First published online February 13, 2009
Journal of Experimental Biology 212, 673-683 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.023481
Skeletal muscle fiber types in the ghost crab, Ocypode quadrata: implications for running performance
Michael J. Perry1,*,
Jennifer Tait1,*,
John Hu1,*,
Scott C. White2 and
Scott Medler1,
1 Department of Biological Sciences, University at Buffalo, Buffalo, NY 14260,
USA
2 Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo,
NY 14260, USA
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Fig. 1. Anatomical organization of the extensor and flexor carpopodite muscles of
the ghost crab. In each figure, the exoskeleton covering the muscles has been
removed to allow an unobstructed view of the muscles. (A) General orientation
of the muscles within a walking leg viewed from an anterior position. The
extensor muscle is partially reflected along its ventral border to allow the
flexor to be seen. The relative positions of the proximal, mid and distal
regions of the muscles discussed in the text are indicated. (B) More precise
organization of the extensor carpopodite, viewed from an anterior position.
(C) More precise organization of the flexor carpopodite, viewed from a
posterior position. The arrows in B and C indicate the insertion point of the
apodeme, with the insertion of the extensor being superior to the flexor.
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Fig. 3. Muscle fiber length as a function of anatomical position in the extensor
carpopodite of a 27 g crab. (A) Extensor muscle illustrating the position of
the proximal (prox) and distal (dist) fibers (shaded) in relation to the
larger mid-region fibers (unshaded). (B) Relative fiber lengths of fibers from
different regions (shaded bars correspond to shaded regions in A). On average,
the mid-region fibers are significantly longer than the proximal/distal fibers
(*P<0.0001; t-test comparing lengths from the
mid-region fibers with the proximal and distal fibers; N=18;
±s.e.m.). The relative lengths of fibers in the flexor carpopodite
muscles are similar to the pattern shown here.
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Fig. 5. Determination of muscle shortening velocity in vivo. (A) Single
frame of a crab running on the treadmill. Second walking legs were marked with
red paint at the distal portion of the meropodite and at the distal end of the
propopodite. These points were subsequently used to follow angular changes in
the meropodite–carpopodite joint during rapid running. (B) Dissected
legs were used to measure changes in muscle length (arrows along apodeme)
associated with measured changes in joint angle. (C) Joint angle as a function
of time is used to determine angular velocity during running.
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Fig. 6. Summary of alternate myofibrillar protein isoforms identified in the
extensor and flexor carpopodite muscles. (A) Three isoforms of myosin heavy
chain (MHC) are expressed and numbered in the order from least to greatest
migration on SDS-PAGE gels (silver stain). The sample on the left is from a
single fiber from the mid-region of the muscle and co-expressed both
MHC1 and MHC3. The sample on the right is from a single
proximal/distal fiber and expressed only MHC2. (B) Three isoforms
of troponin T (TnT) are expressed (western blot). The sample on the left is
from a fiber from the mid-region of the muscle and expressed only
TnT3. The sample on the right is from a proximal/distal fiber and
expressed both TnT1 and TnT2. (C) Two isoforms of
troponin I (TnI) are expressed in various ratios (western blot). Shown is a
single fiber sample that expressed both (TnI1 and TnI2)
isoforms.
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Fig. 7. Myosin heavy chain (MHC) isoform expression as a function of anatomical
location in extensor carpopodite muscles. Proximal and distal fibers
frequently express MHC2 but the proportion is variable and is
correlated with animal size. In general, MHC2 is more prevalent in
larger sized crabs. Here, fibers from a medium sized crab (18.7 g) exhibits
MHC2 expression in some fibers of the proximal region but not in
the distal fibers. By contrast, the muscle from the large (55 g) crab exhibits
MHC2 expression in all of the fibers from the proximal and distal
muscle regions. In some of these fibers, MHC2 is present in
combination with MHC1 and MHC3. The arrows associated
with the mid-region fibers indicate that the samples represent a continuum in
anatomical location, with the samples closer to the proximal and distal
samples being taken from adjacent to these locations within the muscle.
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Fig. 8. Sequence comparison of three myosin heavy chain (MHC) cDNAs isolated from
muscles of the crab meropodite. Nucleotides that match among all three
sequences are shaded in black and the stop codon (TAA) for each sequence is in
bold text and underlined. Within the open reading frame, the sequences share
approximately 80% sequence identity but show significant divergence in the
3'-UTR.
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Fig. 9. Troponin T (TnT) isoform expression as a function of anatomical location in
flexor carpopodite muscles of a smaller (A) and larger (B) crab. Mid-region
(mid) fibers express the TnT3 isoform whereas the more proximal
fibers express either TnT2 or a combination of TnT1 and
TnT2. In general, TnT1 expression is more prevalent in
larger crabs. In this example, the proximal (prox) fibers from the 6 g crab
express the TnT2 isoform almost exclusively (A) whereas the fibers
of the 70 g crab contain significant levels of TnT1 (B). Each of
the three replicates from different crabs or muscle regions are single fibers
from the indicated muscle region.
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Fig. 10. Troponin I (TnI) isoform expression as a function of anatomical location in
flexor carpopodite muscles of a smaller (A) and larger (B) crab. In the 18.7 g
crab flexor, the mid-region (mid) fibers express primarily the TnI1
isoforms, with little or no TnI2 being present (A). By contrast,
the proximal (prox) fibers from the same muscle possess nearly equal amounts
of both isoforms (A). In the muscles from the 63 g crab, both TnI isoforms are
co-expressed in approximately equal proportions in fibers from both the mid-
and proximal regions. The three samples from different crabs or muscle regions
are replicates of single fibers from the indicated muscle region.
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Fig. 11. Expression of 75 kDa protein in fibers from different anatomical regions of
flexor carpopodite muscle of a 63 g crab. Expression of this protein is
observed in each fiber type in approximately equal amounts. P75 in other
decapod crustaceans is expressed exclusively in fast fiber types. Mid,
mid-region fibers; prox, proximal fibers; dist, distal fibers.
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© The Company of Biologists Ltd 2009
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µm) as compared with the mid-region fibers. What initially appears to be
the outer muscle cell membrane delineating a single fiber is actually an
in-folding of the membranes resulting in a functional subdivision of the
fibers (arrows). (C) Cross section of fibers from the mid-region of the muscle
(scale as in B). These fibers are significantly larger in diameter (
).