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. Author manuscript; available in PMC: 2013 Mar 1.
Published in final edited form as: Dev Biol. 2011 Dec 22;363(1):74–83. doi: 10.1016/j.ydbio.2011.12.024

Figure 8.

Figure 8

Model of the regulatory mechanisms controlling differentiation of serotonergic neurons in the sea urchin embryo. FoxQ2 and Six3 are involved in the specification of the animal plate during early development (1; Yaguchi et al., 2008, 2; Wei et al., 2009). FoxQ2 is required for fez expression and then Fez maintains foxQ2 expression on the aboral side of the animal plate (3; Yaguchi et al., 2011). Both FoxQ2 and Six3 regulate zfhx1/z81 and delta expression and Six3 supports FoxQ2 expression (2). Zfhx1/z81 is required for the expression of tph, which is required for serotonin synthesis, and for synaptotagminB (synB). Delta-Notch signaling limits the number of differentiating neurons by lateral inhibition and Nodal inhibits their development on the oral side of the animal plate. Zfhx1/Z81 suppresses its own expression.