HIV is thought to have originated from chimpanzees in central Africa that were infected with simian immunodeficiency virus (SIV), a retrovirus. "If you look at the diversity present across SIV in chimpanzees, it suggests that they have had it for tens of thousands of years," Roca said.
HIV-1 Type M, which accounts for 90 percent of human infections, is believed to have crossed the species barrier into human populations between 1884 and 1924. Roca said that it may have crossed much earlier and many times, selecting for genetic resistance in isolated rural populations while remaining undetected.
"Some of the scientific literature suggests that the persistence of HIV in humans required population densities typical of the larger cities that appeared in West Central Africa during the colonial era," he said.
Perhaps an even more important factor is that, before modern medicine and vaccinations, infectious diseases such as smallpox killed large numbers of people. People with compromised immune systems may have succumbed first, preventing the immunodeficiency virus from spreading.
If HIV crossed the species barrier many times, it is possible that selection favored protective genetic variants in the affected populations. Roca and his co-investigators looked for evidence of this selection in the Biaka genomes.
The Biaka are a human community that inhabits forests in the range of the chimpanzee subspecies believed to be the source of the current HIV pandemic. The researchers compared Biaka genomes with the genomes of four other African populations who live outside the chimpanzee's range.
Biaka genotypes were available through the Human Genome Diversity Project, which collected biological samples from 52 different population groups across the world. The project genotyped these diverse human communities for single nucleotide polymorphisms (SNPs, pronounced "snips"), or genomic variation, at around 650,000 locations across the genome.
Previous research that used cell lines made in the 1980s from individuals who had AIDS or were believed to be at risk for it had identified 26 genomic locations as being involved in resistance to HIV. Kai Zhao, a graduate student working in Roca's laboratory, examined these locations.
Zhao ran all 10 possible pairwise comparisons for the five human populations and looked for selection signatures. Specifically, selection for a genetic trait tends to reduce diversity in the surrounding genomic region within the affected population, increasing the differences between populations.
The researchers looked at the genomic regions that contain genes known to have a protective effect against HIV to see if there was any overlap with the selection signatures. Eight of the comparisons found overlap. Seven involved the Biaka.
They identified four genes in these overlaps that code for proteins affecting either the ability of HIV to infect the host cell or the disease progression. The researchers also found that for several genes, SNPs associated with protection against HIV-1 were common among the Biaka.
Roca cautions that these results should not be considered definitive. It is not possible to rule out false positives.
"You may detect a signature of selection, but it doesn't necessarily mean that selection has caused it. It's just a good sign that selection may have occurred," he said. Also, the signature of selection may span several genes, of which only one is actually protective against HIV-1.
However, he said that the results are intriguing and indicate that this line of research is worth pursuing.
"If additional studies confirm that these genes have undergone selection and that human populations in the region have some genetic resistance to HIV-1, one could try to find additional genes in the population that may also be protective against HIV but have not yet been identified," he said.
"The mechanism by which these genes work could be determined," he continued. "It could open up a new line of research for fighting retroviruses."
"Evidence for selection at HIV host susceptibility genes in a West Central African human populations" by Kai Zhao, Yasuko Ishida, Taras K. Oleksyk, and Alfred A. Roca has been recently published in BMC Evolutionary Biology. It is available online at http://www.biomedcentral.com/1471-2148/12/237/abstract.
This research was supported by the Bill and Melinda Gates Foundation Grand Challenges Exploration Initiative.
Susan Jongeneel | EurekAlert!
Rainbow colors reveal cell history: Uncovering β-cell heterogeneity
22.09.2017 | DFG-Forschungszentrum für Regenerative Therapien TU Dresden
The pyrenoid is a carbon-fixing liquid droplet
22.09.2017 | Max-Planck-Institut für Biochemie
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
22.09.2017 | Life Sciences
22.09.2017 | Medical Engineering
22.09.2017 | Physics and Astronomy