Imprinted genes exhibit silencing of one of the parental alleles during embryonicdevelopment. In a previous study imprinted genes were found to have reduced introncontent relative to a non-imprinted control set (Hurstet al., 1996). However, dueto the small sample size, it was not possible to analyse the source of this effect.Here, we re-investigate this observation using larger datasets of imprinted and control(non-imprinted) genes that allow us to consider mouse and human, and maternallyand paternally silenced, imprinted genes separately. We find that, in the human andmouse, there is reduced intron content in the maternally silenced imprinted genesrelative to a non-imprinted control set. Among imprinted genes, a strong bias isalso observed in the distribution of intronless genes, which are found exclusivelyin the maternally silenced dataset. The paternally silenced dataset in the human isnot different to the control set; however, the mouse paternally silenced dataset hasmore introns than the control group. A direct comparison of mouse maternally andpaternally silenced imprinted gene datasets shows that they differ significantly withrespect to a variety of intron-related parameters. We discuss a variety of possibleexplanations for our observations.
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