Summary
In mammals, the increase in gene dosage, in the form of
polyploidy or involving chromosomal fragments, has deleterious
effects [1]. Regulation of appropriate gene product
amounts has to be warranted by complex dosage-compensation
mechanisms. Lower vertebrates, on the other hand,
cope very well with ploidy increase [2–4], implying either effective
compensation or a lack of necessity for such mechanisms.
Unfortunately, nothing is known about the genetic
and molecular mechanisms underlying this phenomenon.
For an experimental approach, we have studied gene expression
in the allotriploid form of Squalius alburnoides. In these
organisms, different genomes are joined through hybridization;
thus, sequence differences can be used to follow
expression of different alleles [5, 6].We found that a compensation
mechanism exists, reducing transcript levels to the
diploid state. Our data suggest a silencing of one of the three
alleles. Unexpectedly, it is not a whole haplome that is inactivated.
The allelic expression patterns differ between genes
and between different tissues for one and the same gene.
Our data provide the first evidence of a regulation mechanism
involving gene-copy silencing in a triploid vertebrate.