Gastrulation is the first major morphogenetic event during animal embryogenesis. Ascidian gastrulation starts with the invagination of 10 endodermal precursor cells between the 64- and late 112-cell stages. This process occurs in the absence of endodermal cell division and in two steps, driven by myosin-dependent contractions of the acto-myosin network. First, endoderm precursors constrict their apex. Second, they shorten apico-basally, while retaining small apical surfaces, thereby causing invagination. The mechanisms that prevent endoderm cell division, trigger the transition between step 1 and step 2, and drive apico-basal shortening have remained elusive. Here, we demonstrate a conserved role for Nodal and Eph signalling during invagination in two distantly related ascidian species, Phallusia mammillata and Ciona intestinalis. Specifically, we show that the transition to step 2 is triggered by Nodal relayed by Eph signalling. Additionally, our results indicate that Eph signalling lengthens the endodermal cell cycle, independently of Nodal. Finally, we find that both Nodal and Eph signals are dispensable for endoderm fate specification. These results illustrate commonalities as well as differences in the action of Nodal during ascidian and vertebrate gastrulation.
A Nodal/Eph signalling relay drives the transition from apical constriction to apico-basal shortening in ascidian endoderm invagination
Current address: EMBL, Meyerhofstrasse 1, D-69117 Heidelberg, Germany
Current address: Multicellular Organization Laboratory, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka 411-8540, Japan
Current address: Institute of Research on Cancer and Aging of Nice, CNRS, UCA, 06000 Nice, France
Currently Viewing Accepted Manuscript - Newer Version Available
Ulla-Maj Fiuza, Takefumi Negishi, Alice Rouan, Hitoyoshi Yasuo, Patrick Lemaire; A Nodal/Eph signalling relay drives the transition from apical constriction to apico-basal shortening in ascidian endoderm invagination. Development 2020; dev.186965. doi: https://doi.org/10.1242/dev.186965
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