Nicola Silva's research seeks to answer one of the fundamental, unanswered biological questions

Some of the most deleterious stimuli that can compromise genome integrity and lead to cancer development include physical interruptions to both DNA strands, called double-strand breaks (DSBs). It is not only the different stages of DSB that Dr. Nicola Silva from the Department of Biology, Faculty of Medicine, MU, is focusing on in his research.

30 Sep 2022

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In mitotic somatic cells, DSBs are unscheduled and occur due to DNA replication and/or transcription mistakes. Given their dangerous potential, the presence of lesions along the DNA is promptly detected by cellular machineries, which in turn promote their accurate repair. If left unresolved or not repaired properly, DSBs can elicit massive apoptotic cell death or lead to cellular transformation respectively.

On the other hand, during oocyte and sperm meiosis, the induction of DSBs is purposedly induced to promote the correct segregation of the homologous chromosomes (the paternal and maternal copy of each chromosome in the diploid cells) into the gametes by allowing homologous recombination to take place.

Nicola Silva:

"Our analysis was entirely performed in a metazoan model (Caenorhabditis elegans) in vivo with a high degree of precision in our temporal assessments of the meiotic phenotypes. The data provide a visual mean to actually observe what happens to gametes that receive the wrong number of chromosomes as recombination fails to take place."

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The team of Dr. Silva´s lab in collaboration with Sarit Smolikove´s research group at the Iowa University were interested in studying the temporal regulation of meiotic DNA double-strand break (DSB) induction, a fundamental biological question that has remained unanswered so far. Since the experimental tools became recently available, in particular the spo-11::AID functional tagged line generated by CrispR in the Dernburg´s lab (Zhang et al.; 2018, eLife), they sought to investigate how the formation of the SPO-11-dependent breaks and their DNA-2-EXO-1-mediated processing (end resection) were coordinated in vivo in a metazoan model.

The data show that, (a) contrary to what was believed (whereby meiotic breaks are induced only at meiotic entry and then differentially repaired to form both recombinant and non-recombinant outcomes), meiotic DSBs are induced continuously from early meiotic entry to late pachytene stage (one of the substages of meiotic Prophase I). Moreover, (b) the team found that strikingly only the DSBs formed at later stages are instrumental for crossover formation and that (c) DNA-2-EXO-1-depenent end resection specifically acts on later DSBs to promote accurate repair.

The study unraveled previously unknown details about an essential aspect of meiotic chromosome segregation. Induction of meiotic DSBs is essential for accurate partitioning of the genetic information during gametogenesis and failure in their formation or repair, leads to the generation of gametes with the wrong chromosome number or chromosome aberrations that can give raise to miscarriages, sterility, or inheritable mutations to the offspring. Therefore, a thorough understanding of how this biological mechanism works is crucial to human health. This is the first study in which the temporal activity of SPO-11 as well as of DNA-2/EXO-1 could be analysed in vivo, and as such it represents a crucial finding for the field.

The collaborative work has been published on September 27th in the prestigious journal Cell Reports. The data were previously presented by our collaborator Assoc. Prof. Sarit Smolikove at the 2022 Meiosis Gordon Research Conference held at the Colby-Sawyer College in New London (USA) last June.

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