Although there is no doubt that high doses of ionising radiation such as X-rays and gamma rays can have serious biological consequences, the risks of low doses on human health are still unclear.

Understanding the effects associated with low doses of radiation is of great importance from a social point of view, precisely because of the constant exposures we are subjected to on a daily basis, during work or medical screenings, but also from frequent air travel. Determining these risks with certainty, primarily on model organisms, is, therefore, one of the central tasks of radiation epidemiology and biology.

A new study, coordinated by Giovanni Cenci of the Charles Darwin Department of Biology and Biotechnology of Sapienza University of Rome, has shown that chronic exposure of the common fruit fly (Drosophila melanogaster) to low doses of radiation during development makes the cells of this model organism resistant to the occurrence of chromosomal breaks (a consequence of DNA damage) induced later by high doses of gamma rays. In addition, RNA sequencing of the exposed fruit fly made it possible to understand for the first time that this type of response, termed 'Radio Adaptive Response (RAR)', is associated with reduced gene expression, called Loquacious.

The research, a collaboration between Sapienza University of Rome, the Istituto Superiore di Sanità and the University of Padua and supported by grants from the FERMI Institute for Multidisciplinary Studies, ISS-INFN and the Pasteur Institute, was published in the journal Communications Biology.

"The Adaptive Radio Response," says Antonella Porrazzo, first author of the article, "is a well-known phenomenon in the field of radiobiology. Thanks to Libis, a unique low-dose irradiator provided by collaborators of the Istituto Superiore di Sanità, we have shown that this response has its maximum effect only at a particular combination of dose and dose rate. Moreover, resistance to DNA damage induced by subsequent acute exposure is present in the offspring of fruit flies exposed to low doses, highlighting a clear and interesting transgenerational effect".

This study also showed that low-dose exposure reduces the frequency of telomere fusions (complex structures located at the chromosome end regions), which occur due to the malfunctioning of proteins that protect chromosome ends.

"Our observations," highlights Giovanni Cenci, research coordinator, "indicate that the protective effect of low doses can be extended to all those chromosomal sites that are inappropriately recognised as DNA breaks".

Genetic analyses have also shown that mutants in the Loquacious gene, which encodes a protein capable of binding double-stranded RNA and is also present in humans, are resistant to high-dose-induced chromosomal damage.

These results clearly indicate that modulation of the Loquacious gene represents an efficient cellular strategy for preserving chromosome integrity following genotoxic stress.

"Since the gene in question is also in our cells", Giovanni Cenci concludes, "future studies could clarify its possible involvement in the radioresistance phenomena observed in many tumours".

References:

Low dose rate γ-irradiation protects fruit fly chromosomes from double strand breaks and telomere fusions by reducing the esi-RNA biogenesis factor Loquacious – Antonella Porrazzo, Francesca Cipressa, Alex De Gregorio, Cristiano De Pittà, Gabriele Sales, Laura Ciapponi, Patrizia Morciano, Giuseppe Esposito, Maria Vittoria Tabocchini, Giovanni Cenci – Communications Biology (2022) https://doi.org/10.1038/s42003-022-03885-w

Further Information

Giovanni Cenci
Department of Biology and Biotechnology "Charles Darwin"
giovanni.cenci@uniroma1.it