Abstract The crawling motility of nematode sperm is driven by the unconventional cytoskeletal protein, Major Sperm Protein (MSP). In developing spermatocytes, MSP assembles on the cytosolic side of Golgi-derived membranous organelles (MOs) in structures called Fibrous Bodies (FBs). These MSP-laden FB-MO complexes facilitate the subsequent segregation of MSP to budding spermatids and away from central residual bodies. Here we identify SPE-55 as a key FB assembly factor.
