Molecular dissection of ODF2/Cenexin revealed a short stretch of amino acids necessary for targeting to the centrosome and the primary cilium.

The outer dense fiber protein ODF2 is the major component of the sperm tail cytoskeleton and a critical component of the mature centriole of the centrosome. Centriole maturation involves the formation of appendages and the recruitment of ODF2/Cenexin. ODF2 and Cenexin are alternative splice variants that differ in a short stretch of amino acids at their N-terminal regions encoded by exon 3b. Whereas Cenexin is ubiquitously expressed, Odf2 is the predominant transcript of testes [Hüber, D., Hoyer-Fender, S., 2007. Alternative splicing of exon 3b gives rise to ODF2 and Cenexin. Cytogenet. Genome Res. 119, doi:10.1159/000109621]. Here, we show that testicular expression of Odf2 correlates with spermiogenesis and ongoing sperm tail formation thus implicating functional differences between ODF2 and Cenexin. By generation of a series of ODF2/Cenexin deletion constructs fused to GFP and inspection of their subcellular localization in transfected NIH3T3 cells we found that a peptide of 42 amino acids specific for Cenexin is necessary for targeting ODF2/Cenexin to the centrosome and the primary cilium. Additionally, this region is also necessary for the formation of ODF2/Cenexin fibers that are associated with acetylated microtubules. Centrosomal targeting of ODF2/Cenexin does not depend on dynein-mediated transport further supporting an alternative targeting mechanism. However, part of the C-terminal coiled-coil region of ODF2 is also important in centrosomal/ciliary targeting and fiber formation presumably by supporting self-association and the formation of higher-order structures.