June 5, 2008
UNIT 6: Classification and DiversityFungus May Help Explain What Separates the Women from the Men
Fungi don’t present as females and males. They do, however, have different mating types. These mating types are not determined by entire sex chromosomes; rather, they are determined by sequences of DNA.
A group of researchers from Duke University Medical Center hypothesized that the sex-determining genes in fungi would be a sort of molecular fossil, providing clues about sex determination in other organisms, too. According to Joseph Heitman, leader of the research team, “Fungi are good model systems for the evolution of human sexual differentiation because the genetic sequences responsible for sex are smaller versions of chromosomal sex-determining regions in people.”
For their study, the research team selected one of the oldest identified types of fungus, Phycomyces blakesleeanus. They identified a stretch of DNA that appeared to be shared by many different types of fungi. Within this stretch, the researchers identified two versions of a gene that codes for a protein responsible for sex differentiation. Fungi with opposite versions of the gene are able to mate with one another.
The protein encoded by the fungal gene has a high mobility group (HMG) domain, a region of the protein that binds to DNA. The fungal protein is very similar to one encoded by the human Y chromosome. The human protein helps a developing fetus to form male characteristics. This similarity led Heitman to speculate that proteins with the HMG domain may have marked the beginning of sex determination in both fungi and humans. The researchers hope to learn more about how HMG-domain proteins control sex determination by studying the sex-determining genes of other types of fungi.