MICROTUBULAR SYSTEM DURING SPERMIOGENESIS AND IN THE SPERMATOZOON OF CONVOLUTA-SALIENS (PLATYHELMINTHES, ACOELA) - TUBULIN IMMUNOCYTOCHEMISTRY AND ELECTRON-MICROSCOPY

Spermiogenesis and the spermatozoon were studied in Convoluta saliens, an acoel platyhelminth, by transmission electron microscopy, labellin g of nuclei and immunocytochemistry of tubulin with various antibodies . Spermiogenesis involves formation of a long spermatid shaft containi ng two axonemes. It is established that the nucleus, after a stage of elongation, does not migrate up to the distal extremity of the spermat id, and that the centriolar derivatives are located at the distal extr emity of the shaft. This contrasts with the parasitic Platyhelminthes. The mature spermatozoon, 180 mu m in length, comprises a nuclear regi on, 50 mu m in length, and a cytoplasmic region, with a short region o f overlap. The cytoplasmic region contains two lateral axonemes with a 9 +/- 2 pattern of microtubules, granules of two different sizes, and two rows of longitudinal microtubules in the center. Each row consist s of 5-6 singlet microtubules, with links between them. Whereas the tw o axonemes are labelled by antibodies against alpha, acetylated-alpha, and beta tubulin, the microtubule rows are labelled only by the anti- beta-tubulin antibody. This suggests that acetylation does not occur i n this part of the cytoskeleton, and that the epitope recognized by th e anti-alpha-tubulin antibody (DM1A) is different in these units. Mol. Reprod. Dev. 52:74-85, 1999. (C) 1999 Wiley-Liss, Inc.