Both versions of the gene, sexM and sexP, encode for a single protein called a high mobility group (HMG)-domain protein that leads to sex differentiation through an unknown process. This protein is very similar to one encoded by the human Y chromosome, called SRY, that when turned on leads a developing fetus to exhibit male characteristics. Heitman said this similarity suggests that HMG-domain proteins may mark the evolutionary beginnings of sex determination in both fungi and humans.
Heitman's team proposes that sexM and sexP were once the same gene that went through a mutation process called inversion. The new versions then evolved into two separate sex genes. The same process is most likely responsible for the evolution of the male Y chromosome, Heitman suggests.
Heitman hopes to next identify the sex region in another fungus, Rhizopus oryzae in order to better understand how HMG-domain proteins control sex determination in fungi. Rhizopus' genes can be cultured and chemically altered in a way that Phycomyces' sex genes can not.
"Rhizopus can be used to understand the influences of certain genes in lesser studied fungi much in the way we use mice to understand genetic effects in humans," explained Alexander Idnurm, Ph.D., the primary author on the study and recently appointed assistant professor at the University of Missouri-Kansas City.
Another troubling mystery for Heitman is that certain younger fungal species lack HMG-domain proteins. He proposes that these proteins have been replaced with alternative transcription factors, which are proteins that turn genes on and off.
|Contact: Kelly Malcom|
Duke University Medical Center