Mouse PeP: A novel peroxisomal protein linked to myoblast differentiation and development

The identification of several peroxisomal proteins in the past decade has deepened our understanding of the biology of peroxisomes and their involvement in human disorders. We report the cloning and expression pattern during the mouse development of a cDNA encoding a novel protein, named PeP, and show that its product is imported specifically to the peroxisome matrix in a variety of cell types. We also demonstrate that PeP is imported to the organelle through the PEX5 receptor pathway, which indicates that the C-terminal tripeptide SKI behaves as a type 1 peroxisomal targeting signal (PTS1). PeP expression is tightly regulated, as shown by Northern and in situ hybridization experiments. Thus during embryonic development in the mouse, PeP mRNA is detected almost exclusively in the skeletal muscle, whereas in adult mice, strong expression is also found in the heart and brain. In addition, PeP mRNA accumulation is induced after myoblast differentiation in vitro, when myotube formation is promoted. Sequence analysis reveals that PeP has no significant homology to any known protein, except for a short stretch of amino acids containing the fingerprint of the fibronectin type III superfamily, a domain present in proteins often related to molecular and cellular recognition and binding processes. Thus our data suggest a connection between the function of PeP and murine cell differentiation and development.