These factors respond to the differential stabilization
of β-catenin along the primary body axis, triggered by
Wnt signaling [28,29]. In particular, six3 and foxq2 have
been shown to negatively respond to Wnt signaling in a
complex sequence of patterning events [28,29]. These factors
specify apical territory around the apical pole [27,30].
For the first time, the conserved regional expression of
similar sets of transcription factors provides a molecular
framework for the comparison of larval cell types and
tissues and thus important clues to larval body plan and
apical organ evolution.