New Sex Hormone Discovered: Secretoneurin
A large protein called secretogranin-2 is important for the normal functioning of brain cells and other cells that secrete hormones to control body functions such as growth and reproduction. However, secretogranin-2 can get chopped up by special enzymes and an international team of researchers found that one small fragment called secretoneurin is important for stimulating sexual function in the zebrafish (Danio rerio).
Zebrafish are freshwater fish belonging to the carp and minnow family that are now a widely used model organism in biomedical research.
Using gene editing technology, University of Ottawa biologist Kim Mitchell and colleagues changed secretogranin-2 genes through specific mutation and found that it affected the ability of female and male zebrafish to breed.
It severely reduced their sexual behavior. The fish look normal, but when both sexes are put together, they almost ignore each other.
“Normally, within a few minutes after a male and female are introduced for the first time, the male chases the female in a courtship ritual, and shortly therefore they spawn — that is to say, the female releases her eggs to the water, and the male instantly fertilizes them,” the scientists said.
“But we found that only 1 in 10 of the couples with mutated genes could spawn.”
“The couples carrying the introduced mutations produce eggs and sperm, but they are simply terrible at mating with each other.”
“This is the first evidence that mutation of these genes leads to disruption of sexual behavior in any animal.”
In the genetically altered fish, the researchers can partially restore sexual function by a single injection of secretoneurin into the body.
They believe the peptide acts on cells in the brain and pituitary gland to increase hormone release thereby enhancing the ability of the female to ovulate and lay her eggs.
“The secretoneurin produced in fish is remarkably similar to that found in other animals, including humans,” they said.
“We can now use our genetically modified fish to look for other factors that could enhance sexual function, be it for increased spawning in cultured fish species, or to help with the search for new human infertility treatments.”
“This is just the beginning of the possibilities. The large secretogranin-2 genes may produce many other hormone-like peptides with unknown functions. It will be exciting to explore this in future research projects.”
A paper on the findings will be published in the Proceedings of the National Academy of Sciences.
Kimberly Mitchell el al. 2020. Targeted mutation of secretogranin-2 disrupts sexual behavior and reproduction in zebrafish. PNAS, in press; doi: 10.1073/pnas.2002004117