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Fig. 5. SAX-3 is expressed in a subset of neuroblasts and neurons that express
VAB-1. (A) Extrachromosomal arrays carrying SAX-3/Robo in a sax-3
background have rescuing activity. We scored for rescue of the sax-3
embryonic lethality and notched-head phenotype (top right). The transgenic
lines restore SAX-3 activity in neuroectoblast (F25B3.3::SAX-3),
epithelial cells (ajm-1::SAX-3) or all SAX-3 tissues (SAX-3 mini gene
and SAX-3::GFP). By contrast, the odr-1::RFP transgenic marker had no
rescuing activity. Note that the ajm-1::SAX-3 did not rescue the
notched-head phenotype. Complete rescue is not expected, as these transgenic
animals carry an extrachromosomal array that is randomly lost during cell
divisions, therefore not all animals carry the extrachromosomal array. Error
bars indicate s.e.m. from at least three broods; n, total number of
embryos scored. Asterisks indicate transgenic animals with significantly less
embryonic lethality or notched heads than sax-3 animals
(t-test, P<0.001). Scale bar: 20 µm. (B) SAX-3 is
expressed in neurons and in epidermal cells during epidermal ventral
enclosure. SAX-3::GFP fluorescence is observed in many neurons (top) and is
similar to VAB-1 expression. SAX-3::GFP is also expressed in epidermal cells
(bottom). (C) VAB-1 and SAX-3 are co-expressed in some neuroblasts and neurons
during development. Three different stages are shown: 100-200 cells (top),
pre-ventral enclosure (middle) and comma stage (bottom). Double immunostaining
with anti-VAB-1 (red) and anti-GFP (green) was used to visualize the
co-localization of VAB-1 and SAX-3. VAB-1 and SAX-3 are expressed in similar
cells but their expression patterns are not identical, consistent with these
two receptors functioning together in some cells but also having independent
roles during development.
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