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J. Cell Biol.,
Volume 142, Number 3, August 10, 1998 751-761
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
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.
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.
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