How does Nodal controls nervous system asymmetry?

What is it about?

The role of Nodal signalling in nervous system asymmetry is still poorly understood. In this review, we discuss how asymmetric Nodal signalling controls the ontogeny of nervous system asymmetry using a comparative developmental perspective. We show that asymmetries of the nervous system under the developmental control of asymmetric Nodal signalling are widespread across Bilateria. We emphasise that the function of Nodal signalling in the development of asymmetries is strongly context-dependent and that bilaterally paired and midline-unpaired structures can behave differently under the influence of asymmetric Nodal signalling. Using examples from ascidians and fishes, we propose a conceptual framework for the analysis of Nodal function in L – R asymmetry that can be applied not only to nervous system asymmetries but also to cases of body and visceral organ asymmetry under the control of asymmetric Nodal signalling.

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Why is it important?

We propose a conceptual framework to dissect the developmental function of Nodal as "asymmetry inducer" and "laterality modulator" in the nervous system, which can be used to study other types of body and visceral organ asymmetries. Using insights from developmental biology, we also present novel evolutionary hypotheses on how Nodal led the evolution of directional asymmetry in the brain, with a particular focus on the epithalamus.

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