Аннотация:Visceral organs of vertebrates positioned in a specific left-right asymmetric way.
The most supported theory about mechanisms of body plan symmetry breakage links
establishment of left-right asymmetry with directed extracellular fluid flow, generated
by mono-ciliated cells in the so-called left-right organizer (LRO). LRO structures were
found in various taxa across of vertebrates, which assume cilia-based mechanism of body
symmetry breakage is conservative. One major question remained unanswered: where and
when in evolution this mechanism was evolved. For our studies, we chose echinoderms,
the basal Deuterostome animals and sister group to Chordata. It was shown that cilia in sea
urchin archenteron (LRO homolog) during gastrulation play a crucial role in the spatial
positioning of Nodal signaling. We use descriptive approaches to characterize differences
in the LRO organization during development of three echinoderms: Paracentrotus lividus,
Strongylocentrotus pallidus and Asterias rubens. The most striking differences we found
between sea urchins and sea stars. We revealed that they have significantly different
dynamics of the cilia formation in the archenteron. At the beginning of gastrulation of
the A.rubens, the vegetal plate does not lose cilia as it happens in sea urchins but starts
to invaginate with outer surface cilia. Surprisingly, the length of these cilia exceeds the
diameter of archenteron. And apparently, such lengths of the cilia are not able to generate
directional fluid flow. Our ultrastructural data let us suggest the absence of dynein arms
in the structure of these cilia, and accordingly their motility. The expression patterns of
motile cilia markers have been analyzed.