Takashi Mikawa, Alisa M. Poh, Kristine A. Kelly, Yasuo Ishii, David E. Reese
Figure 8. Potential role of midline cell death in laterality regulation. A: Left-sided expression of a laterality gene Nodal. B: Normal right-sided heart looping. C: Bilateral expression of Nodal, giving rise to randomization of left-right asymmetry, including heart looping. D: Left-sided heart looping induced by inhibition of streak midline cell death with a caspase antagonist (modified from Kelly et al.,). E: Physical barrier model of midline cell death in laterality regulation during early gastrulation. L, left; R, right.
Et la chiralité est sauve !
The primitive streak is the organizing center for amniote gastrulation. It defines the future embryonic midline and serves as a conduit of cell migration for germ layer formation. The migration patterns of endodermal and mesodermal precursors through the streak have been studied in great detail. Additional new breakthroughs recently have revealed the cell biological and molecular mechanisms that govern streak induction and patterning. These findings include (1) identification of the ontogeny and inductive signals of streak precursors, (2) the potential cellular mechanism of streak extension, and (3) the molecular and functional diversification along the anterior-posterior and mediolateral axes within the primitive streak. These findings indicate that amniote embryos initiate gastrulation by using both evolutionarily conserved and divergent mechanisms. The data also provide a foundation for understanding how the midline axis is defined and maintained during gastrulation of the amniotes.
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