The induction of sensory organ placodes, in particular the lens placode, re
presents the paradigm for induction. We show that medaka Sox3 is expressed
in the neuroectoderm and in the placodes of all sensory organs prior to pla
code formation and subsequently in placode-derived tissues. Ectopic Sox3 ex
pression leads to ectopic expression of Pax6 and Eya1 in embryonic ectoderm
and causes ectopic lens and otic vesicle formation. The descendants of cel
ls ectopically expressing Sox3-mRNA contribute to ectopic lens tissue. This
suggests a permissive role for Sox3 in establishing a placodal competence.
In addition, ectopic Sox3 expression leads to the dysgenesis of the endoge
nous sensory organs. Both effects of ectopic Sox3 expression can be separat
ed by ectopic expression of a truncated Sox3 variant depending on its expre
ssion level. Our data suggests that Sox3 is a permissive factor for sensory
placode formation and plays an important role in sensory organ development
. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.