Alterations in gene processing impact gene expression

The PRC2 component SUZ12 is present in two alternative splicing isoforms depending on the inclusion or exclusion of SUZ12 fourth exon - represented by squares on both sides. On the one hand, the ancestral isoform mainly acts in a monomeric complex – symbolized by the red semicircle – that methylates nucleosomes on vast portions of the genome. On the other hand, the novel isoform is able to focus PRC2 activity on gene promoters, by favoring PRC2 dimerization. The exon involved in this splicing event is constitutively included in non-eutherian mammals, including marsupials (represented by a kangaroo) and only becomes alternative in placental mammals (represented by a deer), where the two isoforms are coexpressed and contribute to modify chromatin.