Development 2016 Jan 15;1432:286-97. doi: 10.1242/dev.124503.

Neurogenesis in sea urchin embryos and the diversity of deuterostome neurogenic mechanisms.

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A single origin to the diverse mechanisms of metazoan neurogenesis is suggested by the involvement of common signaling components and similar classes of transcription factors. However, in many forms we lack details of where neurons arise, patterns of cell division, and specific differentiation pathway components. The sea urchin larval nervous system is composed of an apical organ, which develops from neuroepithelium and functions as a central nervous system, and peripheral neurons, which differentiate in the ciliary band and project axons to the apical organ. To reveal developmental mechanisms of neurogenesis in this basal deuterostome, we developed antibodies to SoxC, SoxB2, ELAV and Brn1/2/4 and used neurons that develop at specific locations to establish a timeline for neurogenesis. Neural progenitors express, in turn, SoxB2, SoxC, and Brn1/2/4, before projecting neurites and expressing ELAV and SynB. Using pulse-chase labeling of cells with a thymidine analog to identify cells in S-phase, we establish that neurons identified by location are in their last mitotic cycle at the time of hatching, and S-phase is coincident with expression of SoxC. The number of cells expressing SoxC and differentiating as neurons is reduced in embryos injected with antisense morpholino oligonucleotides to SoxC, SoxB2 or Six3. Injection of RNA encoding SoxC into eggs does not enhance neurogenesis. In addition, inhibition of FGF receptors (SU5402) or a morpholino to FGFR1 reduces expression of SoxC. These data indicate that there are common features of neurogenesis in deuterostomes, and that sea urchins employ developmental mechanisms that are distinct from other ambulacraria.

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Genes referenced: fgf fgfr3 LOC100887844 LOC115919910 pou1f1 six6 sox14 sox4
???displayArticle.antibodies??? LOC576570 Ab1 hnf6 Ab1 nkx2-1 Ab1 pou1f1 Ab1 sox14 Ab1 sox4 Ab1 sox4 Ab2
???displayArticle.morpholinos??? fgfr3 MO1 pou1f1 MO1 pou1f1 MO2 six6 MO1 sox4 MO1 sox4 MO2 sox4 MO3