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Fig. 1. Endoderm is required for the neurogenesis and survival of EB placodes.
Zebrafish embryos injected with a morpholino against cas (A,C,D,
right) or ngn1 (B, right) and uninjected controls (A-D, left) were
collected at various time points and processed for in-situ hybridization with
ngn1, phox2a and phox2b riboprobes, immunolabeling with Zn-5
or Hu antibody, or TUNEL assay. All whole-mount panels show lateral views.
Anterior is left. (A) Glossopharyngeal and small vagal placodes and ganglia
are absent, while facial and large vagal placodes and ganglia are
significantly reduced (arrows) after cas MO injection. Endodermal
pouches are completely absent in cas morphants (Zn-5, white
arrowheads). (B) phox2a and phox2b expression is absent in
ngn1 morphants. phox2b-positive enteric neuronal precursors
(arrow) were not affected by injection of ngn1-MO. (C) Transverse
sections through the vagal placode revealed ectodermal expression of
ngn1 (arrowheads), indicating that the remaining EB neurons in
cas morphants derived from the placodes. (D) Endoderm is important
for survival of the EB placode cells. Transverse section through the facial
placode revealed TUNEL-positive cells in the cas morphants
(arrowheads). Scale bars: 50 µm. a, acoustic ganglion; al, anterior lateral
line ganglion; e, eye; f, facial placode or ganglion; g, glossopharyngeal
placode or ganglion; pl, posterior lateral line placode or ganglion; t,
trigeminal ganglion; v, vagal placode or ganglion.
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