In vitro induction of crawling in the amoeboid sperm of the nematode parasite, Ascaris suum.

In a highly synchronous process, the immotile spermatids of Ascaris suum extend pseudopods and become rapidly crawling sperm when treated with an extract from the glandular vas deferens of the male under strict anaerobic conditions. Within 9-12 min, a pseudopod develops, elongates rapidly, and exhibits a continuous flow of membrane specializations, the villipodia, from tip toward base. When attached to acid-washed glass, the pseudopod pulls the cell body along at speeds exceeding 70 microns/min. The pseudopod length remains constant while retrograde flow of villipodia proceeds at the same rate as the sperm's forward movement. Cohorts of about 15 villipodia form at the leading edge, move rearward together, and disappear at the junction of pseudopod and cell body. These are the terminations of branched, refringent fibers, which extend the length of the pseudopod. The latter are the fiber complexes that form its cytoskeleton (Sepsenwol et al.: Journal of Cell Biology 108:55-66, 1989). Locomoting cells sometimes change direction when another crawls by and follow each other. When cells are exposed to air, forward movement ceases in a predictable pattern: the forward extension of the leading edge ceases, the pseudopod shortens from the base, and the cell body continues to be pulled forward. These data contribute to a model for Ascaris sperm amoeboid motility in which independent processes of continuous extension at the leading edge and continuous shortening at the base of the pseudopod act to propel the cell forward.