Download Regulation of Muscle Growth and Sarcomeric Protein Gene

AMER. ZOOL., 39:570-579 (1999)
Regulation of Muscle Growth and Sarcomeric Protein Gene Expression
over the Intermolt Cycle1
ALICIA J. E L HAJ 2
School of Postgraduate Medicine, Keele University, Hartshill, Stoke on Trent ST4 7QB, UK
Tel: (0)1792 554605, Fax: (0)1782 747319
SYNOPSIS. Crustacean muscle growth is associated with a hormonally mediated
cyclical molt stage. The mechanisms by which fibre lengthening and hypertrophy
occur in Crustaceans over the molt has been the subject of our and other researchers' investigations using histological, biochemical and molecular approaches. In
this paper, we review our studies and present evidence for the different molecular
mechanisms by which sarcomeric proteins are upregulated to achieve muscle sarcomere addition in lobsters during the molt.
Synthesis of the sarcomeric proteins has been shown to increase during the premolt and postmolt phases in the leg and abdominal muscles coinciding with the
addition of sarcomeres over ecdysis. This is in contrast to research on claw muscle
demonstrating premolt atrophy. Our work and others' have investigated the factors which modulate this growth and turnover of muscle tissue in crustaceans.
These changes in muscle turnover correspond with an elevated titre of circulating
ecdysteroids and the role of these molting hormones in regulating sarcomeric
mRNA and protein levels during cyclical muscle growth is discussed.
Our results suggest that sarcomeric proteins may be controlled via both transcriptional and translational mechanisms during the molt interval and these findings are discussed in relation to previous research investigating muscle growth in
Crustacea.
INTRODUCTION
Pioneering work by Dorothy Skinner and
colleagues first began to consider changes
in muscle mass through the molt cycle in
the claws of the land crab, Gecarcinus lateralis, in the mid 60s (Skinner, 1965,
1966). Our work has contributed to this
field with an emphasis on the growth of leg
and abdominal muscles in a variety of different crustacean species. It has involved
histological and biochemical analysis of
muscle fibre lengthening and hypertrophy
in predominantly decapod crustaceans.
These studies have been extended to include investigations at the molecular level
into muscle sarcomeric protein gene regulation. This review will cover these investigations and draw together some general
1
From the Symposium The Compleat Crustacean
Biologist: A Symposium Recognizing the Achievements
of Dorothy M. Skinner presented at the Annual Meeting of the Society for Integrative and Comparative Biology. 3-7 January 1998, at Boston. Massachusetts.
2
E-mail: [email protected]
conclusions regarding muscle growth and
the factors which regulate this growth.
Histological studies identify the stages of
muscle growth in the leg and the abdomen
Fibre length and sarcomere number in
the extensor muscle of the walking leg has
been quantified in a number of decapod
crustaceans over the intermolt cycle (El Haj
et al., 1984; Houlihan and El Haj, 1985).
These studies have demonstrated that muscle growth occurs by addition of new sarcomeres at ecdysis in Carcinus maenas and
Homarus americanus. Autoradiographic localisation of labelled sarcomeric proteins
has shown that sarcomeres may be added at
the end of the fibres at the site of the attachment with the exoskeleton. This raises
interesting questions regarding the ability of
the muscle to function during ecdysis.
When the new exoskeleton is being laid
down, muscle fibres are increasing in length
and reattaching. Our attempts to identify assembling sarcomeres during this period using electron microscopy have been successful in identifying shorter sarcomeres at the
570
REGULATION OF MUSCLE GROWTH
ends of fibres which in some cases lack the
filament organisation (Fig. la, b). However,
it is not possible to confirm that these fibres
are indeed not artefacts of fixation as a result of a softer cuticle. The situation is further complicated by early observations in
the 60/70s of the presence of supercontracted sarcomeres in invertebrates and vertebrates by Hoyle et al. (1965), and Rice
(1973). Supercontraction may be occurring
in these growth regions where the muscle
is forming the new attachment to the cuticle. What our evidence does confirm is that
fibres are lengthening during the pre and
postecdysial period by the addition of sarcomeres, but the process of assembly has
yet to be characterized. Muscle hypertrophy
may be occurring as a result of regulatory
processes different from to those occurring
during fibre lengthening. Morphometric
analysis of myofibrillar surface area in leg
muscles of C. maenas has demonstrated increases that result from the addition of thick
and thin filaments. Analysis of size classes
of myofibrils has suggested that growth of
the myofibrils may be occurring by longitudinal myofibrillar splitting as in vertebrate
muscle (El Haj et al., 1984). Our results
have suggested that in contrast to growth
occurring in length during a restricted phase
of the molt cycle, muscle may be growing
in bulk throughout the molt cycle by the
addition of thick and thin filaments. This
would account for the anecdotal observations that the muscle does not appear to fill
the space in the lobster or crab immediately
after the molt when the animal has expanded in size. This observation leads us to consider if the process of hypertrophy and
lengthening are regulated differentially and
how these processes are occurring.
571
peaks during the premolt and early postmolt
(El Haj and Houlihan, 1987; El Haj et al.,
1996; Mykles and Skinner, 1985). Using
this technique on animals in the premolt
phase, protein synthesis rates in vivo have
been shown to increase in all three muscle
groups, leg, abdominal and claw muscle of
the American lobster, Homarus americanus
(El Haj et al. 1995) (Fig. 2a). These findings have also been observed in the green
shore crab in vitro, Carcinus maenas, and
the crayfish, Austropotamobius pallipes
(Whiteley et al, 1993; Whiteley et al.,
1996). Early in vitro work by Skinner
(1965) showed elevated amino acid incorporation in muscles and other tissues in the
land crab in the premolt land crab, G. lateralis. El Haj et al., 1995, have suggested
that the premolt elevation of protein synthesis occurs prior to the assembly of the
sarcomeres during the early postmolt period
and accounts for the synthesis of predominantly sarcomeric and other associated
muscle proteins. In addition, Mykles (1997)
proposes that the increase in synthesis at
premolt reflects increased turnover of myofibullar proteins, which facilitates the rearrangements of myofilaments observed.
Using cDNA probes to 18S ribosomal
RNA for assessing ribosomal quantity, we
have also shown that elevations in the rate
of protein synthesis is not accompanied by
an elevation in total ribosomal RNA in claw
muscle in the American lobster (El Haj et
al., 1995). In some other species, increasing
ribosomal number is a mechanism for overall increased protein processing at key stages of development. However, in the lobster,
increases in protein synthesis is not due to
enhanced ribosomal numbers but appears to
be due to enhanced ribosomal activity and
increased transcription and mRNA producMuscle protein turnover during the molt
tion in the muscle.
cycle
The premolt elevation in protein syntheThese histological observations coincide sis is not necessarily linked to an overall
with biochemical experiments using la- elevation in muscle mass in all the muscle
belled amino acid precursors in vivo and in groups in the animal. Evidence for this
vitro. By adapting flooding dose techniques comes from studies by Skinner, Mykles and
originated for mammalian turnover studies colleagues on the claw muscle. At the stage
(Garlick et al., 1980), we have been able to when protein synthesis is elevated, extensor
measure muscle protein turnover in vivo. and flexor muscles in the claw are underThese studies demonstrate that total muscle going up to 60% muscle atrophy (Skinner,
protein synthesis rates are elevated with 1965; Mykles and Skinner, 1982). Corre-
572
ALICIA J. E L HAJ
573
REGULATION OF MUSCLE GROWTH
1.2
0.8
• Leg
1.0
0 Abdomen
GDClaw
~ 0.6
'>. 0.8
-3
c
I 0.6
£ 0.4
a.
~
04
0.2
0.2
0
i
C
C
I 1
£ c.
=0
Postmoult
Intermoult
Injected
Premoult
a)
Control
b)
FIG. 2. a) A] Rate of protein synthesis per day (K,) in three muscle groups (leg, abdomen and claw) in the
lobster Homarus americanus at three stages of the moult cycle (n = 4) B] Amount of protein synthesised per
day as a proportion of the total pool of RNA (KRNA) or a measure of ribosomal activity) in three muscle groups
(leg, abdomen and claw) at three stages of the moult cycle. Values represent means + SEM. An asterisk indicates
a significant difference from the value for the intermolt stages (P < 0.05). b) A] Rate of protein synthesis per
day (K,) 3 days following an injection of a premolt concentration of 20-hydroxyecdysone (20-HE) (10~6 mol 1"')
into three muscle groups in the lobster H. americanus. Controls were injected with saline (n = 6). B] Ribosomal
activity in three muscle groups in the lobster 3 days after injection of 20-HE. Values represent means + SEM.
An asterisk indicates a significant difference from the value for the control group (P < 0.01).
sponding rates of protein degradation are
also elevated in the claw tissue during the
premolt. The resultant loss in muscle mass
enables the claw to be drawn through the
narrow basi-ischium joint (Mykles and
Skinner, 1990). Whether the claw muscle is
being differentially regulated compared to
other muscle groups in the crab has not
been determined. Mykles and Skinner
(1982, 1990) proposed that there is an increase in the synthesis of Ca2+ dependant
proteinases for the specific regulation of
FIG. I. Longitudinal section of sarcomeres from the immediate postmolt muscle fibre in Homarus americanus.
35,000 X magnification, a) Electron micrograph showing the structure of the sarcomeres in the exoskeletal
region in Homarus americanus. Note the greater proportion of thin filaments to thick filaments and the lack of
organisation of the filaments into clear bands. Sarcoplasmic reticulum and mitochondria are present, although T
tubule and dyad formation is not evident, b) Electron micrograph of the middle region of the fibre showing the
sarcomeres with "normal" banding and typical arrangement of thick and thin filaments observed in striated
muscle. Sarcomere length = 5 u.m.
574
ALICIA J. EL HAJ
myofibrillar proteins during atrophy. One peak during premolt continuing through to
theory is that these proteinases may be re- a lesser extent during postmolt in a number
sponding to an increase in calcium titre in of different crustacean species (Chang,
the haemolymph during the premolt.
1993). The elevations in protein synthesis
Further evidence for differential muscle in Homarus americanus (El Haj et al.,
protein synthesis has been found when con- 1995) correspond to the stages during
sidering the growth of the muscle in the iso- which previous measurements have shown
pod, a crustacean which develops a biphasic an elevation in ecdysteroid titre, i.e., during
molt. In these animals, the molt is biphasic the Dl-3 stage (Snyder and Chang, 1991).
with subsequent differential growth of the Research using radiolabelled hormone
two portions of the animals, the posterior binding assays has detected the presence of
portion molting first followed by the ante- ecdysteroid receptors in a number of tissues
rior portion (Steel, 1982). Our work on the in Carcinus maenas and Artemia sp. (El
isopod has studied growth of the muscle
over the biphasic molt in an attempt to un- Haj et al., 1997). In these studies the titre
ravel the regulation and timing of ecdysial of ecdysteroid within the muscles has been
muscle growth. Increases in size occur in shown to be low compared to other tissues
two phases separated by hours or days ac- within crustaceans. This has hampered
cording to the species which suggested that progress in determining the role of this horthe muscles may grow biphasically. Using mone in controlling muscle growth. Howradiolabelled phenylalanine in vivo flooding ever, ecdysteroids have been shown to have
techniques, we have measured rates of pro- a direct effect on muscle turnover. Whiteley
tein synthesis in the muscle and showed et al. (1991), demonstrated how doses of
that they were elevated in the anterior and ecdysteroid administered in vitro to isolated
the posterior portion during the premolt leg muscles in culture could have an effect
compared to the intermoult rates (Whiteley on RNA synthesis rates in a dose responand El Haj, 1997). In contrast, protein syn- sive manner. Furthermore, studies have
thesis rates in the ventral longitudinal mus- shown that 20 hydroxyecdysone injected in
cle, which lies along the length of the body, vivo result in elevated protein synthesis in
were elevated by 3 fold in the anterior half the claw, leg and abdominal muscle of the
of the muscle as compared to the posterior lobster after three days (El Haj et al., 1995)
half during half molt when the posterior (Fig. 2b). Ecdysteroids have been shown to
exoskeleton has shed (Whiteley and El Haj, have direct effects on protein synthesis rates
1997). This difference was also measured in other crustacean tissues, such as exountil 36 hours postmolt when levels are skeleton, hypodermis and hepatopancreas
equilibrated to intermolt. Interestingly, actin (Stringfellow and Skinner 1988; Traub et
and myosin mRNA remained constant between biphasic molts which agrees with our al., 1987; Paulson and Skinner, 1991).
findings in the lobster. Systemic levels of These results suggest that ecdysteroids are
ecdysteroid were equilibrated in the anterior playing a key role in elevating protein synand posterior portions of the isopod. This thesis in preparation for the molt.
More recently, ecdysteroid receptors
implies that differential growth could be
have
been localized in the premolt muscle
regulated as a function of changing receptor
expression. This regulation may interact at of lobsters using a heterologous Drosophila
the level of translation of proteins and sar- antibody for immunocytochemical and
comeric assembly. These studies on growth Western blot techniques (El Haj et al.,
patterns of differing muscle groups through 1994; Koelle et al., 1991). Western blots
the molt raise interesting questions regard- using the EcR antibody, hybridised with a
ing how muscles may be differentially reg- 95—110 kDa protein from the lobster tissues
ulated in crustaceans.
examined. Sections of the eyestalk neural
tissue showed cytoplasmic localisation of
Ecdysteroids: Their role in regulation of
the EcR in the neural cells associated with
muscle growth
the X-organ/sinus gland complex. MolecuEcdysteroids, the major molt regulating lar approaches have included cloning the
hormones in Crustacea, have been shown to crustacean receptor for ecdysteroid from
REGULATION OF MUSCLE GROWTH
Uca pugilator (Durica and Hopkins, 1996)
and an ecdysteroid responsive DNA binding protein from the lobster Homarus americanus (El Haj et al., 1997). The Homarid
ecdysteroid responsive gene, HHR3, has a
ligand binding region which contains conserved sites with the steroid receptor superfamily. In response to in vivo injection into
intermolt animals of 20 hydroxyecdysone,
HHR3 mRNA levels are elevated in the epidermis and leg muscle after 6 hr (Fig. 3).
In contrast, the sinus gland/x organ shows
an opposing pattern of expression. HHR3
expression varies in tissues from these animals at the premolt and postmolt stages
which co-ordinate with other key modulations (Fig. 4). Evidence is mounting to support the theory that these ecdysteroids are
acting at the level of transcription possibly
through a cascade of DNA binding factors
to increase sarcomeric protein synthesis
during the premolt period. Further recent
evidence for a cascade of ecdysteroid responsive transcription factors includes the
identification of a shrimp E75 homologue,
an early ecdysteroid responsive DNA binding protein, which may be involved in
downstream regulation of key target proteins during development or the moult cycle
in crustaceans (Chan, 1998).
Regulation of sarcomeric protein genes in
Crustacea
Relatively few crustacean sarcomeric
protein genes have been cloned and made
available for use in molecular studies of
crustacean growth. The majority have been
cloned in the brine shrimp, Artemia sp. (El
Haj, 1996). Therefore in order further to investigate the molecular basis for the control
of muscle growth and development in lobsters, we along with other groups have first
had to clone specific cDNAs which could
be used to investigate regulatory mechanisms. Using heterologous primers and
PCR, we have cloned a 736 bp fragment
including the majority of the coding region
of the H. gammarus sarcomeric protein, actin (Harrison and El Haj, 1994) and recognises a 1.6 kb mRNA in fast and slow
fibres. In addition, cDNA probes for Homarus sp. fast and slow heavy chain myosin
and tropomyosins have been cloned by the
575
group of Mykles and colleagues (Cotton
and Mykles, 1994; Mykles et al, 1998).
The fast myosin heavy chain clone contains
the C terminus and 3' untranslated region
which enables specificity for the fast isoform of MHC. We have begun to clone myosin heavy chain isoforms from various
species including the Antarctic isopod,
Glyptonotus antarcticus. These studies currently underway are focusing on identifying
the presence of temperature related myosin
isoforms in crustaceans from differing habitats and subjected to varying rearing temperatures.
Little information is available on the promoter or regulatory regions present in crustacean genes. Few genomic clones have
been isolated with little corresponding genomic analysis. In Artemia, analysis of the
5' end of the SERCA gene has revealed a
number of common regulatory and promoter sequences including those involved
in the MyoD family and MEF-2 binding
sites (Escalante and Sastre, 1994). These
regulatory sequences, such as MyoD and
MEF 2, are involved in controlling differentiation of muscle cells. Further work is
needed to identify how crustacean sarcomeric protein genes are being regulated
over the molt cycle and to identify some of
the key promoters responsible for their regulation.
Our research has concerned the effect of
regulating factors on sarcomeric protein
mRNA expression such as mechanical forces, temperature and hormone levels. Work
by Harrison and El Haj (1994) has demonstrated that lobster muscle is stretch responsive and that the actin mRNA up-regulation is triggered by stretch and sarcomere elongation. In this case the immobilised limbs reacted slowly and mRNA
levels took up to 2 weeks to rise. This
would potentially be too slow to play a
functional role for a stimulus as a result of
cuticle stretching over the molt (although
the amount of stretch imposed may not be
directly comparable). However, as has been
shown for mammalian muscle (Goldspink
et al., 1994), crustacean muscle fibres are
stretch responsive resulting in mRNA upregulation and elevated synthesis.
Varied results in different species have
576
ALICIA J. EL HAJ
IN VIVO 20-HE INJECTION
HOMARUS AMERICANUS
0
6
21 48
HRS POST INJECTION
A)
Epidermis
18S
B)
Leg muscle
18S
0
Sinus gland / x organ
18 S
FIG. 3. Northern blot analysis of (A) epidermal, (B) leg muscle and (C) sinus gland/x-organ complex, from the
eyestalk of H. americanus after injection of 20E. RNA samples were extracted from these tissues at 0, 6, 21 and
48 hr post-injection. Relative loading of the lanes was determined using a probe for 18S RNA. Leg muscle tissue
was composed of extensor and flexor muscles that were dissected free of surrounding epidermal tissue.
577
REGULATION OF MUSCLE GROWTH
Leg muscle
7
18 26
32
41
50
70 78
90 104 134 135
70
90
X organ /sinus gland
7
18
26
32
11
50
78
104 134 135
Days postmoult
Epidermis
T
0-15
0-1 _
T
005 -
Post
Inter
Pre
FIG. 4. Levels of HHR3 raRNA over the molt cycle
in H. americanus in leg muscle, x-organ/sinus gland,
and epidermis. Graphs represent densitometric analyses of HHR3 levels as ratios to 18S RNA. Days through
the molt cycle are indicated on the x-axis and correspond to the stages (post, inter and pre) listed on the
lower x-axis.
been obtained regarding elevated mRNA
levels throughout the molt for actin and myosin (El Haj and Whiteley, 1997; Whiteley
and El Haj, 1997; Varadaraj et al., 1996).
This may be partially due to the large interindividual variation in wild and laboratory
reared species of Crustaceans. In muscles of
Gecarcinus and Carcinus sp., actin mRNA
levels are elevated during the pre and postmoult periods in comparison to intermolt
levels (Whiteley et al., 1991; Varadaraj et
al., 1996) In juvenile lobster, although there
is a great deal of inter-individual variation,
the overall trend in the levels of actin remain constant throughout the moult cycle
in claw and other muscle tissues (Whiteley
and El Haj, 1997). Mykles (1997) demonstrated that mRNA level of myosin HC decreases over the premolt period in the land
crab even though synthesis of the protein
increases about ninefold. It appears that
both transcriptional and translational processes may be involved in modulation of
growth of crustacean muscle; a similar finding to research on mammalian muscle
(Endo and Nadal Ginard, 1987). Mammalian studies have shown that there are significant differences observed in muscle in
translational efficiency, thus transcript accumulation is unlikely to be the only determinant of sarcomeric assembly (Endo and
Nadal Ginard, 1987). Results from our investigations, as well as Mykles 1997, show
that actin and myosin mRNA may not show
co-ordinate regulation through the molt in
abdominal muscle. Mykles (1997) has
shown that myosin mRNA levels in the
claw decline during premolt in G. lateralis
when other sarcomeric proteins are elevating in expression. This is in contrast to
studies of myogenesis in mammals and humans where total mRNA is maintained with
similar stoichiometry in the different stages
of muscle development (Wade et al., 1990).
Finally, there is little information to address if there are developmental isoforms of
sarcomeric proteins which may be expressed during molt induced muscle
growth. Drosophila have 6 actin genes that
are developmentally expressed in varying
isoforms (Fyrberg et al., 1983). Varadaraj
et al. (1996) have indicated 7-11 actin
genes using Southern blot analysis of the
G. lateralis genome. Only two or three partial actin sequences have been cloned and a
full analysis of expression patterns with development and the molt has yet to be carried out. It is possible that actin isoforms
may be varying in expression through the
molt, but these differences are not being
identified using the cDNAs available. What
is clear is that crustaceans represent an excellent model for studies on muscle growth
and plasticity and molecular approaches can
now be applied to these models to further
understand these processes.
REFERENCES
Chan, S. M. 1998. Cloning of a cDNA encoding a
putative molt-inhibiting hormone from the eyestalk of the sand shrimp, Melapenatus ensis. Febs.
Lett. 395-400.
578
ALICIA J. E L HAJ
Chang, E. S. 1993. Comparative endocrinology of
molting and reproduction: Insects and crustaceans.
Annu. Rev. Entomol. 38:161-180.
Cotton, J. L. S. and D. L. Mykles. 1994. Cloning of a
crustacean myosin heavy chain isoform—exclusive expression in fast muscle. J. Exp. Zool. 267:
578-586.
Durica, D. S. and P. M. Hopkins. 1996. Expression of
the genes encoding the ecdysteroid and retinoid
receptors in regenerating limb tissue from the fiddler crab, Uca pugilator. Gene 171(2):237-241.
El Haj, A. J. 1996. Crustacean genes involved in
growth. In S. Ennion and G. Goldspink (eds.),
Vol. 48, Gene regulation in aquatic organisms,
pp. 94-1 12 SEB Seminar Series CUP, Cambridge.
El Haj, A. J., S. R. Clarke, P. Harrison, and E. S.
Chang. 1995. In vivo muscle protein synthesis
rates in the American lobster, Homarus americanus, during the molt cycle and in response to 20
Hydroxyecdysone. J. Exp. Biol. 199:1-5.
El Haj, A. J., C. K. Govind, and D. E Houlihan. 1984.
Growth of the lobster leg muscle fibres over intermolt and molt. J. of Crust. Biol. 4(4):536-545.
El Haj, A. J., S. L. Tamone, M. Peake, P. Sreenivasula
Reddy, and E. S. Chang. 1997. An ecdysteroid
responsive gene in a lobster—a potential crustacean member of the steroid hormone receptor superfamily. Gene 201:127-135.
El Haj, A. J., P. Harrison, and E. S. Chang. 1994. Localisation of ecdysteroid receptor immunoreactivity in eyestalk and muscle tissue of the American
lobster, Homarus americanus. J. Exp. Zool. 270:
343-349.
El Haj, A. J. and D. F. Houlihan. 1987. In vitro and in
vivo protein synthetic rates in a crustacean muscle
during the molt cycle. J. Exp. Biol. 127:413-427.
El Haj, A. J. and N. M. Whiteley. 1997. Molecular
regulation of muscle growth in crustacean J. Mar.
Biol. Assoc. 77:95-106.
Escalente, R. and L. Sastre. 1994. Structure of Artemia
franciscana sarco/endoplasmic reticulum Ca
ATPase. J. Biol. Chem. 269:13005-13012.
Endo, T. and B. Nadal Ginard. 1987. Three types of
muscle specific gene expression in fusion blocked
rat skeletal muscle cells. Translational control in
EGTA treated cells. Cell 49:515-526.
Fyrberg, E. A., J. W. Mahaffey, B. J. Bond, and N.
Davidson. 1983. Transcripts of 6 Drosophila actin
genes accumulate in a stage and tissue specific
manner. Cell 33:115-123.
Garlick, P. J., M. A. McNurlan, and V. R. Preedy.
1980. A rapid and convenient technique for measuring the rate of protein synthesis in tissues by
injection of 3H phenylalanine. Biochem. J. 192:
719-723.
Goldspink, G., G. E Gerlach, T. Jaenicke, and P. Butterworth. 1994. Stretch, overload and gene expression in muscle. In E Lyall and A. J. El Haj
(eds.), Cells and biomechanics, pp. 81-96. SEB
Sem Ser 54, Cambridge Univ. Press.
Harrison, P. and A. J. El Haj. 1994. Actin mRNA levels and myofibrillar growth in leg muscles of the
European lobster in response to passive stretch.
Mol. Mar. Biol. and Biotech. 3:35-42.
Houlihan, D. E and A. J. El Haj. 1985. An analysis of
the growth of a crustacean muscle. In A. Wenner
(ed.), Factors in adult growth, Crustacean issues,
Vol. II, pp. 15-29. Proceedings of the Society of
American Zoologists. Balkema Press.
Hoyle, G., J. H. McLear, and A. Selveston. 1965.
Mechanism of supercontraction in a striated muscle. J. Cell Biol. 26:621-640.
Koelle, M. R., W. S. Talbot, W. A. Segraves, M. T.
Bender, P. Cherbas, and D. Hogness. 1991. The
Drosophila ECR gene encodes an ecdysone receptor, a new member of the steroid receptor family.
Cell 67:59-77.
Mykles, D. L. 1997. Crustacean muscle plasticity: Molecular mechanisms determining mass and contractile properties. Comp. Biochem. Physiol.
117B:367-378.
Mykles, D. L , J. L. S. Cotton, H. Tamaguchi, K.-I.
Sano, and Y. Maeda. 1998. Cloning of tropomyosins from lobster (H. americanus) striated muscles: Fast and slow isoforms may be generated
from the same transcript. J. Muscle Res. and Cell
Motility 19:2105-115.
Mykles, D. L and D. M. Skinner. 1982. Crustacean
muscle: Atrophy and regeneration during molting.
In B. M. Twarog, R. J. C. Levine, and M. M.
Dewey (eds.), Basic biology of muscles; A comparative approach, pp. 337-357. Raven Press,
New York.
Mykles, D. L. and D. M. Skinner. 1985. Muscle atrophy and restoration during molting. In A. Wenner
(ed.), Crustacean growth, pp. 31-46. A A Balkema, Rotterdam.
Mykles, D. M. and D. M. Skinner. 1990. Atrophy of
crustacean somatic muscle and proteinases that do
the job. A Review. J. Crustacean Biology 10:577594.
Paulson, C. R. and D. M. Skinner. 1991. Effects of 20hydroxyecdysone on protein synthesis in tissue of
the land crab, Gecarcinus lateralis. J. Exp. Zool.
257:70-79.
Rice, M. J. 1973. Supercontracting striated muscle in
a vertebrate. Nature 243:238-240.
Skinner, D. M. 1965. Amino acid incorporation into
protein during the molt cycle of the land crab,
Gecarcinus lateralis. J. Exp. Zool. 16:226—233.
Skinner, D. M. 1966. Breakdown and reformation of
somatic muscle during the molt cycle of the land
crab, Gecarcinus lateralis J. Exp. Zool. 163:115—
124.
Snyder, M. J. and E. S. Chang. 1991. Ecdysteroids in
relation to the molt cycle of the American lobster,
Homarus americanus. I. Hemolymph titers and
metabolites. Gen. Comp. Endocrinol. 81:133—145.
Steel, C. G. H. 1982. Stages of the intermolt cycle in
the terrestrial isopod, Oniscus asellus and their relation to biphasic cuticle secretion. Can J. Zool.
60:429-437.
Stringfellow, L. A. and D. M. Skinner. 1988. Molt cycle correlation patterns of synthesis of integumentary problems in the land crab, Gecarcinus lateralis Dev. Biol. 128(1):97-110.
Varadaraj, K.. S. S. Kumari, and D. M. Skinner. 1996.
Actin encoding cDNAs and gene expression dur-
REGULATION OF MUSCLE GROWTH
ing the intermolt cycle of the Bermuda land crab,
Gecarcinus lateralis. Gene 171(2): 177—84.
Wade. R., C. Sutherland, R. Gahlmann, L. Kedes, E.
Hardeman, and P. Gunning. 1990. Regulation of
contractile protein gene family mRNA pool sizes
during myogenesis. Dev. Biol. 142:270-282.
Whiteley, N. M. and A. J. El Haj. 1997. Regulation of
muscle gene expression over the molt cycle.
Comp. Biochem. Physiol. 117B(2):30-32.
Whiteley, N. M. and E. W. Taylor. 1993. The effects
of seasonal variation in temperature on extracellular and acid base status in a wild population of
the crayfish Austropotamobius pallipes. J. Exp.
Biol. 181:295-311.
Whiteley, N. M., E. W. Taylor, A. Clarke, and A. J. El
Haj. 1997. Haemolymph oxygen transport and
acid base status in a stenothermal Antarctic crus-
579
tacean, Glyptonotus antarclicus. Polar Biol. (In
press)
Whiteley, N. M. E. W. Taylor, S. C. R. de Souza, and
A. J. El Haj. 1993. Seasonal and molt related
changes in haemolymph oxygen and acid base
levels in a wild population of crayfish of Austropotamobius pallipes. Freshwater Crayfish 9:189—
199.
Whiteley, N. M., E. W. Taylor, and A. J. El Haj. 1991.
Actin gene expression during muscle growth in
Carcinus maenas. J. Exp. Biol. 167:277-284.
Whiteley, N. M., E. W. Taylor, and A. J. El Haj. 1996.
The relationship between rates of metabolism and
protein synthesis in a stenothermal versus a eurythermal isopod crustacean. Am. J. Physiol.
40(5):R1295-1303.
Corresponding Editor: Louis E. Burnett, Jr.