The presumptive floor plate (notoplate) induces behaviors associated with convergent extension in medial but not lateral neural plate cells of Xenopus

Abstract

In previous work (Elul, T., Keller, R., 2000. Monopolar protrusive activity: a new morphogenic cell behavior in the neural plate dependent on vertical interactions with the mesoderm in Xenopus. Dev. Biol. 224, 3-19; Ezin, A.M., Skoglund, P. Keller, R. 2003. The midline (notochord and notoplate) patterns the cell motility underlying convergence and extension of the Xenopus neural plate. Dev. Biol. 256, 100-114), the midline tissues of notochord and overlying notoplate were found to induce the monopolar, medially directed protrusive activity of deep neural cells. This behavior is thought to drive the mediolateral intercalation and convergent extension of the neural plate in Xenopus. Here we address the issue of whether the notochord, the notoplate, or both is essential for this induction. Our strategy was to remove the notochord, leaving the overlying notoplate intact, and determine whether it alone can induce the monopolar, medially directed cell behavior. We first establish that the notoplate (presumptive floor plate), when separated from the underlying notochord in the early neurula (stages 13-14), will independently mature into a floor plate as assayed three criteria: (1) continued expression of an early marker, sonic hedgehog, and a later, marker, F-spondin; (2) the display of the notoplate/floor plate-specific randomly oriented protrusive activity; (3) the characteristic lack of mixing of cells between the notoplate and lateral neural plate. Under these conditions, in the presence of a mature notoplate/floor plate and in the absence of the notochord, the characteristic monopolar, medially directed behavior occurred, but only locally near the midline. These results show that the notoplate/floor plate capacity to induce the medially directed motility is limited in range, and they suggest that the notochord is necessary for the normally observed longer range induction in lateral neural plate cells. This work helps to further the understanding of molecular and tissue interactions required for convergent extension.

The Tangled Web of Non-Canonical Wnt Signalling in Neural Migration

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PTK7 is essential for polarized cell motility and convergent extension during mouse gastrulation

“…The 90°/270° axis was aligned with the A/P axis of the embryo. The average distribution of protrusions was determined by combining observations for all cells in each defined sector surrounding the PNC, and were analyzed as described previously Ezin et al, 2003;Ezin et al, 2006), using a χ 2 test to determine whether the distribution of protrusive activity was significantly different from random and the 2ai test (Baschelet, 1981;Zar, 1998) to determine whether they were monopolar or bipolar (Ezin et al, 2003). We computed 'preferred directions' of protrusion in a given section of the embryo by comparing the frequency of observed protrusion directions by a cell to that expected by chance, and permutation tests were used to assign a probability to the observed difference.…”

Integrin αV is necessary for gastrulation movements that regulate vertebrate body asymmetry

“…Methods to determine individual DFC orientation and length-width ratio measurements were similar to previous studies (Davidson et al, 2006;Ezin et al, 2006). Half-rose diagrams were generated in six sectors with 30 degree (q) intervals, representing anterior (a) with 0 q, mediolateral axis (ml) with 90 q and posterior (p) with 180 q.…”