Description of the thesis topic

Although extensive research has been conducted on the impact of genotoxic agents on DNA and the subsequent repair processes, our understanding of the molecular mechanisms underlying the restoration of cellular functions after DNA repair remains limited. While there are error-free and error-prone bypass mechanisms for DNA lesions that help avoid damage during DNA replication, DNA lesions that block transcription present a significant challenge. Overcoming the transcription-blocking effects of DNA damage is crucial for cell viability. Moreover, DNA lesions not only obstruct transcription but may also disrupt the correct positioning of chromatin domains within the nucleus and alter nucleolar organization.
The nucleolus is a membrane-less organelle whose internal organization reflects its different functions in ribosome biogenesis: the transcription of ribosomal DNA (rDNA) and early ribosomal RNA (rRNA) maturation. This highly organized structure can be profoundly altered by both genotoxic agents and general cellular stress. In recent years, the host laboratory has shown that after genotoxic stress (UV: ultraviolet irradiation), RNA polymerase I (RNAP1) and nucleolar DNA are exported to the periphery of the nucleolus. Interestingly, after the complete repair of DNA lesions, proper nucleolar organization is fully restored.
However, the precise mechanism underlying the restoration of nucleolar structure after DNA damage induction remains largely unexplored.

Very recently, the host laboratory discovered that the SMN protein (Survival of Motor Neuron), which is altered in patients suffering from spinal muscular atrophy (SMA), plays a fundamental role in restoring nucleolar organization following UV exposure. In addition to SMN, other proteins such as Fibrillarin (FBL), Coilin, Nuclear Myosin 1 (NM1), and Actin-beta (Act-b) also appear to be important in this process.

Based on our latest findings, we propose a research hypothesis suggesting that nucleolar homeostasis, following the completion of DNA repair, is not merely a passive phenomenon. It is plausible that numerous proteins play a key role in restoring the correct nucleolar organization.

The general aim of this thesis project is to elucidate the mechanisms governing nucleolar reorganization after the induction of DNA lesions, ensuring the maintenance of proper nucleolar homeostasis upon the completion of DNA repair.

The thesis project aims to achieve the following objectives:

1. Identify the critical factors governing nucleolar homeostasis during and after DNA repair.
2. Investigate the dynamic reorganization of nucleoli following genotoxic stress and elucidate the mechanism by which nucleolar homeostasis is restored once DNA repair is completed.

Work Context

Our Neuron and Muscle Pathophysiology and Genetics Unit is located on the Rockefeller campus in Lyon and is made up of 10 teams and around 120 people. The research themes are the study of the physiology and cell biology of muscle cells and neurons, in particular of the molecular mechanisms which involve cell differentiation. The host team works on transcription by RNA polymerase 1 and 2 and DNA repair by nucleotide excision. The Doctoral Student (M/F) will be under the responsibility of Dr Mari Pierre-Olivier.

Constraints and risks

Possibility to work outside of regular hours.