The Nodal signaling pathway controls left-right asymmetric development in amphioxus

Abstract

BackgroundNodal is an important determinant of the left-right (LR) body axis in bilaterians, specifying the right side in protostomes and non-chordate deuterostomes as opposed to the left side in chordates. Amphioxus represents an early-branching chordate group, rendering it especially useful for studying the character states that predate the origin of vertebrates. However, its anatomy, involving offset arrangement of axial structures, marked asymmetry of the oropharyngeal region, and, most notably, a mouth positioned on the left side, contrasts with the symmetric arrangement of the corresponding regions in other chordates.ResultsWe show that the Nodal signaling pathway acts to specify the LR axis in the cephalochordate amphioxus in a similar way as in vertebrates. At early neurula stages, Nodal switches from initial bilateral to the left-sided expression and subsequently specifies the left embryonic side. Perturbation of Nodal signaling with small chemical inhibitors (SB505124 and SB431542) alters expression of other members of the pathway and of left/right-sided, organ-specific genes. Upon inhibition, larvae display loss of the innate alternation of both somites and axons of peripheral nerves and loss of left-sided pharyngeal structures, such as the mouth, the preoral pit, and the duct of the club-shaped gland. Concomitantly, the left side displays ectopic expression of otherwise right-sided genes, and the larvae exhibit bilaterally symmetrical morphology, with duplicated endostyle and club-shaped gland structures.ConclusionsWe demonstrate that Nodal signaling is necessary for establishing the LR embryonic axis and for developing profound asymmetry in amphioxus. Our data suggest that initial symmetry breaking in amphioxus and propagation of the pathway on the left side correspond with the situation in vertebrates. However, the organs that become targets of the pathway differ between amphioxus and vertebrates, which may explain the pronounced asymmetry of its oropharyngeal and axial structures and the left-sided position of the mouth.Electronic supplementary materialThe online version of this article (doi:10.1186/2041-9139-6-5) contains supplementary material, which is available to authorized users.

Cerberus–Nodal–Lefty–Pitx signaling cascade controls left – right asymmetry in amphioxus

“…Cer, Nodal, Lefty, and Pitx are known to be asymmetrically expressed in amphioxus embryos (18)(19)(20)(21), however the relative timing of their expression has yet to be elucidated. We therefore examined whether these genes are spatiotemporally activated in patterns consistent with a regulatory hierarchy.…”

“…We also found that Nodal manipulation fed back on Cer expression, with Alk4/5/7 inhibition inducing ectopic left-sided Cer (as previously reported in ref. 18) and Nodal overexpression inhibiting Cer expression in the first somites (Fig. 2 D and L).…”

“…Other endodermal organs are similarly asymmetric, and somites also show pronounced LR asymmetry. Cer, Nodal, Lefty, and Pitx are asymmetrically expressed in amphioxus, and pharmacological manipulation of the Alk4/5/7 Tgfβ receptor disrupts LR development, suggesting a function for Nodal in amphioxus LR asymmetry (17,18). However, Nodal function has not been directly tested, and it is not known if Pitx regulates LR asymmetric morphology.…”

Nodal signalling and asymmetry of the nervous system

“…In cephalochordates, besides the prominent left-sided asymmetric locations of the mouth and entire pharyngeal region, the arrangement of the bilaterally paired somatic neurons and the peripheral nerves associated with the somites are also asymmetric. Importantly, these asymmetries are preceded and controlled by asymmetric Nodal expression (figure 1a) [10]. In the same animals, an asymmetric funnel-shaped lobe of the right ventral margin of the brain connects with the right-located Hatschek's pit through the infundibulum that descends along the right side of the notochord [11].…”

When and Why Did Brains Break Symmetry?

“…The signaling molecule, Nodal, is involved in the development of asymmetry in vertebrates [35][36][37][38]. Grande and Patel [39] discovered that an orthologue of Nodal is also present in a non-deuterostome, a snail.…”