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Fig. 6. The action of mau-2 is independent of that of slt-1 to
guide AVM ventrally. (A) AVM was visualized with mec-4::gfp. Anterior
is towards the right, ventral at the bottom. (a) A wild-type AVM axon in which
the axon first projects ventrally and then turns anteriorly. The axon of AVM
fails to migrate ventrally (b-d): the axon of AVM projects anteriorly in
mau-2 and slt-1 single mutants (b), or posteriorly in
mau-2 single mutant (c), and dorsally in mau-2;slt-1 double
mutants and in mau-2(qm160) misexpressing SLT-1 under the
myo-3 promoter (d,e). (e) The axon of AVM projects dorsally (past the
dorsoventral position of the neurone ALM) and, although not in the plane of
focus here, then turns anteriorly, migrating alone for a distance and finally
joining the axon of ALM. A short anterior branch is also present. Arrows and
arrowheads in a-e indicate AVM and ALM, respectively. (B) Phenotype of the
axon of AVM in mau-2;slt-1 double mutants and in
mau-2(qm160) animals misexpressing SLT-1 (kyIs218 and
kyIs209 are integrated myo-3::slt-1 transgenes). Light grey
indicates that the AVM axon projected anteriorly; dark grey, posteriorly;
black, dorsally. The mau-2;slt-1 double mutants exhibit an
enhancement of the ventral guidance defect compared with the single mutants,
and display a novel phenotype (dorsal projection; n=170-300). Error
bars indicate standard error of the proportion. (C) The function of
mau-2 appears to be acting in parallel to those of slt-1 and
unc-6 to guide the axon of AVM. The AVM neurone is shown in the
right-hand panel. Its cell body rests at the boundary between the ventral
muscle quadrant and the lateral hypodermis. The axon of AVM normally projects
ventrally (towards the bottom), along the ventral muscle quadrant, and then
turns anteriorly (towards the right). The broken arrows indicate that the axon
of AVM can project abnormally (anteriorly, posteriorly or dorsally) in some
mutant situations. Loss of function of unc-6, slt-1 or mau-2
results in abnormal anteriorly projecting AVM axons; loss of function of
unc-6 or mau-2 can also result in posteriorly oriented
axons. When the activity of both mau-2 and slt-1 are
altered, the axon of AVM can project dorsally. It appears that three
mechanisms (unc-6-mediated attraction, slt-1-mediated
repulsion and that involving mau-2) are partially redundant to guide
AVM ventrally. Scale bars: 5 µm.
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