Objective:To explore the dynamic expression and migration of the novel testis- and sperm-specific protein FSCB in mouse spermatogenesis and observe the morphological localization of FSCB on normal and abnormal mouse sperm. Methods: For exactly staging of the mouse tubule sections

Periodic acid-Schiff staining was performed at first

and then the dynamic expression of FSCB on mouse testis and sperm by indirect Immunofluorescence was observed. Results:FSCB is a post meiotic protein initially expressed at step 11(stage Ⅺ)of mouse spermatogenesis in the elongating spermatids

and it’s expresson gradully become stronger and stronger from step 11(stage Ⅺ) through step 15 (stage Ⅵ). It subsequently begin migrate into the flagellar at step 15

and at last totally localize to the sperm flagellar at step 16(stage Ⅷ)accompanied with its disappearing from the cytoplasma of sperm. The exact localization of FSCB on normal sperm is in the flagellar principal piece. Its expression and localization on abnormal sperm was variablely changed:a.No expression on the whole flagellar;b. The expression segment on the flagellar was shift to near the head and become short

suggest this sperm defect middle piece;c. Its distribution on the flagellar showed beads like shape. Conclusion: FSCB is an important constituent protein of the fibrous sheath

is assembled at the surface of fibrous sheath core structure and constitutes the final assembly step of fibrous sheath at the later stages of spermiogenesis. The expression of FSCB in abnormal sperm was significantly changed. The relationship between the abnormal expression of FSCB and the sperm motility need to be further studied.