All three MutL complexes are required for repeat expansion in a human stem cell model of CAG-repeat expansion mediated glutaminase deficiency

• Published in: Scientific reports Vol. 14; no. 1; pp. 13772 - 10
• Main Authors: Hayward, Bruce, Kumari, Daman, Santra, Saikat, van Karnebeek, Clara D. M., van Kuilenburg, André B. P., Usdin, Karen
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 14.06.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 5' Untranslated Regions; 631/208/211/2120; 631/337; 631/45/147; 631/45/173; Ataxia; Cell culture; Child development; Cooperation; CRISPR; CRISPR-Cas Systems; Disease; Endocrinology; GDPAG; GLSD; Glutaminase; Glutaminase - genetics; Glutaminase - metabolism; Glutaminase deficiency disorder; Humanities and Social Sciences; Humans; Induced Pluripotent Stem Cells - metabolism; Metabolic disorders; Microsatellite instability; Mismatch repair; Mismatch repair (MMR); multidisciplinary; MutL Proteins - genetics; MutL Proteins - metabolism; Plasmids; Pluripotency; Polyglutamine; R-loops; Repeat expansion disease; Science; Science (multidisciplinary); Stem cells; Trinucleotide Repeat Expansion - genetics; Trinucleotide repeats; Yeast; Mismatch repair (MMR); Repeat expansion disease; GDPAG; Microsatellite instability; Glutaminase deficiency disorder; GLSD
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-024-64480-z

The Repeat Expansion Diseases (REDs) arise from the expansion of a disease-specific short tandem repeat (STR). Different REDs differ with respect to the repeat involved, the cells that are most expansion prone and the extent of expansion. Furthermore, whether these diseases share a common expansion mechanism is unclear. To date, expansion has only been studied in a limited number of REDs. Here we report the first studies of the expansion mechanism in induced pluripotent stem cells derived from a patient with a form of the glutaminase deficiency disorder known as Global Developmental Delay, Progressive Ataxia, And Elevated Glutamine (GDPAG; OMIM# 618412) caused by the expansion of a CAG-STR in the 5′ UTR of the glutaminase ( GLS ) gene. We show that alleles with as few as ~ 120 repeats show detectable expansions in culture despite relatively low levels of R-loops formed at this locus. Additionally, using a CRISPR-Cas9 knockout approach we show that PMS2 and MLH3, the constituents of MutLα and MutLγ, the 2 mammalian MutL complexes known to be involved in mismatch repair (MMR), are essential for expansion. Furthermore, PMS1, a component of a less well understood MutL complex, MutLβ, is also important, if not essential, for repeat expansion in these cells. Our results provide insights into the factors important for expansion and lend weight to the idea that, despite some differences, the same mechanism is responsible for expansion in many, if not all, REDs.