Project description:Regulation of mRNA stability is a critical step in the control of gene expression. The nonsense mediated mRNA decay (NMD) pathway is one important mRNA stability pathway and has been shown to function in regulating a significant portion of the transcriptome. Perhaps the most significant outstanding question surrounding NMD regulation of endogenous gene expression is the identification of transcripts directly targeted by the NMD pathway versus secondary response genes, whose expression levels are dependent on the activity of direct targets. Here, we present for the first time in an intact animal, the experimental identification of direct targets of NMD. We find that most genes (74%) that are upregulated in NMD mutants appear not to be direct targets of NMD. More surprisingly, we find that the vast majority (97%) of candidate direct targets are not found to be increased in expression in a NMD mutant background. These results imply negative feedback renormalizes the levels of most direct targets of NMD, suggesting they would have been missed in previous analyses. We find that our candidate direct target genes have disproportionately long 3’ UTRs compared to non-targeted control genes. Long 3’ UTRs have been shown to target mRNAs for NMD in experimental systems, and our results imply this is the case in vivo. Our results will allow for the understanding of the function of the NMD pathway in endogenous gene regulation, during normal development, as well as in pathological states. Starting with a Nonsense Mediated Decay(NMD) mutant, in which expression levels of both primary and secondary NMD targets should be increased, we introduce a wild-type copy of the mutated factor and evaluated the transcriptome profile change overtime. Following reintroduction, expression levels of transcripts that are direct targets of NMD should decrease rapidly. Conversely, the levels of indirect targets will remain high until direct targets return to wild-type levels, which will occur later in the timecourse. This allows us to identify direct NMD targets.
Project description:Regulation of mRNA stability is a critical step in the control of gene expression. The nonsense mediated mRNA decay (NMD) pathway is one important mRNA stability pathway and has been shown to function in regulating a significant portion of the transcriptome. Perhaps the most significant outstanding question surrounding NMD regulation of endogenous gene expression is the identification of transcripts directly targeted by the NMD pathway versus secondary response genes, whose expression levels are dependent on the activity of direct targets. Here, we present for the first time in an intact animal, the experimental identification of direct targets of NMD. We find that most genes (74%) that are upregulated in NMD mutants appear not to be direct targets of NMD. More surprisingly, we find that the vast majority (97%) of candidate direct targets are not found to be increased in expression in a NMD mutant background. These results imply negative feedback renormalizes the levels of most direct targets of NMD, suggesting they would have been missed in previous analyses. We find that our candidate direct target genes have disproportionately long 3’ UTRs compared to non-targeted control genes. Long 3’ UTRs have been shown to target mRNAs for NMD in experimental systems, and our results imply this is the case in vivo. Our results will allow for the understanding of the function of the NMD pathway in endogenous gene regulation, during normal development, as well as in pathological states.
Project description:Identification of novel, highly penetrant, breast cancer susceptibility genes will require the application of additional strategies beyond that of traditional linkage and candidate gene approaches. Approximately one-third of inherited genetic diseases, including breast cancer susceptibility, are caused by frameshift or nonsense mutations that truncate the protein product [1]. Transcripts harbouring premature termination codons are selectively and rapidly degraded by the nonsense-mediated mRNA decay (NMD) pathway. Blocking the NMD pathway in any given cell will stabilise these mutant transcripts, which can then be detected using gene expression microarrays. This technique, known as gene identification by nonsense-mediated mRNA decay inhibition (GINI), has proved successful in identifying sporadic nonsense mutations involved in many different cancer types. However, the approach has not yet been applied to identify germline mutations involved in breast cancer. We therefore attempted to use GINI on lymphoblastoid cell lines (LCLs) from multiple-case, non-BRCA1/2 breast cancer families in order to identify additional high-risk breast cancer susceptibility genes. We applied GINI to a total of 24 LCLs,established from breast-cancer affected and unaffected women from three multiple-case non-BRCA1/2 breast cancer families. We then used Illumina gene expression microarrays to identify transcripts stabilised by the NMD inhibition. Total RNA obtained from the lymphoblastoid cell lines derived from 24 individuals.
Project description:The Upf1 protein is a major factor in nonsense-mediated decay. We used an in vivo labelling system (Cleary et al. 2005 Nat Biotechnol. 23, 232-7) to estimate the decay rates of upf1delta and wild type cells over-expressing the transcription factor Mei4.
Project description:Identification of novel, highly penetrant, breast cancer susceptibility genes will require the application of additional strategies beyond that of traditional linkage and candidate gene approaches. Approximately one-third of inherited genetic diseases, including breast cancer susceptibility, are caused by frameshift or nonsense mutations that truncate the protein product [1]. Transcripts harbouring premature termination codons are selectively and rapidly degraded by the nonsense-mediated mRNA decay (NMD) pathway. Blocking the NMD pathway in any given cell will stabilise these mutant transcripts, which can then be detected using gene expression microarrays. This technique, known as gene identification by nonsense-mediated mRNA decay inhibition (GINI), has proved successful in identifying sporadic nonsense mutations involved in many different cancer types. However, the approach has not yet been applied to identify germline mutations involved in breast cancer. We therefore attempted to use GINI on lymphoblastoid cell lines (LCLs) from multiple-case, non-BRCA1/2 breast cancer families in order to identify additional high-risk breast cancer susceptibility genes. We applied GINI to a total of 24 LCLs,established from breast-cancer affected and unaffected women from three multiple-case non-BRCA1/2 breast cancer families. We then used Illumina gene expression microarrays to identify transcripts stabilised by the NMD inhibition.
Project description:Nonsense-mediated mRNA decay (NMD) functions to degrade transcripts bearing premature stop codon (PTC) and is a crucial regulator of gene expression. NMD and the UPF3B gene have been implicated as the cause of various forms of intellectual disability (ID) and other neurological symptoms. Here, we reports three patients with global developmental delay carrying hemizygous deletions of the UPF2 gene, another important member of the NMD pathway and direct interacting partner of UPF3B.
Project description:We have HA-tagged two nonsense-mediated decay proteins, UPF1 and UPF2, in the malaria parasite Plasmodium falciparum. We then performed co-immunoprecipitation experiments to determine the protein-protein interactions of these nonsense-mediated decay components.