Neurula rotation determines left-right asymmetry in ascidian tadpole larvae

Kazuhiko Nishide, Michio Mugitani, Gaku Kumano, Hiroki Nishida

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Tadpole larvae of the ascidian Halocynthia roretzi show morphological left-right asymmetry. The tail invariably bends towards the left side within the vitelline membrane. The structure of the larval brain is remarkably asymmetric. nodal, a conserved gene that shows left-sided expression, is also expressed on the left side in H. roretzi but in the epidermis unlike in vertebrates. We show that nodal signaling at the late neurula stage is required for stereotypic morphological left-right asymmetry at later stages. We uncover a novel mechanism to break embryonic symmetry, in which rotation of whole embryos provides the initial cue for leftsided expression of nodal. Two hours prior to the onset of nodal expression, the neurula embryo rotates along the anteriorposterior axis in a counterclockwise direction when seen in posterior view, and then this rotation stops when the left side of the embryo is oriented downwards. It is likely that epidermis monocilia, which appear at the neurula rotation stage, generate the driving force for the rotation. When the embryo lies on the left side, protrusion of the neural fold physically prevents it from rotating further. Experiments in which neurula rotation is perturbed by various means, including centrifugation and sandwiching between glass, indicate that contact of the left epidermis with the vitelline membrane as a consequence of neurula rotation promotes nodal expression in the left epidermis. We suggest that chemical, and not mechanical, signals from the vitelline membrane promote nodal expression. Neurula rotation is also conserved in other ascidian species.

Original languageEnglish
Pages (from-to)1467-1475
Number of pages9
JournalDevelopment
Volume139
Issue number8
DOIs
Publication statusPublished - 2012 Apr 15
Externally publishedYes

Keywords

  • Ascidians
  • Brain asymmetry
  • Left-right asymmetry
  • Neurula rotation
  • Nodal

ASJC Scopus subject areas

  • Molecular Biology
  • Developmental Biology

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