Whole genome sequencing of spermatocytic tumours

Speaker: Anne Goriely
Department: Josephine Nefkens Institute
Subject: Whole genome sequencing of spermatocytic tumours
Location: Erasmus MC
Date: 28-06-2017
Author: Renée van der Winden

Anne Goriely came to talk to us about her work on spermatocytic tumours. In her talk she first gave a lot of background information before going into detail about her latest findings. She started by giving us some information on spermatocytic tumours. These testicular tumours are very rare and mostly occur in older men. They are slow growing, but can become extremely large (3-30 cm in diameter). Luckily, the prognosis is usually very good. The cell of origin for these tumours is an adult spermatogonia. This is interesting, since the germline usually does not mutate because that is evolutionarily very disadvantageous. These mutations occur through a copy error during stem cell division and the mutation rate increases with age, which explains why these tumours are usually found in older men.

Seminar 7
Mutations found in relation to age (Goriely et al., 2017)

Next, Goriely brought up Apert syndrome. This disorder only has a paternal origin and the mutation causing it is spontaneous, which means it has to have occurred during spermatogenesis. It was found that the higher the age of the father, the more likely it was that the offspring would have the disorder. This is called the paternal age effect. Apert syndrome shares this feature with other disorders. It also turns out that only gain-of-function mutations are enriched with age. This can be beneficial for the current generation, but harmful for the next. That is why they are called ‘selfish mutations’.

Goriely’s lab searched for these selfish mutations in testis. To do so they made slices of testis and stained them. They found that there was a higher level of staining in some testicular tubes, which indicated mutated spermatogonia. These selfish clones can spread over large areas of the testis and different clones can be found in the same testis. It is even possible for mutated and non-mutated clones to be side by side in a tube. Some of these mutations are strong and thus lead to impaired spermatogenesis, but this is not the case for all mutations. It turns out that these selfish clones are more numerous with increasing age and that all men have them. In that sense they can be compared to moles on the skin.

Lastly, Goriely pointed out that when a distribution was made of the occurrence of spermatocytic tumours versus age, it turned out to be bimodal. Moreover, spermatocytic tumours are rare, while selfish mutations are common. This led to the belief that there might be a second source for these tumours. At this point whole genome sequencing was used to determine that aneuploidy occurs in the testis. Hypotheses connected to this finding are that aneuploidy comes before the selfish mutation and thus they might be passenger mutations. Thus aneuploidy might drive tumorigenesis. Moreover, aneuploidy can cause a gene imbalance, causing meiosis to fail so that the cell re-enters mitosis. This can lead to the giant tumours observed.

I thought this seminar was very easy to follow due to all the background information given. I liked the topic of the talk, but I do feel that for a large part of the talk we kept coming back to the same conclusion: that mutation rate goes up with age. I would be interested to see if the hypotheses given are true and what might then be done to help treatment of these tumours.