Zinc finger homeobox is required for the differentiation of serotonergic neurons in the sea urchin embryo

Abstract

Serotonergic neurons differentiate in the neurogenic animal plate ectoderm of the sea urchin embryo. The regulatory mechanisms that control the specification or differentiation of these neurons in the sea urchin embryo are not yet understood, although, after the genome was sequenced, many genes encoding transcription factors expressed in this region were identified. Here, we report that zinc finger homeobox (zfhx1/z81) is expressed in serotonergic neural precursor cells, using double in situ hybridization screening with a serotonergic neural marker, tryptophan 5-hydroxylase (tph) encoding a serotonin synthase that is required for the differentiation of serotonergic neurons. zfhx1/z81 begins to be expressed at gastrula stage in individual cells in the anterior neuroectoderm, some of which also express delta. zfhx1/z81 expression gradually disappears as neural differentiation begins with tph expression. When the translation of Zfhx1/Z81 is blocked by morpholino injection, embryos express neither tph nor the neural marker synaptotagminB in cells of the animal plate, and serotonergic neurons do not differentiate. In contrast, Zfhx1/Z81 morphants do express fez, another neural precursor marker, which appears to function in the initial phase of specification/differentiation of serotonergic neurons. In addition, zfhx1/z81 is one of the targets suppressed in the animal plate by anti-neural signals such as Nodal as well as Delta-Notch. We conclude that Zfhx1/Z81 functions during the specification of individual anterior neural precursors and promotes the expression of tph and synaptotagminB, required for the differentiation of serotonergic neurons.

An anterior signaling center patterns and sizes the anterior neuroectoderm of the sea urchin embryo

“…MO, morpholino. (Yaguchi et al, 2012(Yaguchi et al, , 2008(Yaguchi et al, , 2010. The formation of serotonergic neurons begins during the early pluteus larval stages on the dorsal side of the embryo in a territory around the interface of the inner anterior discoidal domain marked by foxq2 expression and the outer ANE domain marked by the ring of six3 expression (Fig.…”

“…Based on the expression patterns of six3 and foxq2 at the mesenchyme blastula stage (24 hpf ) and the fact that FoxQ2 acts as a cardinal regulator of many cell fates in the central ANE territory (Yaguchi et al, 2012(Yaguchi et al, , 2011(Yaguchi et al, , 2010, we reasoned that FoxQ2 might play a crucial role in establishing the inner and outer ANE domains. To test this hypothesis, we monitored the expression of six3 at the mesenchyme blastula stage in embryos injected with FoxQ2 morpholino oligonucleotides.…”

“…Six3 sits at or near the top of the entire ANE GRN and antagonizes posterior-to-anterior Wnt signaling (Wei et al, 2009). FoxQ2 is necessary for serotonergic neural specification and acts as a cardinal regulator of apical tuft specification in the central ANE subdomain (Yaguchi et al, 2012(Yaguchi et al, , 2010. Remarkably, the ANE positioning mechanism involves much more than the Wnt/β-catenin signaling pathway in the sea urchin.…”

Neurogenic gene regulatory pathways in the sea urchin embryo

“…Although another zinc finger protein, Zfhx/Z81 (Yaguchi et al, 2012), has been shown to be required for the development of serotonergic neurons, and several other transcription factors have been shown to be expressed within them , Z167 is the first factor to be shown to functionally link to the shared core regulatory pathway of Six3→SoxC→Brn1/2/4 that is required for all neurons.…”

“…Homologs of a number of genes implicated in neurogenesis in other systems have been identified that also depend on Six3 for expression (Wei et al, 2009) and the requirement for several has been demonstrated by functional assays, including Zfhx for serotonergic neurons (Yaguchi et al, 2012) and Nkx3.2 for pharyngeal neurons (Wei et al, 2009). Here, we have provided a scaffold pathway for integrating other genes into a GRN for neurogenesis in sea urchin embryos.…”