Fez function is required to maintain the size of the animal plate in the sea urchin embryo

Abstract

SUMMARYPartitioning ectoderm precisely into neurogenic and non-neurogenic regions is an essential step for neurogenesis of almost all bilaterian embryos. Although it is widely accepted that antagonism between BMP and its inhibitors primarily sets up the border between these two types of ectoderm, it is unclear how such extracellular, diffusible molecules create a sharp and precise border at the single-cell level. Here, we show that Fez, a zinc finger protein, functions as an intracellular factor attenuating BMP signaling specifically within the neurogenic region at the anterior end of sea urchin embryos, termed the animal plate. When Fez function is blocked, the size of this neurogenic ectoderm becomes smaller than normal. However, this reduction is rescued in Fez morphants simply by blocking BMP2/4 translation, indicating that Fez maintains the size of the animal plate by attenuating BMP2/4 function. Consistent with this, the gradient of BMP activity along the aboral side of the animal plate, as measured by pSmad1/5/8 levels, drops significantly in cells expressing Fez and this steep decline requires Fez function. Our data reveal that this neurogenic ectoderm produces an intrinsic system that attenuates BMP signaling to ensure the establishment of a stable, welldefined neural territory, the animal plate.

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

“…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.…”

“…In the sea urchin embryo, six3 and foxq2 are the first ANE regulatory genes expressed in the presumptive ectoderm and both transcription factors act as cardinal regulators of ANE territory specification (Wei et al, 2009;Yaguchi et al, 2008Yaguchi et al, , 2011Yaguchi et al, , 2010. Similar to other deuterostome embryos, six3 and foxq2 initially exhibit pan-ectodermal expression, but then their expression is progressively restricted to a territory around the anterior pole (Wei et al, 2009;Yaguchi et al, 2008).…”

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

“…2E–H, asterisk). Next, we compared distributions of zfhx1/z81 and fez , forebrain embryonic zinc finger , which we recently reported as being expressed in the entire animal plate during blastula stages and subsequently in serotonergic neurons and their precursors (Yaguchi et al, 2011). When the blastula-stage expression of fez begins to fade and is progressively replaced by stronger signals in a few individual cells in the animal plate region at mid-gastrula stage (Fig.…”

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

“…It is reported that SoxC cells co-express Delta (Wei et al, 2016) and that treatment with DAPT, an inhibitor of Notch signaling, or a Delta morpholino results in the formation of clusters of neurons Wei et al, 2009;Yaguchi et al, 2011). This suggests that Notch signaling occurs subsequent to the final cell division and that the division is asymmetric, at least in the distribution of molecular components.…”