EXD2, also known as EXDL2, is an exonuclease with diverse essential functions. It plays roles in multiple biological pathways such as DNA double-strand break (DSB) repair, replication fork protection, telomere maintenance, and mitochondrial translation. Its functions are crucial for maintaining genomic integrity, cell viability, and normal cellular metabolism [1,2,3,4,5]. Genetic models, especially knockout models, are valuable for studying EXD2's functions.

In loss-of-function experiments, EXD2 deficiency leads to various phenotypes. In DSB repair, EXD2 is essential for DSB resection and efficient homologous recombination (HR) as it functionally interacts with the MRN complex to accelerate resection [4]. Regarding replication forks, EXD2 protects stressed replication forks; its deficiency causes fork collapse, hypersensitivity to replication inhibitors, and genomic instability [3]. In telomere maintenance, EXD2 nuclease is recruited to ALT telomeres, and its loss leads to telomere shortening, elevated telomeric sister chromatid exchanges, etc. [2]. In mitochondrial translation, loss of EXD2 results in defective mitochondrial translation, impaired respiration, and metabolic abnormalities [5].

In conclusion, model-based research has revealed that EXD2 is essential for DNA repair, replication fork protection, telomere maintenance, and mitochondrial translation. In disease-related aspects, its loss-of-function phenotypes suggest potential implications in cancers relying on alternative telomere lengthening and in cancers with BRCA1/2 mutations, highlighting its potential as a druggable target [2,3].

References:

1. Nieminuszczy, Jadwiga, Broderick, Ronan, Niedzwiedz, Wojciech. 2016. EXD2 - a new player joins the DSB resection team. In Cell cycle (Georgetown, Tex.), 15, 1519-20. doi:10.1080/15384101.2016.1161997. https://pubmed.ncbi.nlm.nih.gov/27247051/

2. Broderick, Ronan, Cherdyntseva, Veronica, Nieminuszczy, Jadwiga, Gagos, Sarantis, Niedzwiedz, Wojciech. 2023. Pathway choice in the alternative telomere lengthening in neoplasia is dictated by replication fork processing mediated by EXD2's nuclease activity. In Nature communications, 14, 2428. doi:10.1038/s41467-023-38029-z. https://pubmed.ncbi.nlm.nih.gov/37105990/

3. Nieminuszczy, Jadwiga, Broderick, Ronan, Bellani, Marina A, Seidman, Michael M, Niedzwiedz, Wojciech. 2019. EXD2 Protects Stressed Replication Forks and Is Required for Cell Viability in the Absence of BRCA1/2. In Molecular cell, 75, 605-619.e6. doi:10.1016/j.molcel.2019.05.026. https://pubmed.ncbi.nlm.nih.gov/31255466/

4. Broderick, Ronan, Nieminuszczy, Jadwiga, Baddock, Hannah T, McHugh, Peter J, Niedzwiedz, Wojciech. 2016. EXD2 promotes homologous recombination by facilitating DNA end resection. In Nature cell biology, 18, 271-280. doi:10.1038/ncb3303. https://pubmed.ncbi.nlm.nih.gov/26807646/

5. Silva, Joana, Aivio, Suvi, Knobel, Philip A, Yanes, Oscar, Stracker, Travis H. 2018. EXD2 governs germ stem cell homeostasis and lifespan by promoting mitoribosome integrity and translation. In Nature cell biology, 20, 162-174. doi:10.1038/s41556-017-0016-9. https://pubmed.ncbi.nlm.nih.gov/29335528/