Fibrous Sheath CABYR Binding Protein (FSCB)

Antibodies were raised to a truncated version of the mouse protein, whose full-length version was predicted to be 1,074 amino acids. By database analysis, Li et al. (2007) identified human FSCB, which encodes a deduced 825-amino acid protein. Northern blot analysis of mouse tissues detected a 3.5-kb testis-specific Fscb transcript.

Fscb is first expressed in the elongating spermatids during spermatogenesis. Later in spermatogenesis it is found in the flagellum where it was shown to localize to a cortical layer at the surface of the ribs and longitudinal columns of the fibrous sheath. FSCB may be involved in later stages of fibrous sheath assembly. Like CABYR, FSCB is a calcium-binding protein, and both recombinant and native FSCB are phosphorylated by protein kinase A (PKA).