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AMACHER/ELSEVIER
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As 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).
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# ~/ M8 F$ D$ A+ l+ L1 [ Z0 wFast-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.2 s% i9 S0 h4 Q+ y7 V6 U( x
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The 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." i7 t2 | p5 D/ g! E
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In 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." `, o1 y& \' I$ C; j
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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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Reference:/ a# P* N& _* P* K
$ O) Y9 A$ p! X, T. c* jHenry, 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
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