Copyright 2002 by the Genetics Society of America
Mutations in the midway Gene Disrupt a Drosophila Acyl Coenzyme A:
Michael Buszczak,* Xiaohui Lu,†William A. Segraves,* Ta Yuan Chang†and Lynn Cooley‡,1
*Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103,†Department of
Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755 and‡Departments of Genetics and
Cell Biology, Yale School of Medicine, New Haven, Connecticut 06520-8005
Manuscript received November 16, 2001
Accepted for publication January 28, 2002
During Drosophila oogenesis, defective or unwanted egg chambers are eliminated during mid-oogenesis
by programmed cell death. In addition, final cytoplasm transport from nurse cells to the oocyte depends
upon apoptosis of the nurse cells. To study the regulation of germline apoptosis, we analyzed the midway
mutant, in which egg chambers undergo premature nurse cell death and degeneration. The midway gene
encodes a protein similar to mammalian acyl coenzyme A: diacylglycerol acyltransferase (DGAT), which
converts diacylglycerol (DAG) into triacylglycerol (TAG). midway mutant egg chambers contain severely
reduced levels of neutral lipids in the germline. Expression of midway in insect cells results in high levels
of DGAT activity in vitro. These results show that midway encodes a functional DGAT and that changes
in acylglycerol lipid metabolism disrupt normal egg chamber development in Drosophila.
mental mechanisms of development including stem cell
munication, cytoskeletal regulation, and signaling path-
ways (Spradling 1993; Van Buskirk and Schu ¨pbach
ated within each egg chamber that control the co-
ordinated activities of the somatic follicle cells and the
germline nurse cells and oocyte. In addition to egg
chamber-autonomous information, the progression of
oogenesis is influenced by environmental factors such
as food availability. Stage 8 of oogenesis, which is just
prior to the initiation of vitellogenesis, is particularly
sensitive to environmental conditions. Underfed fe-
males accumulate many previtellogenic egg chambers
and produce few if any mature eggs. Stage 8 may also be
a mid-oogenesis checkpoint for monitoring general egg
chamber health; stage 8 egg chambers in wild-type fe-
The removal of defective or doomed egg chambers at
stage 8 could allow the female to conserve the energy
required for vitellogenesis. The mechanism by which
egg chambers are selected to die during mid-oogenesis
is largely unknown, but recent findings point to the
involvement of the ecdysone signaling hierarchy. Dis-
ruption of dare, a gene encoding an enzyme required
ESEARCH on Drosophila oogenesis has led to nu-
merous advances in our understanding of funda-
for steroidogenesis, the ecdysone receptor (EcR), and E75,
an ecdysone early response gene, all cause the develop-
mentalarrestandsubsequentdegeneration of egg cham-
bers during stage 8. It is possible that this hormone
response pathway is a link between environmental con-
ditions and oogenesis progression as is the case in mos-
Cell death also plays an essential role in the develop-
ment of every Drosophila egg. During oogenesis, the
15 nurse cells of each egg chamber are dedicated to
the synthesis of maternal components, which are trans-
ring canals (Mahajan-Miklos and Cooley 1994a). Sev-
the nurse cells to the oocyte during the first 10 stages
stage 11, the nurse cells contract to force their remaining
cytoplasm into the oocyte, resulting in the rapid growth
of the oocyte. During stage 10, nurse cells prepare for
fast cytoplasm transport with a massive rearrangement
of filamentous actin to form arrays of actin bundles
surrounding each nucleus. Actin bundle formation is
followed by nurse cell nuclear membrane permeabiliza-
tion and nurse cell contraction (Matova et al. 1999).
Once the nurse cells have successfully transferred their
cytoplasm into the oocyte, the nurse cell remnants are
cleared from the egg chamber by apoptosis (Cavaliere
et al. 1998; Foley and Cooley 1998). Several lines of
evidence suggest that programmed cell death does not
simply follow rapid transport but actually serves to trig-
ger this morphological event. For instance, electron mi-
croscopy and the use of molecular markers show that
nurse cells exhibit symptoms of apoptosis before the
Sequence data from this article have been deposited with the
EMBL/GenBank Data Libraries under accession nos. AF468649 and
1Corresponding author: Department of Genetics, Yale University
Medical School, 333 Cedar St., P.O. Box 208005, New Haven, CT
Genetics 160: 1511–1518 (April 2002)
1518 M. Buszczak et al.
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Female sterile mutations
Apoptosis in late stage Drosophila
The osmolarity of adult
Control of oocyte matu-
Nile red: a
The villin-like protein
Versatility in signalling:
Requirement for DCP-1 caspase
Cytoskeleton of the Dro-
Communicating editor: T. Schu ¨pbach