Actin and major sperm protein in spermatozoa of a nematode, Graphidium strigosum (Strongylida: Trichostrongylidae).

In most amoeboid cells, the main protein involved in motility is actin. Nematode sperm are an exception, and their amoeboid motility is based on major sperm protein (MSP). We have studied the localization of actin and MSP in spermatids and spermatozoa of Graphidium strigosum (Dujardin, 1845), a species which has elongate male germ cells in which organelles are easily identified. Electrophoreses of G. strigosum sperm proteins indicate that the main protein band, about 15 kDa in molecular weight, is specifically recognized by an anti-MSP polyclonal antibody developed against MSP of Caenorhabditis elegans (Burke and Ward 1983). Actin is present in small quantities. Immunocytochemical observations reveal that actin and MSP have an identical localization in precise areas of the male germ cells. Spermatids are labelled as dots around a central unlabelled zone, and spermatozoa are labelled only at the level of the anterior cap. Observations in G. strigosum are similar to that previously obtained in Heligmosomoides polygyrus (Mansir and Justine 1996). Co-localization of actin and MSP in the anterior cap of the spermatozoon, the region associated with pseudopod production, does not demonstrate directly that actin is involved in amoeboid movements, but shows that the role of actin in the cytoskeleton of nematode sperm should be re-investigated.