A minor alternative transcript of the fumarylacetoacetate hydrolase gene produces a protein despite being likely subjected to nonsense-mediated mRNA decay.
BACKGROUND
Coupling of alternative splicing with nonsense-mediated mRNA decay (NMD) may regulate gene expression. We report here the identification of a nonsense alternative transcript of the fumarylacetoacetate hydrolase (fah) gene, which produces a protein despite the fact that it is subject to NMD.


RESULTS
During the characterization of the effects of the W262X nonsense mutation on FAH mRNA metabolism, two alternative transcripts (del100 and del231) of the fah gene were identified. Del100 lacks exon 8 and as a consequence, the reading frame is shifted and a premature termination codon appears at the 3'end of exon 10. Exons 8 and 9 are skipped in del231, without any disruption of the reading frame. Specific amplification of these transcripts demonstrate that they are produced through minor alternative splicing pathways, and that they are not caused by the W262X mutation per se. As shown with an antiserum raised against the C-terminal part of the putative DEL100 protein, the del100 transcript produces a protein, expressed at different levels in various human tissues. Interestingly, the del100 transcript seems to be subjected to nonsense-mediated mRNA decay, as its level was stabilized following a cycloheximide treatment.


CONCLUSIONS
The del100 and del231 transcripts arise due to minor alternative splicing pathways and del100 is likely subjected to nonsense-mediated mRNA decay. However the remaining amount of transcript seems sufficient to produce a protein in different human tissues. This suggests that NMD has a broader role than simply eliminating aberrant transcripts and when coupled to alternative splicing, may act to modulate gene expression, by allowing the production of low amounts of protein.
Dreumont
Natacha
N
Laboratory of Cellular and Developmental Genetics, CREFSIP, Dept Medicine, Université Laval, Pavillon Marchand, Ste-Foy, Québec, Canada G1K 7P4. natacha.dreumont.1@ulaval.ca <natacha.dreumont.1@ulaval.ca>
Maresca
Antonella
A
Boisclair-Lachance
Jean-François
JF
Bergeron
Anne
A
Tanguay
Robert M
RM
D017398:Alternative Splicing / Q000235:genetics; D018389:Codon, Nonsense; D005786:Gene Expression Regulation; D006801:Humans; D006867:Hydrolases / Q000235:genetics*; D009154:Mutation; D014176:Protein Biosynthesis; D012322:RNA Precursors / Q000378:metabolism*; D020871:RNA Stability / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D018389:Codon, Nonsense; D012322:RNA Precursors; D012333:RNA, Messenger; D006867:Hydrolases; C020156:fumarylacetoacetase