Control of mRNA 3’-end formation during Drosophila neural development: mechanisms and biological roles

The process of alternative polyadenylation (APA) is a widespread gene regulatory mechanism that generates mRNAs with different 3’ ends, allowing mRNAs to interact with different sets of RNA regulators such as microRNAs and RNA-binding proteins. Recent studies have shown that during development in both insects and mammals, mRNAs with extended 3’ UTRs are restricted to the nervous system suggesting that extended 3’ UTRs might play important roles during the formation and function of the nervous system. With its powerful genetics Drosophila emerges as an excellent system to study the molecular mechanisms and biological roles of APA within the physiological context of neural development. Much of the work is centred in the roles of the Cleavage Factor I (CFI) complex, because (i) is the complex with the highest evolutionary conservation between humans and Drosophila, (ii) it is expressed at very high level in neural tissues, and (iii) has a well-established structure and function in mammalian cells. Through the combination of genetic, molecular and genomic databases, I first show that the cleavage and polyadenylation (CPA) machinery in Drosophila is as complex as its human counterpart and shows an enrichment of expression in the nervous system. Secondly, using a suite of genetic and behavioural methods, I show that a mutation in the Drosophila orthologue of CFI25 affects feeding in the Drosophila larvae and is required for major developmental transitions. Third, I explore the mechanisms by which APA is controlled in the developing nervous system by CFI factor depletion. As a result of this, genes with reported neural 3’ UTR extensions change their patterns of APA. Altogether, this work adds to the current understanding of the phenomenon of APA within the nervous system and gives new insights on the biological roles of CPA factors for behaviour and neural function

Identification and characterization of novel factors that act in the nonsense-mediated mRNA decay pathway in nematodes, flies and mammals

Nonsense-mediated mRNA decay (NMD) is a surveillance mechanism that degrades mRNAs harboring premature termination codons (PTCs). We have conducted a genome-wide RNAi screen in Caenorhabditis elegans that resulted in the identification of five novel NMD genes that are conserved throughout evolution. Two of their human homologs, GNL2 (ngp-1) and SEC13 (npp-20), are also required for NMD in human cells. We also show that the C. elegans gene noah-2, which is present in Drosophila melanogaster but absent in humans, is an NMD factor in fruit flies. Altogether, these data identify novel NMD factors that are conserved throughout evolution, highlighting the complexity of the NMD pathway and suggesting that yet uncovered novel factors may act to regulate this process