Fig. 4

Possible evolutionary fates for the USP paralogs in Platyhelminthes parasites. First, a new USP copy can accumulate deleterious mutations, leading to alterations in the protein sequence with a loss of function (pseudogenization). From this, some ncRNAs can be transcribed, and thus, regulate the gene expression of the other USP paralogs via mRNA degradation (regulation by ncRNAs). Second, the USP paralog could undergo several non-synonymous mutations, thereby acquiring a new function (neofunctionalization). Finally, some USP copies could maintain the same function, but be expressed in a specific life cycle stage or in response to a specific stressor (subfunctionalization).