Biologically speaking, nearly every species on Earth has two opposite sexes, male and female. But with some fungi and other microbes, sex can be a lot more complicated. Some members of Cryptococcus, a family of fungus linked to human disease, can have tens of thousands of different mating types. – Duke University.
In a study appearing early online Aug. 11 in PLOS Biology, Duke researchers have mapped the evolutionary turning point that transformed the pathogenic form of Cryptococcus from an organism of many sexes to one with only two. They found that during evolution, a reshuffling of DNA known as translocation brought together separate chunks of sex-determining genes onto a single chromosome, essentially mimicking the human X or Y chromosome. – Duke University.
Surprisingly, they’ve shown that these crucial translocations occurred at the centromeres, the twisty ties that hold together chromosomes at the center of an x-shaped pair. These regions of the chromosome are so dense that they were once thought to be removed from recombination. –Duke University.
“Recombination at the centromere doesn’t need to happen every now and again, it simply needs to happen frequently enough that it accentuates the development of the living being,” said Joseph Heitman, MD, PhD, senior investigation creator and teacher and seat of sub-atomic hereditary qualities and microbiology at Duke University School of Medicine. “With every translocation, the genome is adjusted over and over, until the point when you have advanced a totally new species.”
Researchers have been examining the advancement of sex chromosomes for over a century. In the 1960’s, Japanese-American geneticist and developmental researcher Susumu Ohno proposed a hypothesis in which the qualities deciding sex initially emerged at different spots scattered over the whole genome, yet after some time were “caught” on the sex chromosomes. In people, those chromosomes pass by the well-known X and Y; in winged animals, they are known as Z and W; in greenery, they are called U and V.
Despite the name or species, Heitman fights that some all inclusive standards could oversee the advancement of all sex chromosomes. He and a universal group of scientists concentrated on the last basic progenitor of the human pathogen Cryptococcus neoformans and its closest kin species, a non-pathogen called Cryptococcus amylolentus.
In C. amylolentus, many qualities at two unique areas on the chromosomes control what’s known as a tetrapolar, or four-section, mating framework. At one area or locus known as P/R, qualities encode pheromones and pheromone receptors that assistance the growth perceive perfect mating sorts. At alternate locus, called HD, qualities oversee the advancement of sexual structures and regenerative spores.
The scientists sequenced the whole genome of C. amylolentus, mapping the area of the considerable number of qualities and also the centromeres on each of the creature’s 14 chromosomes.
They found that the genomes had experienced a considerable amount of modification since the two species shared a typical precursor, no less than 50 million years back. For instance, chromosome 1 of C. neoformans contained bits of four unique chromosomes from C. amylolentus, giving confirmation of various translocations, some inside the centromere.
“That was extremely amazing. The doctrine has been that recombination is stifled in centromeric locales,” said Sheng Sun, PhD, lead think about creator and associate research educator at Duke University School of Medicine.
In the 1980’s, a fundamental paper by Duke partner Tom Petes showed recombination could happen over the centromeres in Saccharomyces cerevisiae, however some ascribed the finding to an idiosyncrasy of the favored model life form with its little point centromeres. Be that as it may, from that point forward, different examinations have risen proposing that the marvel was more extensive spread.
In this examination, the scientists demonstrated that in Cryptococcus amylolentus, the hereditary express, the P/R locus lived on chromosome 10 and the HD locus on chromosome 11. Be that as it may, in Cryptococcus neoformans, the advanced express, those loci wound up in one place. As indicated by their model, numerous translocations stored the two sex determinants on a similar chromosome, with a centromere in the middle. Resulting modifications put P/R and HD by each other. The outcome was a life form with a bipolar mating framework, much like the male and female genders that encapsulate generally species.
“In any sort of model this way, you are considering what could have been the association in the last normal precursor, which is currently terminated so you can’t know completely,” said Heitman. “In any case, in each of these genealogies, there are various developmental occasions that have happened, and you can utilize genomics to turn back the hands of time and derive the direction.”
Heitman says their investigation recommends that different specialists ought to effectively search for translocations, both in the normal areas and additionally inside centromeres. These chromosomal modifications are a typical reason for birth imperfections and tumor in people.
He and his partners are right now examining whether comparable translocations happen in the advancement of sex chromosomes in other parasitic families, for example, Ustilago and Malassezia.
The investigation was a worldwide community oriented exertion, including key commitments from Vikas Yadav and Kaustuv Sanyal at the Jawarharlal Nehru Center for Advanced Scientific Research in Bangalore, India; Christina Cuomo at the Broad Institute in Cambridge, Massachusetts; Minou Nowrousian at Ruhr University in Bochum, Germany; Teun Boekhout at CBS in the Netherlands; and Jean-Luc Souciet, Betina Porcel and Patrick Wincker at Genoscope in France.