Identification and Characterization of Human VCY2-Interacting Protein: VCY2IP-1, a Microtubule-Associated Protein-Like Protein

VCY2 is a testis-specific protein that locates in a frequently deleted azoospermia factor c region on chromosome Yq. Although its genomic structure has been characterized, the function of VCY2 is still unknown. To gain insight regarding the likely function of VCY2, we investigated the proteins that interact with VCY2 using the yeast two-hybrid system. We identified a novel VCY2 interaction partner, named VCY2IP-1, that encodes an open reading frame of 1059 amino acids. The amino acid sequence of VCY2IP-1 shows 59.3% and 41.9% homology to two human microtubule-associated proteins (MAPs), MAP1B and MAP1A, respectively. VCY2IP-1 has an extensive homology to the N-terminus and C-terminus regions of MAP1B and MAP1A, placing it within a large family of MAPs. We mapped VCY2IP-1 to chromosome 19p13.11. The VCY2IP-1 gene spans 15 kilobases (kb) and consists of seven exons. Northern blot analysis identified a single, intense band of approximately 3.2-kb VCY2IP-1 transcript, predominantly expressed in human testis. In situ hybridization of human testicular sections showed the localization of VCY2IP-1 transcripts in germ cells, and reverse transcription-polymerase chain reaction analysis demonstrated the presence of VCY2 and VCY2IP-1 transcripts in human ejaculated spermatozoa. Our expression data support the involvement of VCY2 and VCY2IP-1 in spermatogenesis. Based on the high homology of VCY2IP-1 with MAPs, we propose the involvement of VCY2 in the cytoskeletal network via interaction with VCY2IP-1.