Generation of processed pseudogenes in murine cells.

Using as a reporter gene a non‐coding proviral structure marked with an intron‐containing indicator, we demonstrate the de novo formation, via a retrotransposition pathway, of canonical processed pseudogenes in cultured mammalian cells. Their structural features include endings corresponding to the start and termination of the RNA intermediate, intron loss, acquisition of a 3′ poly(A) tail, and target site duplications of variable length. The absence of extracellular intermediates for these processes, and the elimination during retrotransposition of sequences in the reporter gene essential in cis for a retroviral cycle, further suggest that endogenous retroviruses or related elements are not involved. Pseudogene formation frequency is markedly increased (up to 10‐fold) by several treatments including treatment with 5‐azacytidine or tetradecanoyl phorbol acetate, or serum starvation, which do not act at the reporter gene transcription level, but rather on endogenous genes‐‐including the LINE elements‐‐necessarily involved in trans‐complementation for retrotransposition.