Marine Biology

, Volume 143, Issue 6, pp 1151–1160 | Cite as

Acrosome differentiation and the acrosome reaction in ascidian spermatozoa: Ascidiella aspersa and Ascidia mentula with some implications for tunicate phylogeny

  • M. FukumotoEmail author
  • O. Zarnescu
Research Article


The spermatozoa of both Ascidiella aspersa and Ascidia mentula have architectural features characteristic of ascidian spermatozoa that have previously been described. They have an elongated head (7 µm long for A. aspersa and 4 µm long for A. mentula), a single mitochondrion that is applied laterally to the nucleus and lacks a midpiece. The acrosome of A. aspersa spermatozoa is a flattened vesicle, about 200 nm×100 nm×40 nm (length, width and height). The acrosome of A. mentula spermatozoa consists of multiple vesicles; they are about 50 nm×50 nm×40 nm (length, width and height). During spermiogenesis in both species, several proacrosomal vesicles (50–70 nm in diameter) appear in a blister at the future apex of the spermatid. In A. aspersa, these vesicles fuse with each other to form a single acrosomal vesicle, while in A. mentula these vesicles do not fuse with each other, and form multiple acrosomal vesicles. In A. aspersa spermatozoa, calcium ionophore A23187 induces the acrosome reaction in which membrane fusion between the acrosomal apical membrane and the overlying sperm plasma membrane occurs along the peripheral margin of the acrosome, resulting in the release of a hybrid, membrane-bound, small vesicle. In A. mentula, multiple acrosomal vesicles disappear by releasing small vesicles after treatment with the calcium ionophore A23187; this also appears to be an acrosome reaction. This paper discusses the way in which acrosome structure and function may have changed during the evolution of the Tunicata.


Acrosome Reaction Sperm Head Perivitelline Space Acrosomal Vesicle Early Spermatid 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The authors are most grateful to Professor G. Freeman, of the University of Texas at Austin, for his valuable suggestions and for reading the manuscript. The author (M.F.) is indebted to Professor J.-O. Stroemberg, the director of the Kristineberg Marine Research Station (KMRS), Fiskebackskil, Sweden, and to Dr. Bishop of the Marine Biological Association, U.K., for providing research facilities. This work was carried out partly at the Kristineberg Marine Research Station (KMRS) of the University of Goteborg, during the summer of 1999, and at the Marine Biological Association, U.K., during the summer of 2000. The author (O.Z.) was financially supported as a fellow of the Romania–Japan Exchange Program under the auspices of the Japanese Society for Promoting Sciences (JSPS) during the summer of 2001.


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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  1. 1.Division of Cell Function, Graduate School of Natural SciencesNagoya City UniversityNagoyaJapan
  2. 2.Faculty of BiologyUniversity of BucharestBucharestRomania

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