<i>Ccdc33, </i>a Predominantly Testis-Expressed Gene, Encodes a Putative Peroxisomal Protein

Abstract

Many genes crucial for male fertility are often predominantly or exclusively expressed in male germ cells. The analysis of mouse models has demonstrated the functional importance of peroxisomes in spermatogenesis. The CCDC33 protein has been reported to be a cancer/testis (CT) antigen. We found that mouse Ccdc33 is predominantly expressed in the testis and undergoes alternative splicing to produce at least 4 different transcripts. The protein encoded by Ccdc33 contains 3 coiled-coil domains, a C2-domain, 2 ER membrane retention signal-like motifs and 2 putative peroxisomal targeting signals type 2 (PTS2). We could demonstrate that the second PTS2 sequence is functional and responsible for the targeting of CCDC33 to peroxisomes. Moreover, in HeLa cells CCDC33-dsRED fusion protein co-localized with a known peroxisomal protein, namely PXT1, and showed punctuate intracellular distribution. Taken together, the mouse Ccdc33 encodes a putative peroxisomal protein and is predominantly expressed in male germ cells. The expression starts at the primary spermatocyte stage, suggesting an important role of this protein during spermatogenesis.

The peroxisome: an update on mysteries

“…As reported for brain in this review, recent studies in lung and testis also showed that the peroxisomal proteome in these tissues diverges significantly from the well-characterized liver and kidney peroxisomes (Karnati and Baumgart-Vogt 2009; Dastig et al 2011). In this respect, the continuous identification of novel tissue-specific peroxisomal proteins (Grzmil et al 2007;Kaczmarek et al 2009) will result in fascinating functional discoveries. Although our knowledge on peroxisome biogenesis has become increasingly detailed through recent years, many mysteries regarding the functional characterization and physiological role of peroxisomes lay ahead awaiting to be deciphered.…”

Human Sperm Tail Proteome Suggests New Endogenous Metabolic Pathways

“…That progressive loss of male fertility might be a conserved feature of peroxisomal biogenesis disorders is suggested by observations in Drosophila models (75), as well as in knock-out mice for peroxisomal multifunctional protein 2 (76). The relevance of peroxisomes in spermatogenesis is additionally illustrated by the existence of the male-germ-cell-specific peroxisomal proteins PXT1 (77) and CCDC33 (78), the expression of which starts at the spermatocyte stage. In view of that, it was proposed that instead of being degraded, peroxisomes might remodel their proteome during spermatogenesis to acquire new functions (68).…”

Overexpression of peroxisomal testis-specific 1 protein induces germ cell apoptosis and leads to infertility in male mice

“…Transfection was performed, as described (Grzmil et al, 2007; Kaczmarek et al, 2009), with 1 μg (for single transfection) or 2 × 0.5 μg (for cotransfection) of construct(s) DNA. After 24 h of transient transfection, the cells were fixed with 4% paraformaldehyde and 0.1% Tween 20 for 15 min at RT.…”