Nurit, a novel leucine-zipper protein, expressed uniquely in the spermatid flower-like structure

Spermatozoa formation involves drastic morphological and cellular reconstructions. However, the molecular mechanisms driving this process remain elusive. We describe the cloning of a novel murine spermatid-specific gene, designated nurit, identified in a two-hybrid screen for proteins that binds the Nek1 kinase. Nurit protein harbors a leucine-zipper motif, and two additional coiled-coil regions. The C-terminal coiled-coil domain mediates homodimerization of the protein. Nurit homologues are found in primates, pig and rodents. nurit is transcribed through the elongation stage of the spermatids, but is absent from mature spermatozoa. Interestingly, immunogold electron microscopy revealed that the protein is restricted, from its first detectable appearance, to a unique spermatid organelle called the 'flower-like structure'. The function of this structure is unknown, though it may be involved in transporting proteins designated to be discarded via the residual bodies. Nurit is the first marker of the flower-like structure, and its study may provide an excellent opportunity to dissect the function of this organelle.