Biology subjects

Fabio Zanini

Publications and source records attributed to Fabio Zanini.

3 recordsLinked to original sources

bioRxiv2016

Error rates, PCR recombination, and sampling depth in HIV-1 Whole Genome Deep Sequencing

Deep sequencing is a powerful and cost-effective tool to characterize the genetic diversity and evolution of virus populations. While modern sequencing instruments readily cover viral genomes many thousand fold and very rare variants can in principle be detected, sequencing errors, amplification biases, and other artifacts can limit sensitivity and complicate data interpretation. Here, we describe several control experiments and error correction methods for whole-genome deep sequencing of viral genomes. We developed many of these in the course of a large scale whole genome deep sequencing study of HIV-1 populations. We measured the substitution and indel errors that arose during sequencing and PCR and quantified PCR-mediated recombination. We find that depending on the viral load in the samples, rare mutations down to 0.2% can be reproducibly detected. PCR recombination can be avoided by consistently working at low amplicon concentrations.

Genomics↗

bioRxiv2016

Establishment and stability of the latent HIV-1 DNA reservoir

HIV-1 infection currently cannot be cured because the virus persists as integrated proviral DNA in long-lived cells despite years of suppressive antiretroviral therapy (ART). To characterize establishment, turnover, and evolution of viral DNA reservoirs we deep-sequenced the p17gag region of the HIV-1 genome from samples obtained after 3-18 years of suppressive ART from 10 patients. For each of these patients, whole genome deep-sequencing data of HIV-1 RNA populations before onset of ART were available from 6-12 longitudinal plasma samples spanning 5-8 years of untreated infection. This enabled a detailed analysis of the dynamics and origin of proviral DNA during ART. A median of 14% (range 0-42%) of the p17gag DNA sequences were overtly defective due to G-to-A hypermutation. The remaining sequences were remarkably similar to previously observed RNA sequences and showed no evidence of evolution over many years of suppressive ART. Most sequences from the DNA reservoirs were very similar to viruses actively replicating in plasma (RNA sequences) shortly before start of ART. The results do not support persistent HIV-1 replication as a mechanism to maintain the HIV-1 reservoir during suppressive therapy. Rather, the data indicate that viral DNA variants are turning over as long as patients are untreated and that suppressive ART halts this turnover.

Microbiology↗

bioRxiv2016

In-vivo mutation rates and fitness landscape of HIV-1

Mutation rates and fitness costs of deleterious mutations are difficult to measure in vivo but essential for a quantitative understanding of evolution. Using whole genome deep sequencing data from longitudinal samples during untreated HIV-1 infection, we estimated mutation rates and fitness costs in HIV-1 from the temporal dynamics of genetic variation. At approximately neutral sites, mutations accumulate with a rate of 1.2 x 10-5 per site per day, in agreement with the rate measured in cell cultures. The rate from G to A is largest, followed by the other transitions C to T, T to C, and A to G, while transversions are more rare. At non-neutral sites, most mutations reduce virus replication; using a model of mutation selection balance, we estimated the fitness cost of mutations at every site in the HIV-1 genome. About half of all nonsynonymous mutations have large fitness costs (greater than 10%), while most synonymous mutations have costs below 1%. The cost of synonymous mutations is especially low in most of gag and pol, while much higher costs are observed in important RNA structures and regulatory regions. The intrapatient fitness cost estimates are consistent across multiple patients, suggesting that the deleterious part of the fitness landscape is universal and explains a large fraction of global HIV-1 group M diversity.

Evolutionary Biology↗