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© The Rockefeller University Press, 0021-9525/1998//751 $5.00
The Journal of Cell Biology, Volume 142, Number 3, , 1998 751-761

Regular Articles

Spindle Self-organization and Cytokinesis During Male Meiosis in asterless Mutants of Drosophila melanogaster



Silvia Bonaccorsi, Maria Grazia Giansanti, and Maurizio Gatti

Istituto Pasteur-Fondazione Cenci Bolognetti, Dipartimento di Genetica e Biologia Molecolare, Universita' di Roma La Sapienza, 00185 Rome, Italy

While Drosophila female meiosis is anastral, both meiotic divisions in Drosophila males exhibit prominent asters. We have identified a gene we call asterless (asl) that is required for aster formation during male meiosis. Ultrastructural analysis showed that asl mutants have morphologically normal centrioles. However, immunostaining with antibodies directed either to {gamma} tubulin or centrosomin revealed that these proteins do not accumulate in the centrosomes, as occurs in wild-type. Thus, asl appears to specify a function required for the assembly of centrosomal material around the centrioles.

Despite the absence of asters, meiotic cells of asl mutants manage to develop an anastral spindle. Microtubules grow from multiple sites around the chromosomes, and then focus into a peculiar bipolar spindle that mediates chromosome segregation, although in a highly irregular way.

Surprisingly, asl spermatocytes eventually form a morphologically normal ana–telophase central spindle that has full ability to stimulate cytokinesis. These findings challenge the classical view on central spindle assembly, arguing for a self-organization of this structure from either preexisting or newly formed microtubules. In addition, these findings strongly suggest that the asters are not required for signaling cytokinesis.

Key Words: centrosome • spindle assembly • cytokinesis • male meiosis • Drosophila

Address all correspondence to Silvia Bonaccorsi, Dipartimento di Genetica e Biologia Molecolare, Universita' di Roma La Sapienza, P.le Aldo Moro 5, 00185 Rome, Italy. Tel.: 39-6-49912593; Fax: 39-6-4456866; E-mail: bonaccorsi{at}axcasp.caspur.it

1. Abbreviation used in this paper: EMS, ethyl methane sulfonate.


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