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Fig. 1. Straightening and elongation of the notochord. (A,B)
The amphibian (Xenopus) notochord straightens and elongates from the
early (A) to late (B) tailbud stage (anterior is to the left, dorsal at the
top). (C,D) The early tailbud notochord consists of transversely
stacked flattened cells that are the shape of pizza slices (C), which
vacuolate and swell during notochord elongation (D). (E) The notochord
is encased in a sheath of extracellular matrix with an average fiber angle of
54° (fibers shown in green). Isolated intact notochords straighten and
lengthen in solutions of low osmotic strength (gray), and bend and shorten in
solutions of high osmotic strength (black). (F) The cells swell but
notochord morphogenesis is lost when the sheath is enzymatically digested.
(G) The mechanical behavior of fiber-wound hydraulic skeletons has been
studied experimentally by varying the water pressure (P) inside latex tubes,
which were embedded with taffeta fiber windings at varying angles and
suspended in a water bath. (H) Geometric parameters were measured,
including fiber angle, diameter, length, curvature (a/b) and shortening or
elongation (2b). (I,J) Mechanical properties were measured,
including flexural stiffness [the force (F) necessary to produce bending
between two supports; I] and isometric force production in pushing and pulling
(J). (A,B,E-J) Reproduced, with permission, from Koehl et al.
(Koehl et al., 2000).
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