The salmon of the Baltic reach maturity younger and younger. Because of this they return to their home rivers smaller than before. The reason is still a mystery but the key seems to be the gene VGLL3. Understanding it may explain the questions of human puberty as well.

Ten thousand salmon eggs. This will be the dowry that Craig Primmer, professor of genetics, intends to bring with him to the Viikki Campus this autumn.

And it’s not just any old roe, the eggs will be for varieties of salmon specifically bred for research. The gene VGLL3 plays a crucial role. In 2015, Primmer and his Norwegian colleagues proved that it regulates the age at which a salmon reaches sexual maturity.

 “VGLL3 is a regulating gene, which tells other genes to switch on and off. By creating several varieties with different versions of VGLL3 in a controlled environment, we will be able to monitor how great the gene’s significance really is,” Primmer explains.

At the beginning of 2018, the salmon will be moved to the Lammi Biological Station into facilities specifically built for them. The intention is to study them in salmon farms where the food and water temperature can be controlled. This stage will take from two to three years.

Studying salmon puberty is interesting, because it has such a clear impact on the lifespan of the salmon.

Salmon migrate from their home rivers to live in the ocean from one to five years, until puberty brings them back to the rivers.

The ideal age of sexual maturity is lower for male salmon than it is for females. It’s enough for a male to have the strength to swim up the river to mate, but a female must also be able to build a rock enclosure for the eggs to protect them from the current.

During the past few years, salmon have started to reach puberty earlier on average. The reason for this is unknown, but Primmer’s research may shed some light on the issue.

Why spend years and millions of euros to determine the age of puberty in salmon?

 “First of all, this is basic research. I’m a geneticist, so I am primarily interested in how genes cause changes in populations in the wild. The salmon is a very interesting case in this sense, as it has several varieties that differ slightly from one another,” says Primmer.

The research may also be useful in practice. Farmed salmon typically reach puberty early and do not grow as large as the producers hope. Research can help determine why this happens.

And as is often the case with basic research, this work can also yield unexpected applications. In 2014, it was established that the same VGLL3 gene exists in both humans and salmon. Last year, a study indicated that the gene may have an impact on certain gender-specific immunological diseases.

Primmer was surprised.

 “I would never have guessed that we would be cited in a medical paper.”