CEP295NL

CEP295NL (also known as DDC8) is a testis-expressed protein that localizes to the tails of mature spermatozoa, where it physically interacts with the axonemal/radial spoke proteins IQUB (Trs4), RSPH3, ODF1, and GSTM1, implicating it in sperm flagellar assembly or motility (PMID:19706271, PMID:36355624). Its interaction with IQUB was confirmed by yeast two-hybrid, co-immunoprecipitation, and in vitro binding assays in mouse testis, and the two proteins co-localize along the sperm tail (PMID:19706271).

1. 2009 Medium

   The first functional link for CEP295NL was established by showing it directly binds the testis-specific protein Trs4 (IQUB homolog) and co-localizes with Trs4 and Rshl-2 on sperm tails, placing this otherwise uncharacterized protein in a flagellar context.

   Evidence Yeast two-hybrid, co-immunoprecipitation, in vitro binding, and immunofluorescence co-localization in mouse testes and spermatozoa

   PMID:19706271

   Open questions at the time

   • No loss-of-function data to determine whether CEP295NL is required for sperm motility or fertility
   • Interaction validated only in mouse; human relevance not directly tested
   • Precise sub-structural localization within the axoneme (e.g., radial spoke head vs. stalk) not resolved
2. 2023 Low

   CEP295NL was placed in a broader protein interaction network by demonstrating yeast two-hybrid interactions with RSPH3, ODF1, and GSTM1 in addition to IQUB, linking it to the radial spoke complex and outer dense fibers of the sperm axoneme.

   Evidence Yeast two-hybrid interaction assay

   PMID:36355624

   Open questions at the time

   • Interactions with RSPH3, ODF1, and GSTM1 detected by yeast two-hybrid only; no reciprocal co-immunoprecipitation or pulldown validation
   • Functional consequence of these interactions on sperm motility or flagellar structure not tested
   • No structural or stoichiometric characterization of the putative complex

• It remains unknown whether CEP295NL is essential for spermatogenesis, sperm motility, or male fertility, and no knockout or patient mutation data exist to define its physiological requirement.
• No gene knockout or knockdown phenotype reported
• No association with human male infertility or ciliopathy established
• Mechanism by which CEP295NL contributes to radial spoke or outer dense fiber function is entirely uncharacterized