PARP1 and PARP2 are the most extensively studied proteins of the poly(ADP-ribose) polymerase (PARP) family. They share partially overlapping functions. These two proteins are best known for their roles in DNA repair. The DNA damage response is actually the most active area of research involving the PARP proteins given the success of PARP inhibitors for cancer therapy. However, PARPs possess many other functions. PARP3, a very little characterized protein, appears to be somewhat involved in the response to DNA damage by genotoxic agents but its physiological function is unknown. Recent evidence indicated that PARP3 is involved in the epigenetic regulation of transcription. For this reason, our collaborators identified PARP3-bound genes by screening the genomic occupancy of PARP3 and found that PARP3-bound genes associate with developmental transcription factors especially involved in neurogenesis. We used zebrafish, a well established vertebrate model in developmental biology, to study the role of PARP3 in development. By knocking-down Parp3 in zebrafish, we found that the loss of Parp3 function reduces the expression of neural crest “specifier” sox9a and of dlx3b/dlx4b. It impairs the formation of cranial sensory placodes, inner ears and pectoral fins. It delays pigmentation and severely impedes the development of the median fin fold and tail bud. In parallel, the reduced expression of Parp3 leads to a massive increase in apoptosis. I also knocked-down Parp1 and Parp2 in zebrafish. Results suggest that the function of Parp1 is different from that of Parp3 in zebrafish while the data from Parp2 were inconclusive. Our findings demonstrate that Parp3 is essential during early stages of zebrafish development, possibly by exerting its transcriptional regulatory functions during the specification of the neural plate border and by mediating cell survival during the early stages of development.

PARP1 and PARP2 are the most extensively studied proteins of the poly(ADP-ribose) polymerase (PARP) family. They share partially overlapping functions. These two proteins are best known for their roles in DNA repair. The DNA damage response is actually the most active area of research involving the PARP proteins given the success of PARP inhibitors for cancer therapy. However, PARPs possess many other functions. PARP3, a very little characterized protein, appears to be somewhat involved in the response to DNA damage by genotoxic agents but its physiological function is unknown. Recent evidence indicated that PARP3 is involved in the epigenetic regulation of transcription. For this reason, our collaborators identified PARP3-bound genes by screening the genomic occupancy of PARP3 and found that PARP3-bound genes associate with developmental transcription factors especially involved in neurogenesis. We used zebrafish, a well established vertebrate model in developmental biology, to study the role of PARP3 in development. By knocking-down Parp3 in zebrafish, we found that the loss of Parp3 function reduces the expression of neural crest “specifier” sox9a and of dlx3b/dlx4b. It impairs the formation of cranial sensory placodes, inner ears and pectoral fins. It delays pigmentation and severely impedes the development of the median fin fold and tail bud. In parallel, the reduced expression of Parp3 leads to a massive increase in apoptosis. I also knocked-down Parp1 and Parp2 in zebrafish. Results suggest that the function of Parp1 is different from that of Parp3 in zebrafish while the data from Parp2 were inconclusive. Our findings demonstrate that Parp3 is essential during early stages of zebrafish development, possibly by exerting its transcriptional regulatory functions during the specification of the neural plate border and by mediating cell survival during the early stages of development.

PARP1 and PARP2 are the most extensively studied proteins of the poly(ADP-ribose) polymerase (PARP) family. They share partially overlapping functions. These two proteins are best known for their roles in DNA repair. The DNA damage response is actually the most active area of research involving the PARP proteins given the success of PARP inhibitors for cancer therapy. However, PARPs possess many other functions. PARP3, a very little characterized protein, appears to be somewhat involved in the response to DNA damage by genotoxic agents but its physiological function is unknown. Recent evidence indicated that PARP3 is involved in the epigenetic regulation of transcription. For this reason, our collaborators identified PARP3-bound genes by screening the genomic occupancy of PARP3 and found that PARP3-bound genes associate with developmental transcription factors especially involved in neurogenesis. We used zebrafish, a well established vertebrate model in developmental biology, to study the role of PARP3 in development. By knocking-down Parp3 in zebrafish, we found that the loss of Parp3 function reduces the expression of neural crest “specifier” sox9a and of dlx3b/dlx4b. It impairs the formation of cranial sensory placodes, inner ears and pectoral fins. It delays pigmentation and severely impedes the development of the median fin fold and tail bud. In parallel, the reduced expression of Parp3 leads to a massive increase in apoptosis. I also knocked-down Parp1 and Parp2 in zebrafish. Results suggest that the function of Parp1 is different from that of Parp3 in zebrafish while the data from Parp2 were inconclusive. Our findings demonstrate that Parp3 is essential during early stages of zebrafish development, possibly by exerting its transcriptional regulatory functions during the specification of the neural plate border and by mediating cell survival during the early stages of development.

La poly(ADP-ribosyl)ation est une modification post-traductionnelle des protéines par les poly(ADP-ribose) polymérases (PARPs). PARP3 a été identifiée comme un nouvel acteur de la réparation des cassures double-brin (DSBs). Nous avons évalué la contribution de PARP3 dans les différentes voies de réparation (HR, C-NHEJ ou A-EJ). Les résultats obtenus définissent PARP3 comme un modulateur de l’étape de résection d’ADN simple-brin permettant d’engager le choix de la voie de réparation. Nous avons montré que PARP3 favorise le recrutement du complexe Ku70/Ku80 aux sites de cassures et module la balance BRCA1/53BP1. Ces deux événements limitent l’étape de réparation de la voie HR et A-EJ et oriente la réparation vers la voie du C-NHEJ. Par immunoprécipitation de la chromatine, nous avons étudié les conséquences de l’absence de PARP3 sur les modifications d’histones, connues pour moduler la décision entre les différentes voies de réparation. Nos résultats actuels ne nous ont pas permis d’établir de lien entre PARP3 et les modifications d’histones en réponse aux DSBs. Nous avons toutefois observé qu’en absence de dommages, l’absence de PARP3 induit un enrichissement de H3K36me2 une marque d’histone connue pour réguler les gènes transcriptionnellement actifs. Dans un second projet, nous avons étudié l’impact de l’absence de PARP3 sur la viabilité cellulaire et la progression tumorale de cellules cancéreuses mutées en BRCA1. Nous avons montré par des approches in vitro et in vivo que l’absence de PARP3 induit une diminution de la survie et de la prolifération cellulaire plus marquée, une amplification exacerbée des centrosomes, ainsi qu’un ralentissement plus important de la progression tumorale, faisant de PARP3 une cible prometteuse en thérapie du cancer. / Poly(ADP-ribosyl)ation is a post-translational modification of proteins catalyzed by poly(ADPribose) polymerases (PARPs). PARP3 was identified as a novel actor of the double-strand break (DSBs) repair pathway. We evaluated the contribution of PARP3 in these repair pathways(HR, C-NHEJ ou A-EJ). Our results defined PARP3 as a modulator of the single strand DNA resection process which plays a role in driving the repair pathway choice. We showed that PARP3 enhances the recruitement of the Ku70/Ku80 complexe to damaged sites and modulates the BRCA1/53BP1 balance. These two events prevent the DNA end resection step initiating HR and A-EJ and drives the repair towards the C-NHEJ. By chromatin immunoprecipitation, we studied the consequences of the absence of PARP3 on histone modifications, known to modulate the decision of the DSBs repair pathways. Our current results didn’t allow us to establish a link between PARP3 and histone modifications in response to DSBs. However, in absence of DNA damage and PARP3, we observed an accumulation of H3K36me2, a histone mark known to regulate transcriptionally active genes. In a second project, we studied the impact of the absence of PARP3 on cell viability and tumor progression in breast cancer cell lines mutated in BRCA1. By in vitro and in vivo approaches, we showed that the absence of PARP3 induces an important decrease in cell survival and proliferation, an increase in centrosomal amplification and a strong delay in tumor progression. The roles of PARP3 in both cellular response to DNA damage and mitotic progression introduce PARP3 as a possible promising therapeutic target in cancer therapy.