Functional characterization of a PHF8 processed pseudogene in the mouse genome

The majority of pseudogenes are generated when an RNA transcript is reverse-transcribed and integrated into the genome at a new location. Pseudogenes are often considered as an imperfect and silent copy of a functional gene because of the accumulation of numerous mutations in their sequence. Here we report the presence of PHF8-ps , a PHF8 retrotransposed pseudogene in the mouse genome, which has no disruptions in its coding sequence. We showed that this pseudogene was specifically transcribed in testis and can produce a Phf8-ps protein in vivo. As Phf8-ps protein has a well-conserved JmjC domain, we characterized its enzymatic activity and showed that Phf8-ps did not have the intrinsic capability to demethylate H3K9me2 in vitro compared to the parental Phf8 protein. Surprisingly, Phf8-ps did not localize in the nucleus like Phf8 but rather was mostly located at the cytoplasm. Finally, our proteomic analysis of Phf8-ps associated proteins revealed that Phf8-ps interacted with mitochondrial proteins but also with prefoldin subunits (PFDN proteins) that deliver unfolded proteins to the cytosolic chaperonin complex implicated the folding of cytosolic proteins. Together, our findings highlighted Phf8-ps as a new pseudogene-derived protein with distinct molecular functions from Phf8.