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Fig. 3. Pan-glial misexpression of Mmp1 or Mmp2 blocks motor
axon defasciculation. In each micrograph, two abdominal hemisegments of
stage 17 dissected embryos stained with 
-FasII to label the motor
projections are shown with anterior left and dorsal up. Below each image are
schematics of the observed phenotypes with motor axons in brown and muscles
represented by gray boxes. (A,D) In wild type, axons in ISNb
defasciculate from the ISN and extend dorsally to their synaptic targets.
(B,C,E,F) In repo>Mmp1 and
repo>Mmp2 embryos, ISNb axons fail to defasciculate appropriately
and instead remain tightly bundled together, exhibiting either a `parallel
bypass' (B,E); or a stronger `fusion bypass' phenotype (C,F). In fusion
bypass, ISNb axons fail to separate from ISN axons at their first choice point
and bypass the VLM field. (G,J) In wild type, SNa axons
bifurcate into dorsal and posterior SNa branches and innervate lateral muscle
targets. (H,K) repo>Mmp1 embryos exhibit mild stalls
of the dorsal SNa branch (arrowheads). (I,L)
repo>Mmp2 embryos display strongly truncated dorsal branches
(arrowheads) and mildly stalled posterior branches. Scale bar: 15 µm.
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