Polarization by migration

杨柳

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/ y; }2 `( {' ^/ [+ TThe direction of cell migration may determine the direction of planar polarization, say Hern芍n L車pez-Schier, Jim Hudspeth, and colleagues (Rockefeller University, New York, NY).
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7 P( \% ]7 S  KPlanar polarity controls the polarity across epithelial sheets using components distinct from those that determine apical-basal differences. These planar polarity components have been well-studied but all act to interpret rather than generate the planar polarity signal.
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7 `& b! U  E4 U! M0 K$ X' YMany previous workers studied planar polarity using bristle morphology in flies, but the Rockefeller group set out to study the neuromasts of the lateral line organ in zebrafish〞a system where the planar polarity is vital for the biology. Hair cells in the neuromasts must be precisely aligned so they can use polarized stereociliary bundles to detect the direction of water movement." \! V! I" ^5 E

( }1 g$ m8 C- R2 d# k' w  wL車pez-Schier found that the neuromasts migrated posteriorly in two waves from two primordia. Hair cells derived from the first migrating primordium differentiated soon after being deposited and were fixed in this anterior-posterior orientation even after a much later ventral migration. But the second primordium received a ventral migration signal when it was still immature and was fixed in a perpendicular orientation. This allows the fish to detect water movements in two distinct axes.
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; X/ y% c# e, K+ ^3 EDisruption of the posterior migration cue in mutants and with misexpression altered both migration and polar polarization in equivalent directions. L車pez-Schier thinks that some of the molecules deposited at the front of migrating cells may favor later polarization events., n1 a  @! F, F) z: B3 d% P

6 k$ Z1 `& |9 ^: U2 {- t& o. e  {, nMigration may be a factor in other polarization events such as those occurring during gastrulation. Zebrafish offer a system where the migration can be tracked without the need for dissection. The fish also regenerate neuromasts after ablation, and L車pez-Schier wants to know if proper polarity can also be recovered. If regenerated hair cells, originating from resident or externally supplied stem cells, "are not polarized properly it would be a major problem," he says. In the vestibular organ, for example, randomly oriented hair cells might not work properly and "the animal would feel seasick constantly."+ \* Y5 y5 l9 B; v$ ]7 y

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L車pez-Schier, H., et al. 2004. Dev. Cell. 7:401–412.(Neuromasts polarize in different directi)