Nonsense-associated alternative splicing of the human thyroglobulin gene.
BACKGROUND
We have described in previous articles a nonsense mutation (4588C>T, R1511X) in exon 22 of the thyroglobulin (TG) gene in a member of a family with a complex history of congenital goiter. In the mutated thyroid gland, full-length thyroglobulin mRNA is almost undetectable. However, a smaller transcript is detected in which the mutated exon 22 is skipped and the reading frame restored. It is conceivable that alternative splicing might be a mechanism involved in the rescue of nonsense mutations.


METHODS
To investigate whether the detection of the alternative mRNA is due to an increase in its concentration or its preferential amplification during reverse transcriptase-PCR in the absence of the normal full-length mRNA competitor, we set up an assay in which the competitor mRNA was provided. We also studied the effect of the 4588C>T mutation on exon definition and processing using wild-type and mutated minigenes.


RESULTS
The detection of the alternative mRNA lacking exon 22 is not caused by the absence of the full-length competitor. In contrast, our results demonstrate that the alternative transcript preferentially accumulates in the mutated thyroid at a level similar to the full-length transcript in control tissue. Transient expression experiments with wild-type and mutated minigenes indicate that the mutated exon is as efficiently spliced as the wild-type, suggesting that the 4588C>T mutation does not interfere with exon 22 definition and processing.


CONCLUSIONS
The alternative splicing of the TG gene described in this article constitutes a new case of nonsense-associated alternative splicing. We have shown that the mutation itself does not interfere with exon definition and processing in vitro. Our results support the hypothesis that the alternative splicing of the mutated exon is driven by the interruption of the reading frame.
Mendive
Fernando M
FM
Laboratory of Molecular Biology, Department of Genetic and Molecular Biology, School of Pharmacy and Biochemistry, University of Buenos Aires, Argentina.
Rivolta
Carina M
CM
González-Sarmiento
Rogelio
R
Medeiros-Neto
Geraldo
G
Targovnik
Héctor M
HM
D017398:Alternative Splicing / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D018389:Codon, Nonsense / Q000235:genetics*; D005091:Exons / Q000235:genetics; D015894:Genome, Human; D006801:Humans; D007438:Introns / Q000235:genetics; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013954:Thyroglobulin / Q000737:chemistry / Q000235:genetics*; D013961:Thyroid Gland / Q000378:metabolism
D018389:Codon, Nonsense; D012333:RNA, Messenger; D013954:Thyroglobulin