FGF3 in the floor plate directs notochord convergent extension in theCionatadpole

Abstract

Convergent extension (CE) is the narrowing and lengthening of an embryonic field along a defined axis. It underlies a variety of complex morphogenetic movements, such as mesoderm elongation and neural tube closure in vertebrate embryos. Convergent extension relies on the same intracellular molecular machinery that directs planar cell polarity (PCP) in epithelial tissues, including non-canonical Wnt signaling components. However, it is not known what signals coordinate CE movements across cell fields. In the simple chordate Ciona intestinalis, the notochord plate consists of just 40 cells, which undergo mediolateral convergence (intercalation) to form a single cell row. Here we present evidence that a localized source of FGF3 in the developing nerve cord directs notochord intercalation through non-MAPK signaling. A dominant-negative form of the Ciona FGF receptor suppresses the formation of polarized actin-rich protrusions in notochord cells, resulting in defective notochord intercalation. Inhibition of Ciona FGF3 activity results in similar defects, even though it is expressed in an adjacent tissue: the floor plate of the nerve cord. In Xenopus mesoderm explants, inhibiting FGF signaling perturbs CE and disrupts membrane localization of Dishevelled (Dsh), a key regulator of PCP and CE. We propose that FGF signaling coordinates CE movements by regulating PCP pathway components such as Dsh.

Distinct Xenopus Nodal ligands sequentially induce mesendoderm and control gastrulation movements in parallel to the Wnt/PCP pathway

“…We co-expressed a Dsh-GFP fusion protein with a membrane-bound form of the fluorescent protein mCherry in the mesoderm, and treated early gastrula embryos with SB-505124 or SU5402. As expected, SU5402 prevented recruitment of Dsh-GFP at the membrane of mesoderm cells (Shi et al, 2009). By contrast, Dsh-GFP was present at the membrane of SB-505124-treated non-gastrulating embryos (Fig.…”

FGF-dependent midline-derived progenitor cells in hypothalamic infundibular development

“…The finding that FGF signalling from ventral midline cells may sustain proliferative properties in adjacent lateral fp cells might be relevant in other regions of the neuraxis. SoxB1 gene expression is maintained in lateral fp cells that show sustained proliferation (Pevny et al, 1998), whereas expression of FGFs, namely Fgf3 and the isoform altFgf2, has been noted in ventral midline fp cells in the posterior neuraxis (Shi et al, 2009;Borja et al, 1996).…”

Divergent mechanisms specify chordate motoneurons: evidence from ascidians

“…Except for BMP2/4, all expression patterns have been described previously Hudson et al, 2007;Hudson and Yasuo, 2005;Ikuta and Saiga, 2007;Imai et al, 2004;Imai et al, 2006;Shi et al, 2009;Takamura et al, 2002) (http://ghost.zool.kyoto-u.ac.jp). In situ hybridisation was carried out as described previously (Hudson and Yasuo, 2006;Wada et al, 1995).…”