Exploration of novel mechanisms regulating early cardiomyocyte development by using a differential-display method

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During axis formation in amniotes, posterior and lateral epiblast cells in the area pellucida undergo a counter-rotating movement along the midline to formprimitive streak (Polonaise movements). Using chick blastoderms, we investigated thesignaling involved in this cellular movement in epithelial-epiblast. In cultured posteriorblastoderm explants from stage X-XI embryos, either Lefty1 or Cerberus-S inhibited initialmigration of the explants on chamber slides. In vivo analysis showed that inhibition ofNodal signaling by Lefty1 affected the movement of DiI-marked epiblast cells prior to theformation of primitive streak. In Lefty1-treated embryos without a primitive streak,Brachyury expression showed a patchy distribution. However, SU5402 did not affect themovement of DiI-marked epiblast cells. Multi-cellular rosette, which is thought to beinvolved in epithelial morphogenesis, was found predominantly in the posterior half of theepiblast, and Lefty1 inhibited the formation of rosettes. Three-dimensional reconstruction showed two types of rosette, one with a protruding cell, the other with a ventral hollow.Our results suggest that Nodal signaling may have a pivotal role in the morphogeneticmovements of epithelial epiblast including Polonaise movements and formation of multi-cellular rosette.