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AMACHER/ELSEVIER$ n, p: L) r5 ]4 H* p
# }- U* P+ S( o* x/ P$ w% HAs slow-twitch muscle cells migrate through fast-twitch muscle precursor cells, they act as morphogenesis tutors, according to Clarissa Henry and Sharon Amacher (University of California, Berkeley, CA).# H& R8 \- V" m6 Y' B3 Y' d0 P' t
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Fast-twitch muscle cells in zebrafish start off life as round blobs but must undergo anterio-posterior elongation to become functional myofibers. Henry and Amacher had noticed that this elongation process spreads in a medial-to-lateral wave, i.e., cells near the midline change shape first.' `3 n- @: }! Y7 K/ P9 v
1 j; K' R% Z: O1 _/ ^. f0 yThe authors first established that elongation required Hedgehog signaling. Transplantation experiments showed, however, that this effect was indirect. To restore fast-twitch elongation in a Hedgehog-signaling mutant, the critical ingredient was wild-type slow-twitch cells not wild-type fast-twitch cells.6 {) [% \7 Y7 D' B7 Z$ ?5 k
7 m; w/ y) o N: p& kIn response to the Hedgehog signal, transplanted slow-twitch cells extended across the anterior–posterior width of a somite and migrated outwards from the notochord. Fast-twitch cells in their wake elongated. The effect could be relayed to other fast-twitch cells as long as the targets were in the same somite. In the wild type there are probably enough migrating cells to contact directly all of the fast-twitch cells.0 N, v6 i h/ a1 n: V9 }( ]6 G
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Future work will show if the slow-twitch cell or its discarded extracellular matrix is acting as a scaffolding for the fast-twitch cell, or if other signals are at work. In other sites of cell migration, such as the developing limb and early embryo, there may be similar drop-offs of differentiation and morphogenesis cues.
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4 F& U0 e) `& c% j5 E+ p1 E7 S$ @6 `Reference:
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Henry, C.A., and S.L. Amacher. 2004. Dev. Cell. 7:917–923.(Ovoid fast muscle cells (white arrow) st) |
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发表于 2009-3-6 08:41
发表于 2015-5-26 16:59
