Elsevier

Developmental Biology

Volume 456, Issue 1, 1 December 2019, Pages 63-73
Developmental Biology

Interplay between Lefty and Nodal signaling is essential for the organizer and axial formation in amphioxus embryos

https://doi.org/10.1016/j.ydbio.2019.08.006Get rights and content
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Highlights

  • Lefty expression pattern follows essentially that of Nodal after the onset of gastrulation in amphioxus embryos.

  • Lefty mutation expands dorsal/anterior structures in amphioxus.

  • Lefty overexpression disrupts organizer formation, and its knockout expands organizer size.

  • Inhibiting Nodal signaling partially rescues the defects of Lefty mutants.

  • Nodal signaling is required and sufficient for initial Lefty expression in amphioxus embryos.

Abstract

The organizer is an essential signaling center required for axial formation during vertebrate embryonic development. In the basal chordate amphioxus, the dorsal blastopore lip of the gastrula has been proposed to be homologous to the vertebrate organizer. Lefty is one of the first genes to be expressed in the organizer. The present results show that Lefty overexpression abolishes the organizer; the embryos were severely ventralized and posteriorized, and failed to develop anterior and dorsal structures. In Lefty knockouts the organizer is enlarged, and anterior and dorsal structures are expanded. Different from Lefty morphants in vertebrates, amphioxus Lefty mutants also exhibited left-right defects. Inhibition of Nodal with SB505124 partially rescued the effects of Lefty loss-of-function on morphology. In addition, while SB505124 treatment blocked Lefty expression in the cleavage stages of amphioxus embryos, activation of Nodal signaling with Activin protein induced ectopic Lefty expression at these stages. These results show that the interplay between Lefty and Nodal signaling plays an essential role in the specification of the amphioxus organizer and axes.

Keywords

Amphioxus
Embryonic development
Lefty gene
Organizer
Nodal signaling

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