Results
The formation and the rearrangement of the nervous system
during development of a sea cucumber S. japonicus were
analyzed using immunohistochemistry. Embryos and larvae
were staged according to Yoshida et al., 2002. Names of the
larval body parts used in the text are described in Fig. 1.
Differentiation of nerve cells
Positive signals with the antibodies were first observed in the
apical region of the ectodermal epithelium at the late gastrula
stage. Several 1E11-positive cells appeared, and a few of these
cells also reacted positively to anti-serotonin antibody (Figs.
2A–D). No staining with the 1F9 antibody was observed at this
stage (data not shown). The number of immunoreactive cells
increased at the site as development progressed. At the early
auricularia stage, the cells with 1E11 immunoreactivity were
incorporated into the ventral surface of the oral hood (Figs. 2E–
H). Some of these cells also showed serotonergic immunoreactivity
at this stage. Pseudopod-like processes were seen in
some of the 1E11 reacting cells, probably the growing neurites
(Fig. 2I arrows).
Nervous system of the auricularia larva
Mid-auricularia larva possessed prominent 1E11 immunoreactive
nerve tracts along the ciliary bands (Fig. 3A). Flaskshaped
1E11-positive cell bodies were seen lined along the
preoral and postoral (transverse) ciliary bands, with axons
extending into the ciliary band nerve tracts (Fig. 3A inset).
Lateral and slightly posterior to the mouth, a Y-shaped bundle of
1E11-positive neurites were present. This lateral triradial nerve
tract connected the preoral, postoral, and the dorsal ciliary band