Régulation de voies de signalisation par deux acteurs de la voie Nonsense-mediated Decay, Dhx34 et Nbas: la cas particulier de l'adénohypophyse.
In eukaryotes, biosynthesis of functional mRNAs is the core process of genetic expression and is monitored by highly conserved pathways that prevent appearance of aberrant mRNAs. Amongst them the Nonsense-Mediated Decay (NMD) pathway is the surveillance mechanism that detects and degrades mRNAs containing premature termination codons (PTCs). The translation of transcripts containing such nonsense codon within the coding sequence would leads to the production of C-terminally truncated proteins that could exhibit dominant negative or gain-of-function activities. The NMD is thus a key determinant of the phenotypic outcome of numerous diseases involving PTCs such as the β-thalassemia, the Duchenne muscular dystrophy or even some cancers. In addition to its quality control function degrading aberrant mRNA, the NMD is also involved in the abundance regulation of several physiological transcripts. For example the NMD is involved in the regulation of the concentration of splicing factors in a process called AS-NMD (Alternative splicing- Nonsense-mediated Decay), establish a threshold for some stress responses such as the UPR pathway (Unfolded Protein Response) and constitute a defence mechanism against ARN(+) viruses. Despite tremendous studies, the study of the developmental and physiological impact of the NMD pathway is restrained due to the early lethality of the mammals embryos that underwent knock-out of one of the NMD actor. As an alternative model we propose Danio rerio which as a vertebrate with external development and a large panel of genetic inactivation methods is a wonderful model for developmental studies and represent a excellent tool to study the NMD pathway. Initial studies in zebrafish conducted by morpholino knock-down, showed that depletion of upf1, upf2, smg5, smg6, dhx34 or nbas leads to the NMD blockage and induce similar developmental defects mainly in brain, eyes and somites. Moreover, it’s has been showed that as in mammals the NMD in fish also implicated in the regulation of natural transcripts. We present here a functional study of two key actors of the NMD, Dhx34 and Nbas, in the interesting case of the pituitary gland development. In the present study, we shed light on the NMD pathway importance for the developmental process of the pituitary gland. Using in situ hybridization confirmed by RT-qPCR quantification, we observed that the NMD inactivation thought inhibition of two crucial actors of this surveillance pathway, Dhx34 and Nbas, lead to a hypertrophy of the gland coupled with a promotion of the anterior cell fates and a repression of the posterior fates at 2 dpf. We proved that this endocrine deregulation is due to a late general increase of the Sonic Hedgehog and Delta-Notch signalling during AH formation. In addition to previous works, our results show that the NMD pathway is required to control the activity diverse signalling pathways involved in the developmental process. As confirmation, we could observe serious abnormalities in a variety of tissues such as underdeveloped eyes, intestine, liver and skeleton, defects in brain, somites and vascular patterning.
Nonsense-mediated Decay, Adenohypophysis, Danio rerio, Life sciences, Biochemistry, biophysics & molecular biology, Sciences du vivant, Biochimie, biophysique & biologie moléculaire
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