During spermiogenesis, protein transport mechanism along microtubule-based structures, such as the manchette and the flagellum, play a crucial role for the achievement of sperm morphology and motility. A failure of the formation of these structures and the related defects of the transport mechanism can lead to asthenozoospermia and/ or teratozoospermia and therefore, cause male infertility.
Preliminary investigation showed a significantly reduced amount of CBE1 (ciliated bronchial epithelium 1) in sperm of infertile men. CBE1, which was found previously in ciliated bronchial cells and in association with the microtubules of the spermatid manchette, is a largely uncharacterized protein. We hypothesize that CBE1 has a role in protein transport mechanisms during spermiogenesis and therefore to sperm motility.
We analyzed the expression pattern of CBE1 and the localization of the protein in human testicular biopsies with normal (n=10) and impaired spermatogenesis including arrest at level of spermatocytes (n=8) and round spermatids (n=8). We generated a mouse model using CRISPR-Cas9 technology to analyse the phenotypical consequences of CBE1 loss on mouse male infertility. Using BioID and CRISPR-Cas 9 technology, we are investigating the molecular function and interaction partners of CBE1 during ciliogenesis in IMCD3 cells.
CBE1 mRNA is expressed in pachytene primary spermatocytes, whereas the protein is clearly localized in association with microtubules of the manchette, the HTCA (head tail coupling apparatus) and the flagellum during spermiogenesis. The lower amount of CBE1 in human spermatozoa indicates an influence of CBE1 on spermatid development but not on the maintenance of mature sperms.
Testicular biopsies with an arrest at level of spermatids showed a reduced mRNA expression and immuno-negative elongating spermatids supporting a function of CBE1 in the development of sperm motility.
The current biochemical investigations of CBE1 will clarify the molecular role during ciliogenesis and the associated transport mechanism along microtubules.