In our effort to identify testis-specific genes we found Fank1, which encodes a 
protein containing a fibronectin type III domain in the amino terminus and five 
ankyrin repeats in its carboxyl terminus. FANK1 displays a high degree of 
sequence conservation in 11 vertebrate species during evolution. Bioinformatic 
and experimental analyses revealed that Fank1 was exclusively expressed in the 
testis in both mice and humans. Fank1 mRNA was expressed in mid to late 
pachytene spermatocytes as well as spermatids in steps 1-14. FANK1 protein was 
localized in the nuclei of the same cells within the seminiferous epithelium. 
Consistent with its nuclear localization, a gene ontology analysis suggests that 
FANK1 has a DNA binding activity and thus may function as a transcription 
factor. Given the highly restricted expression of FANK1, it may have a role in 
regulating gene expression in the transition from the meiotic phase to the 
haploid phase during spermatogenesis.