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Mutations causing infertility in Tonne-Kalscheuer syndrome identified with CRISPR

A new study has used CRISPR gene editing to identify mutations causing infertility in Tonne-Kalscheuer syndrome, a rare developmental disorder.

Researchers from the University of Dundee identified how an enzyme supports the proper development of mouse reproductive cells important for fertility. They propose that RNF12 performs a key role in reproductive development and should be a candidate for future study.

The new findings, published in Science Signalling, could inform research into certain human developmental disorders.

“This work in mouse stem cells yields clues about why genetic mutations can cause infertility in patients with developmental disorders”, the authors noted.

Understanding Tonne-Kalscheuer syndrome

One such developmental disorder is Tonne-Kalscheuer syndrome. This is a rare and recently identified X-linked developmental disorder. Patients with Tonne-Kalscheuer syndrome frequently have mutations in the RLIM gene. This then encodes an enzyme called RNF12, which plays critical functions in early development.

In addition to intellectual disability, male patients typically display urogenital abnormalities and hypogenitalism, where there is partial or complete failure of the genitalia to develop. Furthermore, female carriers of RNF12 mutations tend to present defects in fertility. This suggests that RNF12 performs a key role in reproductive development.

However, scientists remain uncertain about the pathways and systems that modify the expression and function of RNF12 on the molecular level.

RNF12 supports the formation of reproductive cells

The researchers used CRISPR gene editing and protein analysis to investigate male mouse embryonic stem cells that lacked the mouse version of RNF12 and reconstituted with human RNF12.

The team observed that under normal conditions, RNF12 supported the development of reproductive cells in mouse testes by initiating the degradation of REX1, a protein that represses genes involved in gametogenesis.

Using global quantitative proteomics, the researchers identified another de-repressed target. They found an additional enzyme, USP26, which inhibits the degradation of RNF12. This led to a transcriptional feed-forward loop that maintained gametogenesis.

The study revealed that introducing variants of RLIM previously linked to Tonne-Kalscheuer syndrome and male fertility disorders, disrupted the functions of RNF12. Similarly, introducing variants of USP26 disrupted the activation of pro-gametogenesis genes.

The authors caution that further work is necessary to determine the specific roles of RNF12 and USP26 in gametogenesis in vivo.

“This work reveals synergy within the ubiquitylation cycle that controls a key developmental process in gametogenesis and that is disrupted in human genetic disorders.”

Written by Poppy Jayne Morgan, Front Line Genomics

Image Credit: Canva