucleoside analogues such as Ganciclovir (GCV) to induce cell death, or difluoro-EdU (dF-EdU) for bioorthogonal labelling of infected cells by Click chemistry. 17D-TK induces a cytopathic effect in infected cell cultures, as well as mortality in intracranially inoculated mouse pups in a GCV dependent manner. Preferential phosphorylation of difluoro-EdU (dF-EdU) in 17D-TK infected cells allows to selectively stain cells that support 17D replication. Prospectively, 17D-TK can be used in combination with radiolabeled tracers for real-time detection and localization of sites of active viral replication in living animals using positron emission tomography (PET).

microbiology↗

bioRxiv2024

De novo rates of a Trypanosoma-resistant mutation in two human populations

Until recently, mutation rates have only been measured as averages across many genomic positions. Recently, a method to measure mutation rates at the single-mutation resolution was applied to a narrow region in the human hemoglobin subunit beta (HBB) gene containing the site of the hemoglobin S (HbS) mutation as well as to a paralogous hemoglobin subunit delta (HBD) region, in sperm samples from sub-Saharan African and northern European donors. The HbS mutation, which protects against malaria while causing sickle-cell anemia in homozygotes originated de novo significantly more frequently in the HBB gene in Africans compared to the other three test cases combined (the European HBB gene and the European and African HBD gene). Here, we apply this approach to the human apolipopro-tein L1 (APOL1) gene containing the site of the G1 1024A[->]G mutation, which protects against African sleeping sickness caused by Trypanosoma brucei gambiense while causing a substantially increased risk of chronic kidney disease (CKD) in homozygotes. We find that the 1024A[->]G mutation is the mutation of highest de novo origination rate and deviates most from the genome-wide average rate for its type (A[->]G) compared to all other observable mutations in the region, and that it originates de novo significantly more frequently in Africans than in Europeans--i.e., in the population where it is of adaptive significance. The results are inconsistent with the notion that the probability of a specific mutational event is independent of its value to the organism and underscore the importance of studying mutation rates at the single-mutation resolution.

evolutionary biology↗

bioRxiv2022

Biodistribution and Environmental Safety of a Live-attenuated YF17D-vectored SARS-CoV-2 Vaccine Candidate

New platforms are urgently needed for the design of novel prophylactic vaccines and advanced immune therapies. Live-attenuated yellow fever vaccine YF17D serves as vector for several licensed vaccines and platform for novel vaccine candidates. Based on YF17D, we developed YF-S0 as exceptionally potent COVID-19 vaccine candidate. However, use of such live RNA virus vaccines raises safety concerns, i.e., adverse events linked to original YF17D (yellow fever vaccine-associated neurotropic; YEL-AND, and viscerotropic disease; YEL-AVD). In this study, we investigated the biodistribution and shedding of YF-S0 in hamsters. Likewise, we introduced hamsters deficient in STAT2 signaling as new preclinical model of YEL-AND/AVD. Compared to parental YF17D, YF-S0 showed an improved safety with limited dissemination to brain and visceral tissues, absent or low viremia, and no shedding of infectious virus. Considering yellow fever virus is transmitted by Aedes mosquitoes, any inadvertent exposure to the live recombinant vector via mosquito bites is to be excluded. The transmission risk of YF-S0 was hence evaluated in comparison to readily transmitting YFV-Asibi strain and non-transmitting YF17D vaccine, with no evidence for productive infection of vector mosquitoes. The overall favorable safety profile of YF-S0 is expected to translate to other novel vaccines that are based on the same YF17D platform.

microbiology↗

bioRxiv2021

De novo mutation rates at the single-mutation resolution in a human HBB gene-region associated with adaptation and genetic disease

While it is known that the mutation rate varies across the genome, previous estimates were based on averaging across various numbers of positions. Here we describe a method to measure the origination rates of target mutations at target base positions and apply it to a 6-bp region in the human {beta}-globin (HBB) gene and to the identical, homologous{delta} -globin (HBD) region in sperm cells from both African and European donors. The HBB region of interest (ROI) includes the site of the hemoglobin S (HbS) mutation, which protects against malaria, is common in Africa and has served as a classic example of adaptation by random mutation and natural selection. We found a significant correspondence between de novo mutation rates and past observations of alleles in carriers, showing that mutation rates vary substantially in a mutation-specific manner that contributes to the site frequency spectrum. We also found that the overall point mutation rate is significantly higher in Africans than Europeans in the HBB region studied. Finally, the rate of the 20A[->]T mutation, called the "HbS mutation" when it appears in HBB, is significantly higher than expected from the genome-wide average for this mutation type. Nine instances were observed in the African HBB ROI, where it is of adaptive significance, representing at least three independent originations, and no instances were observed in the European HBB ROI or in the European or African HBD ROI. Further studies will be needed to examine de novo mutation rates at the single-mutation resolution across these and other loci and organisms and to uncover the molecular mechanisms responsible.

evolutionary biology↗