THE HOMOLOGY OF CORTICAL MICROTUBULES IN PLATYHELMINTH SPERMATOZOA - A COMPARATIVE IMMUNOCYTOCHEMICAL STUDY OF ACETYLATED TUBULIN

Spermatozoa of certain acoels, a group of primitive Platyhelminthes, a nd spermatozoa of the most derived Platyhelminthes, the Cercomeridea ( parasitic Platyhelminthes), show a general morphological resemblance i n that they are long filiform cells with two incorporated axonemes and longitudinal cortical microtubules. A possible way to test the homolo gy of these cortical microtubules in the different groups is to analyz e the presence/absence of post-translational modifications of tubulin. An indirect immunofluorescence study showed that the doublet microtub ules of the sperm axonemes are labelled by an anti acetylated-alpha-tu bulin antibody in all groups, irrespective of the axoneme pattern (9 0, 9 + 2 and non-trepaxonematan 9 + ''1'' in various acoels, and trep axonematan 9 + ''1'' of the temnocephalid Troglocaridicola sp., the di genean Echinostoma caproni and the monopisthocotylean monogenean Pseud odactylogyrus sp.). Significant differences are found in the sperm cor tical microtubules: they are acetylated in the acoel Actinoposthia bek lemischevi, but not in the digenean E. caproni and the temnocephalid T roglocaridicola sp. These results suggest that the sperm cortical micr otubules of the acoels are not homologous with the morphologically sim ilar elements found in the higher Platyhelminthes. (C) 1998 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd. All ri ghts reserved.