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Abstract
Cephalopods show a very complex nervous system, particularly derived when compared
to other molluscs. In vertebrates, the setting up of the nervous system depends on
genes such as Shh and Pax6. In this paper we assess Shh and Pax6 expression patterns
during Sepia officinalis development by whole-mount in situ hybridization. In vertebrates,
Shh has been shown to indirectly inhibit Pax6. This seems to be the case in cephalopods
as the expression patterns of these genes do not overlap during S. officinalis development.
Pax6 is expressed in the optic region and brain and Shh in gut structures, as already
seen in vertebrates and Drosophila. Thus, both genes show expression in analogous
structures in vertebrates. Surprisingly, they also exhibit unconventional expressions
such as in gills for Pax6 and ganglia borders for Shh. They are also expressed in
many cephalopods' derived characters among molluscs as in arm suckers for Pax6 and
beak producing tissues, nuchal organ and neural cord of the arms for Shh. This new
data supports the fact that molecular control patterns have evolved with the appearance
of morphological novelties in cephalopods as shown in this new model, S. officinalis.