Analysis of myofibrillar proteins and transcripts in adult skeletal muscles of the American lobster Homarus americanus: variable expression of myosins, actin and troponins in fast, slow-twitch and slow-tonic fibres

Differentiation and Maturation of Muscle and Fat Cells in Cultivated Seafood: Lessons from Developmental Biology

Cultivated meat, also known as cultured or cell-based meat, is meat produced directly from cultured animal cells rather than from a whole animal. Cultivated meat and seafood have been proposed as a means of mitigating the substantial harms associated with current production methods, including damage to the environment, antibiotic resistance, food security challenges, poor animal welfare, and-in the case of seafood-overfishing and ecological damage associated with fishing and aquaculture. Because biomedical tissue engineering research, from which cultivated meat draws a great deal of inspiration, has thus far been conducted almost exclusively in mammals, cultivated seafood suffers from a lack of established protocols for producing complex tissues in vitro. At the same time, fish such as the zebrafish Danio rerio have been widely used as model organisms in developmental biology. Therefore, many of the mechanisms and signaling pathways involved in the formation of muscle, fat, and other relevant tissue are relatively well understood for this species. The same processes are understood to a lesser degree in aquatic invertebrates. This review discusses the differentiation and maturation of meat-relevant cell types in aquatic species and makes recommendations for future research aimed at recapitulating these processes to produce cultivated fish and shellfish.

Identification of allergens for food-dependent exercise-induced anaphylaxis to shrimp

Shrimp is a causative food that elicits food-dependent exercise-induced anaphylaxis (FDEIA). In this study, we sought to identify IgE-binding allergens in patients with shrimp-FDEIA. Sera were obtained from eight patients with shrimp-FDEIA and two healthy control subjects. Proteins were extracted from four shrimp species by homogenization in Tris buffer. Immunoblot analysis revealed that IgE from patient sera bound strongly to a 70-kDa and a 43-kDa protein in a preparation of Tris-soluble extracts from Litopenaeus vannamei. Mass spectrometry identified the 70-kDa and 43-kDa proteins as a P75 homologue and fructose 1,6-bisphosphate aldolase (FBPA), respectively. To confirm that the putative shrimp allergens were specifically recognized by serum IgE from shrimp-FDEIA patients, the two proteins were purified by ammonium sulfate precipitation followed by reversed-phase HPLC and/or anion-exchange hydrophobic interaction chromatography and then subjected to immunoblot analysis. Purified P75 homologue and FBPA were positively bound by serum IgE from one and three, respectively, of the eight patients with shrimp-FDEIA, but not by sera from control subjects. Thus, P75 homologue and FBPA are identified as IgE-binding allergens for shrimp-FDEIA. These findings could be useful for the development of diagnostic tools and desensitization therapy for shrimp-FDEIA patients.

Mixing it up: the biological significance of hybrid skeletal muscle fibers

Skeletal muscle fibers are classified according to the myosin heavy chain (MHC) isoforms and other myofibrillar proteins expressed within these cells. In addition to 'pure' fibers expressing single MHC isoforms, many fibers are 'hybrids' that co-express two or more different isoforms of MHC or other myofibrillar proteins. Although hybrid fibers have been recognized by muscle biologists for more than three decades, uncertainty persists about their prevalence in normal muscles, their role in fiber-type transitions, and what they might tell us about fiber-type regulation at the cellular and molecular levels. This Review summarizes current knowledge on the relative abundance of hybrid fibers in a variety of muscles from different species. Data from more than 150 muscles from 39 species demonstrate that hybrid fibers are common, frequently representing 25% or more of the fibers in normal muscles. Hybrid fibers appear to have two main roles: (1) they function as intermediates during the fiber-type transitions associated with skeletal muscle development, adaptation to exercise and aging; and (2) they provide a functional continuum of fiber phenotypes, as they possess physiological properties that are intermediate to those of pure fiber types. One aspect of hybrid fibers that is not widely recognized is that fiber-type asymmetries - such as dramatic differences in the MHC composition along the length of single fibers - appear to be a common aspect of many fibers. The final section of this Review examines the possible role of differential activities of nuclei in different myonuclear domains in establishing fiber-type asymmetries.

Exposure to As(III) and As(V) changes the Ca²⁺-activation properties of the two major fibre types from the chelae of the freshwater crustacean Cherax destructor

Arsenic is a known carcinogen found in the soil in gold mining regions at concentrations thousands of times greater than gold. Mining releases arsenic into the environment and surrounding water bodies. The main chemical forms of arsenic found in the environment are inorganic arsenite (As(III)) and arsenate (As(V)). Yabbies (Cherax destructor) accumulate arsenic at levels comparable to those in the sediment of their environment but the effect on their physiological function is not known. The effects of arsenic exposure (10 ppm sodium arsenite, AsNaO2 - 5.7 ppm As(III)) and 10 ppm arsenic acid, Na2HAsO4·7H2O - 2.6 ppm As(V)) for 40 days on the contractile function of the two major fibre types from the chelae were determined. After exposure, individual fibres were isolated from the chela, "skinned" (membrane removed) and attached to the force recording apparatus. Contraction was induced in solutions containing increasing [Ca(2+)] until a maximum Ca(2+)-activation was obtained. Submaximal force responses were plotted as a percentage of the maximum Ca(2+)-activated force. As(V) exposure resulted in lower levels of calcium required for activation than As(III) indicating an increased sensitivity to Ca(2+) after long term exposure to arsenate compared to arsenite. Myosin heavy chain and tropomyosin content in individual fibres was also decreased as a result of arsenic exposure. Single fibres exposed to As(V) produced significantly more force than muscle fibres from control animals. Long-term exposure of yabbies to arsenic alters the contractile function of the two major fibre types in the chelae.

Cloning of skeletal myosin heavy chain gene family from adult pleopod muscle and whole larvae of shrimps

The physiological and biological properties of skeletal muscle in crustacea have not been well understood compared with those of vertebrates. The present study focused on myosin, the major protein in skeletal muscle, from shrimps. In our previous study, two full-length genes encoding myosin heavy chain (MHC), a large subunit of the myosin molecule, were cloned from abdominal fast skeletal muscle of kuruma Marsupenaeus japonicus, black tiger Penaeus monodon and Pacific white Penaeus vannamei shrimps, and named as MHCa and MHCb. In this study, we renamed these as MHC1 and MHC2, respectively, due to the presence of various isoforms newly identified. Partial MHC sequences were identified from pleopod muscle of these shrimps. Two MHCs, named MHC3 and MHC4, were identified from pleopod muscle of kuruma shrimp, whereas two MHCs, named MHC4 and MHC5, were cloned from Pacific white shrimp pleopod. MHC3 was cloned only from black tiger shrimp pleopod. Partial MHC sequences from zoea, mysis, and postlarvae of black tiger and Pacific white shrimps were also determined. The phylogenetic tree demonstrated that most MHCs from pleopod muscle and larval MHCs formed clades with MHC1 and MHC2, respectively. These MHCs were considered to be of fast type, since MHC1 and MHC2 are fast-type MHCs according to our previous study. MHC5 obtained from pleopod muscle of Pacific white shrimp in this study was monophyletic with American lobster Homarus americanus S2 slow tonic MHC previously reported, indicating that MHC5 from Pacific white shrimp is of slow type.

Cloning, expression, and localization of two types of fast skeletal myosin heavy chain genes from black tiger and Pacific white shrimps

The physiology and biochemistry of skeletal muscles in shrimps have been poorly understood compared with those from vertebrates. The present study was conducted focusing on myosin, the major protein in skeletal muscle, from adult specimens of black tiger Penaeus monodon and Pacific white Penaeus vannamei shrimps. Two genes encoding myosin heavy chain (MHC), a large subunit of the myosin molecule, were cloned from abdominal fast skeletal muscle and defined as MHCa and MHCb according to our previous study on kuruma shrimp Marsupenaeus japonicus. Random cloning demonstrated that the MHCb gene (MHCb) was expressed more abundantly than MHCa. The full-length cDNA clones of MHCa and MHCb from black tiger shrimp consisted of 5,926 and 5,914 bp, respectively, which encoded 1,914 and 1,909 amino acids, respectively, whereas those from Pacific white shrimp consisted of 5,923 and 5,908 bp, respectively, which encoded 1,913 and 1,909 amino acids, respectively. Both MHCa and MHCb were considered to be fast muscle type due to their strict localization in fast muscle. The amino acid identities between MHCa and MHCb of black tiger shrimp were 77%, 60%, and 73% in the regions of subfragment-1 (S1), subfragment-2 (S2) and light meromyosin (LMM), respectively, with 71% in total, whereas those of Pacific white shrimp were 78%, 60%, and 73% in the regions of S1, S2, and LMM, respectively, with 72% in total. In situ hybridization and northern blot analysis using different regions from abdominal muscle demonstrated different localizations of MHCa and MHCb transcripts in this muscle, suggesting their distinct physiological functions.

The occurrence of two types of fast skeletal myosin heavy chains from abdominal muscle of kuruma shrimp Marsupenaeus japonicus and their different tissue distribution

Shrimps belong to the class Crustacea, which forms a large, diverse group in the invertebrates. However, the physiology and biochemistry of their skeletal muscles have been poorly understood compared with those from vertebrates including mammals and fish. The present study focused on myosin, the major protein in skeletal muscle, from adult specimens of kuruma shrimp Marsupenaeus japonicus. Two types of the gene encoding myosin heavy chain (MHC), a large subunit of the myosin molecule, were cloned from abdominal fast skeletal muscle and defined as MHCa and MHCb. Protein analysis revealed that the MHCa isoform was expressed at a higher level than the MHCb isoform. The full-length cDNA clones of MHCa and MHCb consisted of 5929 bp and 5955 bp, respectively, which encoded 1912 and 1910 amino acids, respectively. Both were classified into fast muscle type by comparison with the partially deduced amino acid sequences of fast-type and slow-type (S(1), slow twitch) MHCs reported previously for the American lobster Homarus americanus. The amino acid identities between MHCa and MHCb of kuruma shrimp were 78%, 60% and 72% in the regions of subfragment-1, subfragment-2 and light meromyosin, respectively, and 71% in total. In situ hybridisation using anti-sense RNA-specific probes, along with northern blot analysis using different tissues from abdominal muscle, revealed the different localisation of MHCa and MHCb transcripts in abdominal fast skeletal muscle, suggesting their distinct physiological functions.

Muscular tissues of the squid Doryteuthis pealeii express identical myosin heavy chain isoforms: an alternative mechanism for tuning contractile speed

The speed of muscle contraction is largely controlled at the sarcomere level by the ATPase activity of the motor protein myosin. Differences in amino acid sequence in catalytically important regions of myosin yield different myosin isoforms with varying ATPase activities and resulting differences in cross-bridge cycling rates and interfilamentary sliding velocities. Modulation of whole-muscle performance by changes in myosin isoform ATPase activity is regarded as a universal mechanism to tune contractile properties, especially in vertebrate muscles. Invertebrates such as squid, however, may exhibit an alternative mechanism to tune contractile properties that is based on differences in muscle ultrastructure, including variable myofilament and sarcomere lengths. To determine definitively whether contractile properties of squid muscles are regulated via different myosin isoforms (i.e. different ATPase activities), the nucleotide and amino acid sequences of the myosin heavy chain from the squid Doryteuthis pealeii were determined from the mantle, arm, tentacle, fin and funnel retractor musculature. We identified three myosin heavy chain isoforms in squid muscular tissues, with differences arising at surface loop 1 and the carboxy terminus. All three isoforms were detected in all five tissues studied. These results suggest that the muscular tissues of D. pealeii express identical myosin isoforms, and it is likely that differences in muscle ultrastructure, not myosin ATPase activity, represent the most important mechanism for tuning contractile speeds.

Interspecific and intragenic differences in codon usage bias among vertebrate myosin heavy-chain genes

Synonymous codon usage bias is a broadly observed phenomenon in bacteria, plants, and invertebrates and may result from selection. However, the role of selective pressures in shaping codon bias is still controversial in vertebrates, particularly for mammals. The myosin heavy-chain (MyHC) gene family comprises multiple isoforms of the major force-producing contractile protein in cardiac and skeletal muscles. Slow and fast genes are tandemly arrayed on separate chromosomes, and have distinct patterns of functionality and expression in muscle. We analyze both full-length MyHC genes (~5400 bp) and a larger collection of partial sequences at the 3' end (~500 bp). The MyHC isoforms are an interesting system in which to study codon usage bias because of their length, expression, and critical importance to organismal mobility. Codon bias and GC content differs among MyHC genes with regards to functional type, isoform, and position within the gene. Codon bias even varies by isoform within a species. We find evidence in favor of both chromosomal influences on nucleotide composition and selection against nonsense errors (SANE) acting on codon usage in MyHC genes. Intragenic variation in codon bias and elongation rate is significant, with a strong trend for increasing codon bias and elongation rate towards the 3' end of the gene, although the trend is dependent upon the degeneracy class of the codons. Therefore, patterns of codon usage in MyHC genes are consistent with models supporting SANE as a major force shaping codon usage.

The continuum of hybrid IIX/IIB fibers in normal mouse muscles: MHC isoform proportions and spatial distribution within single fibers

Although skeletal muscle fiber types are often defined as belonging to discrete categories, many muscles possess fibers with intermediate phenotypes. These hybrid fiber types can be identified by their expression of two or more myosin heavy chain (MHC) isoforms within the same single fiber. In mouse muscles, the most common hybrid fibers are those coexpressing the IIX and IIB MHC isoforms. In the present study, we focused on these IIX/IIB fibers from normal mouse muscles to determine the relative proportions of MHC isoforms at both the protein and mRNA levels and to examine the longitudinal distribution of isoforms within single fibers. We found that IIX/IIB hybrids represent ∼25 and 50% of the fibers in the mouse tibialis anterior and brachioradialis, respectively. The relative proportion of the IIX and IIB isoforms in these fibers spans a continuum, from predominantly IIB-like hybrids to IIX-like hybrids. Quantitative assessment of mRNA levels using real-time PCR from single fibers indicated that IIB expression dominated over IIX expression in most fibers and that a general correlation existed between mRNA isoform levels and MHC protein content. However, the match between mRNA levels and protein content was not precise. Finally, we measured MHC isoform proportions in adjacent fiber segments and discovered that ∼30% of hybrids possessed significant differences in isoform content along their length. In some instances, the muscle fiber type as defined by MHC content changed completely along the length of a fiber. This pattern of asymmetrical MHC isoform content along the length of single fibers suggests that the multiple myonuclei of a muscle fiber may express distinct myofibrillar isoforms in an uncoordinated fashion.

Migration-related changes in gene expression in leg muscle of the Christmas Island red crab Gecarcoidea natalis: seasonal preparation for long-distance walking

During their annual breeding migration the Christmas Island land crab Gecarcoidea natalis sustains locomotion aerobically for up to 12 h per day compared with just 10 min during the dry season when their muscles quickly become anaerobic. A seasonal transition to an endurance-muscle phenotype would thus seem essential for migrating crabs. The current study employed a gene discovery approach comparing two expressed sequence tag (EST) libraries, one each for leg muscle from dry (non-migrating) and wet season (migrating) crabs. The 14 most abundant transcripts differed in their representation between the two libraries. The abundances of transcripts of genes predicted to code for different proteins forming contractile muscle components, including actin, troponin and tropomyosin, were significantly different between seasons and thus between physiological states. The shift in the isoform composition of the contractile elements provided evidence for a switch from slow phasic (S1) to slow tonic (S2) fatigue-resistant muscle fibres. A tropomyosin (tm) transcript aligned with a tm isoform of lobster (tmS2), and semi-quantitative RT-PCR confirmed this isoform to be more abundant in the migrating crab muscle. Two LIM protein coding genes, a paxillin-like transcript (pax) and a muscle LIM protein (mlp), were relatively up-regulated in muscle of wet season crabs. These proteins have a fundamental role in muscle development and reconstruction, and their comparative up-regulation is consistent with a remodelling of leg muscle for migration in the wet season. Such a transition would result in an increased representation of aerobic endurance-type fibres concomitant with the greater aerobic exercise capacity of the migrating red crabs.

Characterisation of myosin heavy chain gene variants in the fast and slow muscle fibres of gammarid amphipods

Recent molecular work has revealed a large diversity of myosin heavy chain (MyHC) gene variants in the abdominal musculature of gammarid amphipods. An unusual truncated MyHC transcript from the loop 1 region (Variant A(3)) was consistently observed in multiple species and populations. The current study aimed to determine whether this MyHC variant is specific to a particular muscle fibre type, as a change in net charge to the loop 1 region of Variant A(3) could be functionally significant. The localisation of different fibre types within the abdominal musculature of several gammarid species revealed that the deep flexor and extensor muscles are fast-twitch muscle fibres. The dorsal superficial muscles were identified as slow fibres and the muscles extrinsic to the pleopods were identified as intermediate fibres. Amplification of loop 1 region mRNA from isolated superficial extensor and deep flexor muscles, and subsequent liquid chromatography and sequence analysis revealed that Variant A(3) was the primary MyHC variant in slow muscles, and the conserved A(1) sequence was the primary variant in fast muscles. The specific role of Variant A(3) in the slow muscles remains to be investigated.

Skeletal muscle fiber types in the ghost crab, Ocypode quadrata: implications for running performance

Ghost crabs possess rapid running capabilities, which make them good candidates for comparing invertebrate exercise physiology with that of more extensively studied vertebrates. While a number of studies have examined various aspects of running physiology and biomechanics in terrestrial crabs, none to date have defined the basic skeletal muscle fiber types that power locomotion. In the current study, we investigated skeletal muscle fiber types comprising the extensor and flexor carpopodite muscles in relation to running performance in the ghost crab. We used kinematic analyses to determine stride frequency and muscle shortening velocity and found that both parameters are similar to those of comparably sized mammals but slower than those observed in running lizards. Using several complementary methods, we found that the muscles are divided into two primary fiber types: those of the proximal and distal regions possess long sarcomeres (6.2+/-2.3 microm) observed in crustacean slow fibers and have characteristics of aerobic fibers whereas those of the muscle mid-region have short sarcomeres (3.5+/-0.4 microm) characteristic of fast fibers and appear to be glycolytic. Each fiber type is characterized by several different myofibrillar protein isoforms including multiple isoforms of myosin heavy chain (MHC), troponin I (TnI), troponin T (TnT) and a crustacean fast muscle protein, P75. Three different isoforms of MHC are differentially expressed in the muscles, with fibers of the mid-region always co-expressing two isoforms at a 1:1 ratio within single fibers. Based on our analyses, we propose that these muscles are functionally divided into a two-geared system, with the aerobic fibers used for slow sustained activities and the glycolytic mid-region fibers being reserved for explosive sprints. Finally, we identified subtle differences in myofibrillar isoform expression correlated with crab body size, which changes by several orders of magnitude during an animal's lifetime.

Twelve actin-encoding cDNAs from the American lobster, Homarus americanus: cloning and tissue expression of eight skeletal muscle, one heart, and three cytoplasmic isoforms

Lobster muscles express a diverse array of myofibrillar protein isoforms. Three fiber types (fast, slow-twitch or S1, and slow-tonic or S2) differ qualitatively and quantitatively in myosin heavy and light chains, troponin-T, -I, and -C, paramyosin, and tropomyosin variants. However, little is known about the diversity of actin isoforms present in crustacean tissues. In this report we characterized cDNAs that encode twelve actin isoforms in the American lobster, Homarus americanus: eight from skeletal muscle (Ha-ActinSK1-8), one from heart (Ha-ActinHT1), and three cytoplasmic type actins from hepatopancreas (Ha-ActinCT1-3). All twelve cDNAs were products of distinct genes, as indicated by differences in the 3'-untranslated regions (UTRs). The open reading frames specified polypeptides 376 or 377 amino acids in length. Although key amino residues are conserved in the lobster actins, variations in nearby sequences may affect actin polymerization and/or interactions with other myofibrillar proteins. Quantitative reverse transcription-polymerase chain reaction showed muscle fiber type- and tissue-specific expression patterns. Ha-Actin-HT1 was expressed exclusively in heart (87% of the total; 12% of the total was Ha-ActinCT1). Ha-ActinCT1 was expressed in all tissues, while CT2 and CT3 were expressed only in hepatopancreas, with Ha-ActinCT2 as the major isoform (93% of the total). Ha-ActinSK1 and SK2 were the major isoforms (88% and 12% of the total, respectively) in the S1 fibers of crusher claw closer muscle. Fast fibers in the cutter claw closer and deep abdominal muscles differed in SK isoforms. Ha-ActinSK3, SK4, and SK5 were the major isoforms in cutter claw closer muscle (12%, 48%, and 37% of the total, respectively). Ha-ActinSK5 and SK8 were the major isoforms in deep abdominal flexor (31% and 65% of the total, respectively) and extensor (46% and 53% of the total, respectively) muscles, with SK6 and SK7 expressed at low levels. These data indicate that fast fibers in cutter claw and abdominal muscles show a phenotypic plasticity with respect to the expression of actin isoforms and may constitute discrete subtypes that differ in contractile properties.

Elasticity, unexpected contractility and the identification of actin and myosin in lobster arteries

Lobster arteries, which exhibit non-uniform elasticity when stretched, have a trilaminar organization. The inner layer is an elastic connective tissue and the outer layer is a collagenous connective tissue; the middle layer of an artery is an aggregation of cells containing microfilaments. Arterial cells possess actin, myosin and tropomyosin. Except for the dorsal abdominal artery,striated muscle cells are not evident in the walls of any of the vessels. The neurotransmitter glutamic acid and the neurohormone proctolin elicit slow circumferential contractions in all of the arteries leaving the lobster heart. Only the dorsal abdominal artery contracts when stimulated electrically. Longitudinal strips of the arteries do not respond to either drugs or electrical stimulation. Arterial contraction will have profound effects on resistance to blood flow and may be an important component of the control mechanisms regulating blood distribution.

Muscle-specific calpain is localized in regions near motor endplates in differentiating lobster claw muscles

Calpains are Ca2+-dependent proteinases that mediate protein turnover in crustacean skeletal muscles. We used an antibody directed against lobster muscle-specific calpain (Ha-CalpM) to examine its distribution in differentiating juvenile lobster claw muscles. These muscles are comprised of both fast and slow fibers early in development, but become specialized into predominantly fast or exclusively slow muscles in adults. The transition into adult muscle types requires that myofibrillar proteins specific for fast or slow muscles to be selectively removed and replaced by the appropriate proteins. Using immunohistochemistry, we observed a distinct staining pattern where staining was preferentially localized in the fiber periphery along one side of the fiber. Immunolabeling with an antibody directed against synaptotagmin revealed that the calpain staining was greatest in the cytoplasm adjacent to synaptic terminals. In complementary analyses, we used sequence-specific primers with real-time PCR to quantify the levels of Ha-CalpM in whole juvenile claw muscles. These expression levels were not significantly different between cutter and crusher claws, but were positively correlated with the expression of fast myosin heavy chain. The anatomical localization of Ha-CalpM near motor endplates, coupled with the correlation with fast myofibrillar gene expression, suggests a role for this intracellular proteinase in fiber type switching.

Molt-inhibiting hormone from the tropical land crab, Gecarcinus lateralis: cloning, tissue expression, and expression of biologically active recombinant peptide in yeast

Molt-inhibiting hormone (MIH), a member of the crustacean hyperglycemic neuropeptide hormone family, inhibits ecdysteroidogenesis in the molting gland or Y-organ (YO). A cDNA encoding MIH of the land crab (Gel-MIH) was cloned from eyestalk ganglia (EG) by a combination of reverse transcriptase polymerase chain reaction (RT-PCR) and 3'- and 5'-rapid amplification of cDNA ends (RACE). The cDNA (1.4 kb) encoded MIH prohormone containing a 35 amino acid signal peptide and a 78 amino acid mature peptide. The mature peptide had the six cysteines, one glycine, two arginines, one aspartate, one phenylalanine, and one asparagine in identical positions in the highly conserved sequence characteristic of other crustacean MIHs. Gel-MIH was expressed only in the EG, as determined by RT-PCR; it was not detected in Y-organ, heart, integument, gill, testis, ovary, hepatopancreas, thoracic ganglion, or skeletal muscle. A cDNA encoding the mature peptide was used to express recombinant MIH (rMIH) using a yeast (Pichia pastoris) expression system. Two constructs were designed to yield either a mature MIH fusion protein with a c-myc epitope and histidine (His) tag at the carboxyl terminus or an untagged mature protein without the c-myc and His sequences. Immunoreactive peptides were detected in Western blots of the cell culture media with both MIH constructs, indicating secretion of the processed rMIH into the medium. Culture media containing the untagged mature peptide significantly inhibited ecdysteroid secretion by YOs from land crab and green crab (Carcinus maenas) cultured in vitro, indicating that the Gel-rMIH was biologically active.

Myofibrillar gene expression in differentiating lobster claw muscles

Lobster claw muscles undergo a process of fiber switching during development, where isomorphic muscles containing a mixture of both fast and slow fibers, become specialized into predominantly fast, or exclusively slow, muscles. Although this process has been described using histochemical methods, we lack an understanding of the shifts in gene expression that take place. In this study, we used several complementary techniques to follow changes in the expression of a number of myofibrillar genes in differentiating juvenile lobster claw muscles. RNA probes complementary to fast and slow myosin heavy chain (MHC) mRNA were used to label sections of 7th stage (approximately 3 months old) juvenile claw muscles from different stages of the molt cycle. Recently molted animals (1-5 days postmolt) had muscles with distinct regions of fast and slow gene expression, whereas muscles from later in the molt cycle (7-37 days postmolt) had regions of fast and slow MHC expression that were co-mingled and indistinct. Real-time PCR was used to quantify several myofibrillar genes in 9th and 10th stages (approximately 6 months old) juvenile claws and showed that these genes were expressed at significantly higher levels in the postmolt claws, as compared with the intermolt and premolt claws. Finally, Western blot analyses of muscle fibers from juvenile lobsters approximately 3 to 30 months in age showed a shift in troponin-I (TnI) isoform expression as the fibers differentiated into the adult phenotypes, with expression of the adult fast fiber TnI pattern lagging behind the adult slow fiber TnI pattern. Collectively, these data show that juvenile and adult fibers differ both qualitatively and quantitative in the expression of myofibrillar proteins and it may take as much as 2 years for juvenile fibers to achieve the adult phenotype.

Three calpains and ecdysone receptor in the land crab Gecarcinus lateralis: sequences, expression and effects of elevated ecdysteroid induced by eyestalk ablation

Crustacean muscle has four calpain-like proteinase activities (CDP I, IIa, IIb and III) that are involved in molt-induced claw muscle atrophy, as they degrade myofibrillar proteins in vitro and in situ. Using PCR cloning techniques, three full-length calpain cDNAs (Gl-CalpB, Gl-CalpM and Gl-CalpT) were isolated from limb regenerates of the tropical land crab Gecarcinus lateralis. All three had highly conserved catalytic (dII) and C2-like (dIII) domains. Gl-CalpB was classified as a typical, or EF-hand, calpain, as the deduced amino acid sequence had a calmodulin-like domain IV in the C-terminus and was most similar to Drosophila calpains A and B. Based on its estimated mass (approximately 88.9 kDa) and cross-immunoreactivity with a polyclonal antibody raised against Dm-CalpA, Gl-CalpB may encode CDP IIb, which is a homodimer of a 95-kDa subunit. It was expressed in all tissues examined, including skeletal muscle, heart, integument, gill, digestive gland, hindgut, nerve ganglia, gonads and Y-organ (molting gland). Both Gl-CalpM and Gl-CalpT were classified as atypical, or non-EF-hand, calpains, as they lacked a domain IV sequence. Gl-CalpM was a homolog of Ha-CalpM from lobster, based on similarities in deduced amino acid sequence, estimated mass (approximately 65.2 kDa) and structural organization (both were truncated at the C-terminal end of dIII). It was expressed at varying levels in most tissues, except Y-organ. Gl-CalpT (approximately 74.6 kDa) was similar to TRA-3 in the nematode Caenorhabditis elegans; domain IV was replaced by a unique ;T domain' sequence. It was expressed in most tissues, except eyestalk ganglia and Y-organ. The effects of elevated ecdysteroid, induced by eyestalk ablation, on calpain and ecdysone receptor (Gl-EcR) mRNA levels in skeletal muscles were quantified by real-time PCR. At 1 day after eyestalk ablation, Gl-EcR and Gl-CalpT mRNA levels increased 15- and 19.3-fold, respectively, in claw muscle but not in thoracic muscle. At 3 days after eyestalk ablation, Gl-EcR and Gl-CalpT mRNA levels in claw muscle had decreased to 2.8-fold and 4.3-fold higher than those in intact controls, respectively, suggesting a feedback inhibition by ecdysteroid. There was no significant effect of eyestalk ablation on Gl-CalpB and Gl-CalpM mRNA levels. Gl-CalpT and Gl-EcR mRNA levels were significantly correlated in both claw and thoracic muscles from intact and eyestalk-ablated animals. The data suggest that Gl-CalpT is involved in initiation of claw muscle atrophy by ecdysteroids. Premolt reduction in claw muscle mass and concomitant remodeling of the sarcomere probably result from post-transcriptional regulation of calpains.

Hypersensitivity to Forcipomyia taiwana (biting midge): clinical analysis and identification of major For t 1, For t 2 and For t 3 allergens

BACKGROUND

Forcipomyia taiwana is a tiny, blood-sucking midge that cause intense pruritus and swelling in sensitive individuals. It is distributed island-wide in rural Taiwan and Southern China.

OBJECTIVE

This study aimed to study the allergic immune responses and identify F. taiwana allergens.

METHODS

Crude whole body F. taiwana extracts were prepared with phosphate-buffered saline. The specific IgE antibody was determined by enzyme-linked immunoassay and immunoblotting. Protein was analyzed by electrospray ionization tandem mass spectrometry.

RESULTS

Among the 372 subjects that were exposed to F. taiwana bites, 179 (48%) reported an immediate skin reaction with/without delay reaction and 41(11.1%) reported a solely delay reaction. The skin of 21 subjects was tested with F. taiwana extract. Of these 21 subjects, 12 (57.1%) produced immediate skin reactions and contained high levels of specific IgE antibody against F. taiwana. Immunoblotting revealed that 11 allergenic components are able to bind specific IgE. Allergens of 22, 24, 35, 36, and 64 kDa bound 50, 50, 75, 66.7, and 75% of IgE-containing sera tested, respectively. Tryptic fragments of the 24, 35, 36, and 64 kDa allergens were analyzed by ESI-MS/MS. Selected tryptic peptides of 24, 35, and 36, and 64 kDa allergens exhibited significant sequence identity with triosephosphate isomerase of Anopheles merus,Tenebrio molitor,Ochlerotatus togoi, and Chrysops vittatus, fructose 1,6-bisphosphate aldolase of Antheraea yamamai and Homalodisca coagulata, and a slow muscle myosin S1 heavy chain of Homarusamericanus and a protein with unknown function from A. gambiae, respectively. The 35 and 36 kDa proteins may represent different isoforms of the fructose 1,6-bisphosphate aldolase.

CONCLUSION

We conclude that immediate reaction to F. taiwana bites is IgE mediated and the 24 (For t 1), 35 (For t 2), and 64 kDa (For t 3) proteins are candidates for major F. taiwana allergens. Further studies are needed to confirm these allergens.

Invertebrate Muscles: Muscle Specific Genes and Proteins

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Eyestalk ablation has little effect on actin and myosin heavy chain gene expression in adult lobster skeletal muscles

The organization of skeletal muscles in decapod crustaceans is significantly altered during molting and development. Prior to molting, the claw muscles atrophy dramatically, facilitating their removal from the base of the claw. During development, lobster claw muscles exhibit fiber switching over several molt cycles. Such processes may be influenced by the secretion of steroid molting hormones, known collectively as ecdysteroids. To assay the effects of these hormones, we used eyestalk ablation to trigger an elevation of circulating ecdysteroids and then quantified myofibrillar mRNA levels with real-time PCR and myofibrillar protein levels by SDS-PAGE. Levels of myosin heavy chain (MHC) and actin proteins and the mRNA encoding them were largely unaffected by eyestalk ablation, but in muscles from intact animals, myofibrillar gene expression was modestly elevated in premolt and postmolt animals. In contrast, polyubiquitin mRNA was significantly elevated (about 2-fold) in claw muscles from eyestalk-ablated animals with elevated circulating ecdysteroids. Moreover, patterns of MHC and actin gene expression are significantly different among slow and fast claw muscles. Consistent with these patterns, the three muscle types differed in the relative amounts of myosin heavy chain and actin proteins. All three muscles also co-expressed fast and slow myosin isoforms, even in fibers that are generally regarded as exclusively fast or slow. These results are consistent with other recent data demonstrating co-expression of myosin isoforms in lobster muscles.

Fiber polymorphism in skeletal muscles of the American lobster, Homarus americanus: continuum between slow-twitch (S1) and slow-tonic (S2) fibers

In recent years, an increasing number of studies has reported the existence of single fibers expressing more than one myosin heavy chain (MHC) isoform at the level of fiber proteins and/or mRNA. These mixed phenotype fibers, often termed hybrid fibers, are currently being recognized as the predominant fiber type in many muscles, and the implications of these findings are currently a topic of great interest. In a recent study, we reported single fibers from the cutter claw closer muscle of lobsters that demonstrated a gradation between the slow-twitch (S1) and slow-tonic (S2) muscle phenotype. In the present study, we focused on S1 and S2 fibers from the superficial abdominal muscles of the lobster as a model to study the continuum among muscle fiber types. Complementary DNAs (cDNA) encoding an S2 isoform of myosin heavy chain (MHC) and an S2 isoform of tropomyosin (Tm) were isolated from the superficial abdominal flexor muscles of adult lobsters. These identified sequences were used to design PCR primers used in conjunction with RT-PCR and real-time PCR to measure expression levels of these genes in small muscle samples and single fibers. The relative expression of the corresponding S1 MHC and S1 Tm isoforms was measured in the same samples with PCR primers designed according to previously identified sequences. In addition, we measured the relative proportions of MHC, troponin (Tn) T and I protein isoforms present in the same samples to examine the correlation of these proteins with one another and with the MHC and Tm mRNAs. These analyses revealed significant correlations among the different myofibrillar proteins, with the S1 and S2 fibers being characterized by a whole assemblage of myofibrillar isoforms. However, they also showed that small muscle samples, and more importantly single fibers, existed as a continuum from one phenotype to another. Most fibers possessed mixtures of mRNA for MHC isoforms that were unexpected based on protein analysis. These findings illustrate that muscle fibers in general may possess a phenotype that is intermediate between the extremes of 'pure' fiber types, not only at the MHC level but also in terms of whole myofibrillar assemblages. This study supports and extends our recent observations of mixed phenotype fibers in lobster claw and leg muscles. The existence of single fiber polymorphism in an invertebrate species underscores the generality of the phenomenon in skeletal muscles and emphasizes the need for an understanding of the proximal causes and physiological consequences of these intermediate fiber types.

Two fast-type fibers in claw closer and abdominal deep muscles of the Australian freshwater crustacean,Cherax destructor, differ in Ca2+ sensitivity and troponin-I isoforms

One type of fast fiber and two types of slow (slow-twitch, S1 and slow-tonic, S2) fibers are found in decapod crustacean skeletal muscles that differ in contractile properties and myofibrillar protein isoform compositions. In this study the structural characteristics, protein isoform compositions, and Ca2+-activation properties of fast fibers in the claw closer (F1) and abdominal deep flexor (F2) muscles of Cherax destructor were analyzed. For comparison, myofibrillar protein isoform compositions of slow (long-sarcomere) fibers from claw and abdomen were also determined; our results indicate that the slow fibers in the claw closer were the slow-twitch (S1) type and those in the abdominal superficial flexor were primarily slow-tonic (S2) type. F1 fibers had shorter resting sarcomere lengths (2.93 microm in unstretched fibers and 3.06 microm in stretched fibers) and smaller fiber diameter (256 microm) than F2 fibers (sarcomere lengths 3.48 microm in unstretched and 3.46 microm in stretched; 747 microm diameter). Moreover, F1 fibers showed a narrower range in sarcomere lengths than F2 fibers (2.81 to 3.28 microm vs. 2.47 to 4.05 micro m in unstretched fibers). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting showed that the fast fibers from claw and abdomen differed in troponin-I composition; F1 fibers expressed two isoforms of troponin-I (TnI1 and TnI2) in approximately equal amounts, whereas F2 fibers expressed primarily TnI3 and lower levels of TnI1. F1 fibers were more sensitive to Ca2+, as shown by higher pCa values at threshold activation (pCa(10)=6.50+/-0.07) and at 50% maximum force (pCa(50)=6.43+/-0.07) than F2 fibers (pCa(10)=6.12+/-0.04 and pCa(50)=5.88+/-0.03, respectively). F1 fibers also had a greater degree of co-operativity in Ca2+ activation, as shown by a higher maximum slope of the force-pCa curve (n(Ca)=12.98+/-2.27 vs. 4.34+/-0.64). These data indicate that there is a greater fast fiber-type diversity in crustacean muscles than was previously supposed. Moreover, the differences in activation properties suggest that the TnI isoform composition influences the Ca2+ sensitivity of the contractile mechanism.