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M. Gatti - The role of membrane trafficking in Drosophila cytokinesis
strict fully during the course of furrow ingression.
Consistent with an essential role for membrane trafficking,
cytokinesis during male meiosis is blocked by
the Golgi trafficking inhibitor brefeldin A (BFA). A
Bru-GFP fusion protein localizes to Golgi organelles
with a substantial amount dispersed throughout the
cytoplasm as well. In post-meiotic spermatids, Bru
also localizes to the acroblast, a developmentally regulated
Golgi derivative. Acroblasts fail to form in bru
mutant spermatids, implying a requirement for
TRAPPII in coordinating the organization of Golgi
membranes during acroblast formation. bru genetically
interacts with Rab11, which encodes a small
GTPase that regulates late stages of membrane trafficking,
and with the phosphatidylinositol 4-kinase β
(PI4Kβ)-encoding gene four wheel drive (fwd).
Consistent with this, localization of Rab11 protein to
the cleavage furrow of male meiotic cells requires
wild-type function of bru. The genetic interactions
between the Drosophila genes encoding Bru, PI4Kβ,
and Rab11 are consistent with the known genetic relationships
between their orthologs in budding yeast,
suggesting that membrane trafficking processes that
are essential to the growth and viability of budding
yeast support cleavage furrow ingression during male
meiosis in Drosophila.
Zw10 is required for cytokinesis with a role in
membrane addition during cleavage furrow
ingression
ZW10, along with the other member of the conserved
Rod, Zwilch, Zw10 (RZZ) complex, is
required for proper functioning of the mitotic spindle
assembly checkpoint (SAC). Recent studies in
mammalian cells have shown that Zw10 forms a
complex with syntaxin-18 and is required for the
association of dynein with Golgi membranes, with
reduced levels of Zw10 resulting in disruption of
ER to Golgi transport. We have found that the male
meiotic divisions of zw10 mutants display defects in
cytokinesis, where the acto-myosin ring forms and
begins to ingress but then regresses. Surprisingly,
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this cytokinesis failure is observed only in zw10
mutants even though all three members of the RZZ
complex localize across the mid-zone of the spindle
envelope during telophase. In zwilch and rod
mutants Zw10 no longer localizes to the spindle
envelope mid-zone but concentrates in the ER suggesting
an involvement of Zw10 in the ER-Golgi
membrane traffic required for cytokinesis. Although
no defects were detected in the structure of ER or
Golgi stacks, acroblast formation is defective in
zw10 mutants. These results suggest Zw10, besides
its well-known role in the SAC machinery, is also
involved in membrane dynamics during cytokinesis
and acroblast formation.
Perspectives
We plan to continue our work on Rab1, the Exocist
complex components Exo84 and Sec8 and the
Drosophila ortholog of PACS-1 encoded by smeagol
(sgo). We believe that the analysis of the role of these
proteins during spermatocyte cytokinesis will help
unravel the mechanism of membrane addition to the
cleavage furrow, and the relationships between membrane
traffic and acto-myosin ring constriction.
Selected publications
Giansanti MG, Belloni G, Gatti M. Rab11 is
required for membrane trafficking and actomyosin
ring constriction in meiotic cytokinesis of Drosophila
males. Mol Biol Cell 2007, 18:5034-47.
Giansanti MG, Bucciarelli E, Bonaccorsi S, Gatti
M. Drosophila Spd-2 is an essential centriole component
required for PCM recruitment and astral microtubule
nucleation. Curr Biol. 2008, 18:303-9.
Szafer-Glusman E, Giansanti MG, Nishihama R,
Pringle J, Gatti M, Fuller MT. Specialized lipids are
required to couple actomyosin ring to the plasma
membrane during meiotic cytokinesis in Drosophila
males. Curr Biol. 2008, 23:1426-31.