Morphological and physiological development of anterior thoracic stretch receptors in two isopods, <Emphasis Type="Italic">Armadillidium vulgare</Emphasis> and <Emphasis Type="Italic">Ligia exotica</Emphasis>

Abdominal muscle receptor organs (MROs) monitor the position and movement of abdomen in crustaceans. Thoracic segments of decapods are fused and immovable. It is speculated that MROs had retrograded simple shape, N-cells that lost receptor muscles, a receptor cell and accessory nerves. We focused on the effect of segmental movement in respect to thoracic N-cells and MROs in isopods that have movable thoracic segments. Armadillidium vulgare rolled up its body segments. Ligia exotica swam by quick movement of the posterior thoracic segments. Both isopods possessed N-cells and MROs in the thorax. N-cells were a simple structure, but N-cells from the second and third thoracic segments of A. vulgare had a muscle strand. MROs^T3–T4 (from the third and fourth thoracic segments) of A. vulgare had two receptor muscles. MROs^T3–T4 of L. exotica had one long receptor muscle. N-cells of both species and MROs of A. vulgare showed slowly adapting stretch-activated discharges. MROs of L. exotica showed both slowly and rapidly adapting discharges. The stretch-activated responses of N-cells and MROs inhibited each other. N-cells or MROs in the thorax of isopods are not related to the segmental structure. The morphology and physiology of N-cells and MROs are specialized to species–specific behaviors.     

Development and embryonic pattern of body wall musculature in the crassiclitellate Eisenia andrei (Annelida,Clitellata)

During early development of Eisenia andrei (Crassiclitellata), a loose arrangement of primary circular and longitudinal muscles encloses the whole embryo. Circular muscles differentiate in an anterior–posterior progression creating a segmental pattern. Primary circular muscles emerge at the segmental borders while later in development the central part of each segment is filled with circular strands. Longitudinal muscles develop in an anterio‐posterior manner as well, but by continuous lengthening. Muscle growth is not restricted by segmental boundaries. The development begins with one pair of prominent longitudinal muscles differentiating ventrally along the right and the left germ band. These first muscles provide a guiding structure for the parallel organization of the afterwards differentiating longitudinal musculature. Additional primary longitudinal muscles emerge and form, together with the initial circular muscles, the primary muscle grid of the embryo. During the following development, secondary longitudinal muscle strands develop and integrate themselves into the primary grid. Meanwhile the primary circular muscles split into thin strands in a ventral to dorsal progression. Thus, a fine structured mesh of circular and longitudinal muscles is generated. Compared to other “Oligochaeta”, embryonic muscle patterns in E. andrei are adapted to the development of a lecithotrophic embryo. Nevertheless, two general characteristics of annelid muscle development become evident. The first is the segmental development of the circular muscles from a set of initial muscles situated at the segment borders. Second, there is a continuous development of primary longitudinal muscles starting at the anterior pole. At least one pair of main primary longitudinal strands is characteristic in Annelida. The space between all primary strands is filled with secondary longitudinal strands during further development. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Embryonic expression of muscle-specific antigens in the grasshopper Schistocerca gregaria

Monoclonal antibodies (MAbs) are used to investigate molecules that are expressed during embryonic muscle differentiation and that may be involved in muscle pioneer and muscle attachment site formation. MAb F2A5 immunoreactivity appears in all muscle pioneers as soon as they extend processes, and continues in all muscle precursors. MAb 4H1 immunoreactivity is strongly expressed only after mesodermal cells have fused with the muscle pioneers; then it is concentrated at their growth-cone-like ends near developing attachment sites. During later embryonic development, MAb F2A5 and MAb 4H1 immunoreactivity become associated with the myofibrillar network. Biochemical experiments indicate that MAb 4H1 recognises a 47 kDa antigen, and MAb F2A5 recognises an 80 kDa antigen.     

The pregenital abdominal musculature in phasmids and its implications for the basal phylogeny of Phasmatodea (Insecta: Polyneoptera)

Recently several conflicting hypotheses concerning the basal phylogenetic relationships within the Phasmatodea (stick and leaf insects) have emerged. In previous studies, musculature of the abdomen proved to be quite informative for identifying basal taxa among Phasmatodea and led to conclusions regarding the basal splitting events within the group. However, this character complex was not studied thoroughly for a representative number of species, and usually muscle innervation was omitted. In the present study the musculature and nerve topography of mid-abdominal segments in both sexes of seven phasmid species are described and compared in detail for the first time including all putative basal taxa, e.g. members of Timema, Agathemera, Phylliinae, Aschiphasmatinae and Heteropteryginae. The ground pattern of the muscle and nerve arrangement of mid-abdominal segments, i.e. of those not modified due to association with the thorax or genitalia, is reconstructed. In Timema, the inner ventral longitudinal muscles are present, whereas they are lost in all remaining Phasmatodea (Euphasmatodea). The ventral longitudinal muscles in the abdomen of Agathemera, which span the whole length of each segment, do not represent the plesiomorphic condition as previously assumed, but might be a result of secondary elongation of the external ventral longitudinal muscles. Sexual dimorphism, common within the Phasmatodea, also applies to the muscle arrangement in the abdomen of some species. Only in the females of Haaniella dehaanii (Heteropteryginae) and Phyllium celebicum (Phylliinae) the ventral external longitudinal muscles are elongated and span the length of the whole segment, possibly as a result of convergent evolution.     

Homonomies within the ventral muscle system and the associated motoneurons in the locust,Schistocerca gregaria (Insecta,Caelifera)

To understand the segmental reiteration of an insect, the serially arranged neuromuscular system of the locust, Schistocerca gregaria, is studied. The ventral muscle system is chosen and its motoneuronal supply is described in the thoracic and pregenital segments. In general, repetitively arranged, similar sets of motoneurons (MNs) supply the ventral muscles of these segments. Common criteria of both topology of muscles and neural features (nerve branches and motoneuronal supply) suggest possible homonomies of the ventral longitudinal muscles and ventral diaphragm of the thoracic and abdominal system. Based on a segment-by-segment analysis, muscle topology and motor supply match, in most instances. There are, however, cases where such a parallelism is missing. In a particular cases the supply of apparently homonomous muscles shifts from one set of MNs to another. In another case, putatively equivalent MNs of different ganglia supply morphologically different muscle structures in the adult animal. Therefore, it becomes apparent that muscles and their supplying MNs are, in principle, independent elements which might be subjected autonomously to ontogenetic processes. As a consequence, in the search for the basic segmental Bauplan depending on homonomous structures, muscles and MNs have to be regarded as separate entities.Abbreviations A1–6 abdominal ganglion (or neuromere A1–3) - AS1–6 abdominal segment 1–6 - DUM doisal unpaired median - M muscle (number) - MN motoneuron - N nerve (number) - PMN paramedian nerve - T1–3 pro-, meso-, metathoracic ganglion - TS1–3 pro-, meso-, metathoracic segment - VD ventral diaphragm - VM ventral muscle     

Induced neuroma formation and target muscle perturbation in the giant fiber pathway of the Drosophila temperature-sensitive mutant shibire

Summary The temperature-sensitive mutation shibire (shi) in Drosophila melanogaster is thought to disrupt membrane recycling processes, including endocytotic vesicle pinch-off. This mutation can perturb the development of nerves and muscles of the adult escape response. After exposure to a heat pulse (6 h at 30° C) at 20 h of pupal development, adults have abnormal flight muscles. Wing depressor muscles (DLM) are reduced in number from the normal six to one or two fibers, and are composed of enlarged fibers that appear to represent fiber fusion; large spaces devoid of muscle fibers suggested fiber deletion. The normal five motor axons are present in the peripheral nerve PDMN near the ganglion. However, while some motor axons pass dorsally to the extant fibers, other motor axons lacking end targets pass into an abnormal posterior branch and terminate in a neuroma, i.e., a tangle of axons and glia without muscle target tissue. Hemisynapses are common in axons of the proximal PDMN and within the neuroma, but they are rarely seen in control (no heat pulse) shi or wild-type flies. All surviving muscle fibers are innervated; no muscle tissue exists without innervation. Fibrillar fine structure and neuromuscular synapses appear normal. Fused fibers have dual innervation, suggesting correct and specific matching of target tissue and motor axons. Motor axons lacking target fibers do not innervate erroneous targets but instead terminate in the neuroma. These results suggest developmental constraints and rules, which may contribute to the orderly, stereotyped development in the normal flight system. The nature of the anomalies inducible in the flight motor system in shi flies implies that membrane recycling events at about 20 h of pupal development are critical to the formation of the normal adult nerve-muscle pattern for DLM flight muscles.     

Motor supply of the dorsal longitudinal muscles,I: homonomy and ontogeny of the motoneurones in locusts (Insecta,Caelifera)

The neural supply of the dorsal lingitudinal muscles in successive segments from the prothorax to the pregenital abdomen of adult and larval instar locusts (Locusta migratoria and Schistocerca gregaria) has been studied. Stainings have also been carried out for embryos. The whole complement consists of three muscles, of which one or both of the smaller ones degenerate in the pterothoracic segments during early imaginal life. Based on morphological criteria, several motoneurone types can be distinguished. The neural set is almost identical for all segments, independent of the general organization of each segment. At about 65% of embryogenesis, all neurone types can be identified with respect to soma position and basic features of the central branching pattern. By the end of embryogenesis, a dendritic pattern is established which resembles the adult pattern in all major aspects. The reiteration of homonomous elements suggests that they form part of the basic segmental neural Bauplan generated early in embryogenesis. This study of muscles and motoneurones forming identifiable, reiterated neuromuscular units can serve as a segmental matrix for a comparative study comprising other phylogenetic groups of the Tracheata.Abbreviations DLM dorsal longitudinal muscle - DUM dorsal unpaired median - M muscle (number) - MN motoneurone - N nerve (number)     

Delta-sarcoglycan is necessary for early heart and muscle development in zebrafish

Delta-sarcoglycan, one member of the sarcoglycan complex, is a very conservative muscle-specific protein exclusively expressed in the skeletal and cardiac muscles of vertebrates. Mutations in sarcoglycans are known to be involved in limb-girdle muscular dystrophy (LGMD) and dilated cardiomyopathy (DCM) in humans. To address the role of delta-sarcoglycan gene in zebrafish development, we have studied expression pattern of delta-sarcoglycan in zebrafish embryos and examined the role of delta-sarcoglycan in zebrafish embryonic development by morpholino. Strong expression of delta-sarcoglycan was observed in various muscles including those of the segment, heart, eye, jaw, pectoral fin, branchial arches, and swim bladder in zebrafish embryo. Delta-sarcoglycan was also expressed in midbrain and retina. Knockdown of delta-sarcoglycan resulted in severe abnormality in both the cardiac and skeletal muscles. Some severe ones displayed serious morphological abnormality such as hypoplastic head, linear heart, very weak heartbeats, and runtish trunk, all dead within 5 dpf. Whole-mount in situ hybridization analysis showed that adaxial cells and muscle pioneers were affected in delta-sarcoglycan knockdown embryos. In addition, absence of delta-sarcoglycan protein severely delayed the cardiac development and influenced the differentiation of cardiac muscle, and the cardiac left-right asymmetry was dramatically changed in morpholino-treated embryos. These data together suggest that delta-sarcoglycan plays an important role in early heart and muscle development.     

Vestigial Is Required during Late-Stage Muscle Differentiation in Drosophila melanogaster Embryos

The somatic muscles of Drosophila develop in a complex pattern that is repeated in each embryonic hemi-segment. During early development, progenitor cells fuse to form a syncytial muscle, which further differentiates via expression of muscle-specific factors that induce specific responses to external signals to regulate late-stage processes such as migration and attachment. Initial communication between somatic muscles and the epidermal tendon cells is critical for both of these processes. However, later establishment of attachments between longitudinal muscles at the segmental borders is largely independent of the muscle–epidermal attachment signals, and relatively little is known about how this event is regulated. Using a combination of null mutations and a truncated version of Sd that binds Vg but not DNA, we show that Vestigial (Vg) is required in ventral longitudinal muscles to induce formation of stable intermuscular attachments. In several muscles, this activity may be independent of Sd. Furthermore, the cell-specific differentiation events induced by Vg in two cells fated to form attachments are coordinated by Drosophila epidermal growth factor signaling. Thus, Vg is a key factor to induce specific changes in ventral longitudinal muscles 1–4 identity and is required for these cells to be competent to form stable intermuscular attachments with each other.     

Fibre types in the locomotory muscles of an antarctic teleost,Notothenia rossii

Summary The metabolic and structural differentiation of locomotory muscles of Notothenia rossii has been investigated. In this species sustained locomotion is achieved by sculling with enlarged pectoral fins (labriform locomotion), whilst the segmental myotomal muscle is reserved for burst activity. Red, white and subepidermal fibres can be distinguished in the trunk by histochemical and ultrastructural criteria. The main pectoral muscle (m. adductor profundus) consists entirely of red fibres. These three main fibres types show differences in histochemical staining profiles, capillarization, myofibril shape and packing, and lipid and mitochondrial content. The fractional volume of mitochondria amounts to 38% for pectoral, 30% for red myotomal and 1.9% for white myotomal fibres. Enzyme activities of red pectoral muscle are consistent with a higher potential for aerobic glucose and fatty acid oxidation than for the red myotomal fibres. Mg²⁺ Ca²⁺ -myofibrillar ATPase activities are similar for red pectoral and myotomal muscles and approximately half of those white fibres. Specialisations of N. rossii muscles associated with labriform swimming and locomotion at Antarctic temperatures are discussed.     

Homeotic gene function in the muscles of Drosophila larvae

The segmental musculature of Drosophila melanogaster larvae consists of 24-30 muscles per segment. Unique patterns of muscles are found in the three thoracic segments and the first and last abdominal segments; the remaining abdominal segments share the same pattern. Mutations in Ultrabithorax (Ubx) cause partial transformation of the muscle pattern of larval abdominal segments towards metathorax. The muscles of the thorax are not affected. In the first two abdominal segments the changes include the loss of at least 11 `abdominal' muscles and the gain of 11 `thoracic' muscles. Less extensive transformations are seen in more posterior abdominal segments. Anterobithorax, bithorax, postbithorax and bithoraxoid mutations also induce transformations of the larval musculature. Each allelic group affects a domain that is a subset of the entire Ubx domain but these domains are not restricted to compartments or segments and may extend through as many as five segments. In the muscles the segmental distribution of Ubx antigen correlates with the segments affected by Ubx mutations. The different domains of Ubx in mesoderm and ectoderm argue that the segmental diversity of the muscle pattern is not simply induced by the overlying epidermis and that Ubx function in the mesoderm is required for the correct development of abdominal segments.     

Complex innervation of three neck muscles by motor and dorsal unpaired median neurons in crickets

Summary In the crickets, Gryllus campestris and Gryllus bimaculatus, the innervation of the dorso-ventral neck muscles M62, M57, and M59 was examined using cobalt staining via peripheral nerves and electrophysiological methods. M62 and M57 are each innervated by two motoneurons in the suboesophageal ganglion. The four motoneurons project into the median nerve to bifurcate into the transverse nerves of both sides. M62 and M57 are the only neck muscles innervated via this route. These bifurcating axon-projections are identical to those of the spiracular motoneurons in the prothoracic ganglion innervating the opener and closer muscle of the first thoracic spiracle in the cricket. The morphology of their branching pattern is described. The neck muscle M57 and the opener muscle of the first thoracic spiracle are additionally innervated by one mesothoracic motoneuron each, with similar morphology. These results suggest, that in crickets, the neck muscles M57 and M62 are homologous to spiracular muscles in the thoracic segments. The two neck muscles M62 and M59 (the posterior neighbour of M57) receive projections from a prothoracic dorsal unpaired median (DUM) neuron that also innervates dorsal-longitudinal neck muscles but not M57. In addition, one or two mesothoracic DUM neurons send axon collaterals intersegmentally to M59. This is the first demonstration of the innervation of neck muscles by DUM neurons.     

Longitudinal body wall muscles are electrically coupled across the segmental boundary in the third instar larva ofDrosophila melanogaster

Longitudinal body wall muscles in the third instar larva of the fruitfly,Drosophila melanogaster, were systematically examined for electrical and dye coupling. These muscle cells were found to be electrically coupled but rarely dye-coupled across the segmental boundary. The inter-segmental coupling coefficients between muscle #6s and muscle #7s across the segmental boundary were 0.33 ± 0.09 (mean ± S.D.,n = 12) and 0.43 ± 0.09 (n = 5), respectively, which are much larger than values previously reported inDrosophila but similar to those reported in the blowfly and hawkmoth. By contrast, the intra-segmental coupling coefficient between muscles #6 and #7 was smaller, 0.16 ± 0.08 (n = 28). Other muscle cells which had apparent physical contacts with these longitudinal muscles were examined but were not electrically coupled to them. Nerve-evoked as well as miniature excitatory junctional potentials were found also electrotonically spread across the segmental boundary. The inter-segmental coupling between muscle #6s was not blocked by the gap junction inhibitors halothane or 1-octanol. Functional significance of this electrical coupling is apparently in coordination of larval body movements.     

Functional morphology of the muscles in Philodina sp. (Rotifera: Bdelloidea)

Whole-mounts of Philodina sp., a bdelloid rotifer, were stained with fluorescent-labeled phalloidin to visualize the musculature. Several different muscle types were identified including incomplete circular bands, coronal retractors and foot retractors. Based on the position of the larger muscle bands in the body wall, their function during creeping locomotion and tun formation was inferred. Bdelloid creeping begins with the contraction of incomplete circular muscle bands against the hydrostatic pseudocoel, resulting in an anterior elongation of the body. One or more sets of ventral longitudinal muscles then contract bringing the rostrum into contact with the substrate, where it presumably attaches via adhesive glands. Different sets of ventral longitudinal muscles, foot and trunk retractors, function to pull the body forward. These same longitudinal muscle sets are also used in `tun' formation, in which the head and foot are withdrawn into the body. Three sets of longitudinal muscles supply the head region (anterior head segments) and function in withdrawal of the corona and rostrum. Two additional pairs of longitudinal muscles function to retract the anterior trunk segments immediately behind the head, and approximately five sets of longitudinal retractors are involved in the withdrawal of the foot and posterior toes. To achieve a greater understanding of rotifer behavior, it is important to elucidate the structural complexity of body wall muscles in rotifers. The utility of fluorescently-labeled phalloidin for the visualization of these muscles is discussed and placed in the context of rotifer functional morphology.     

The fate of specific motoneurons and sensory neurons of the pregenital abdominal segments inTenebrio molitor (Insecta : Coleoptera) during metamorphosis

The anatomy and innervation of the lateral external muscle and sensory cells located in the ventral region of pregenital abdominal segments were examined at the larval and adult stages ofTenebrio molitor (Coleoptera). All seven muscles located in this region degenerate during the pupal stage, whilst only the lateral external median (lem) appears in the adult. Backfillings of the motor nerve innervating this muscle reveal that, at both larval and adult stages, it is innervated by ten neurons. Intracellular records from the muscle fibres show that two neurons are inhibitory, and at least five are excitatory. There are also two unpaired neurons. A variety of sensory organs are located in the ventral region of the larvae, whilst only campaniform sensilla are found in the adult. At both stages, the innervation pattern of the sensory nerve branches is very similar. Also, the central projections of the sensory cells occupy similar neuropilar areas. Finally, prolonged intracellular records from the lem muscle revealed that, at the larval stage, it participates only in segmental or intersegmental reflexes, whilst in the adult it has a primary expiratory role in ventilation. The results show that extensive changes occur in the number of muscles located in the ventral region of the pregenital abdominal segments, as well as in the arrangement and number of sensory neurons, in the structure of the exoskeleton, and even in the central nervous system. In contrast, only minor changes are observed in the sensory and motor nerve branches, in the sensory projections, and in the number and the location of the motoneurons innervating the lateral external median muscle. Correspondence to: G. Theophilidis     

Muscle activity underlying sexual behaviour in male locusts (Locusta migratoria) after normal and hormonally disturbed development

Abstract. . The activities of three sets of muscles, representing the major components of the abdominal muscle system, were recorded in the pregenital abdominal segments of adult males of Locusta migratoria. The muscular activities were associated with three consecutive actions of the male's mating behaviour: abdominal lowering, S-bending and hooking-up. These three actions depend mainly on the relative coordination of the dorsal versus ventral longitudinal muscles; the activity of the dorsoventral muscles is rather unpredictable, except in the sixth and seventh abdominal segments where they are regularly involved in hooking-up. Studies on male sexual behaviour-linked muscle activity in precocene-induced fifth-instar adultiforms and azadirachtin-induced fifth-instar over-aged nymphs revealed no distinct differences between these creatures and normal mature males. Therefore the muscle activities associated with these adult-specific behavioural acts can be released precociously, i.e. their occurrence is not dependent on a distinct series of instars. Moreover, the results obtained with over-aged nymphs demonstrate that morphogenesis and ethogenesis (i.e. formation of neural circuits controlling adult-specific behaviour) are not closely dependent on each other.     

Developmental transition of touch response from slow muscle-mediated coilings to fast muscle-mediated burst swimming in zebrafish

It is well known that slow and fast muscles are used for long-term sustained movement and short bursts of activity, respectively, in adult animal behaviors. However, the contribution of the slow and fast muscles in early animal movement has not been thoroughly explored. In wild-type zebrafish embryos, tactile stimulation induces coilings consisting of 1–3 alternating contractions of the trunk and tail at 24 hours postfertilization (hpf) and burst swimming at 48 hpf. But, embryos defective in flightless I homolog (flii), which encodes for an actin-regulating protein, exhibit normal coilings at 24 hpf that is followed by significantly slower burst swimming at 48 hpf. Interestingly, actin fibers are disorganized in mutant fast muscle but not in mutant slow muscle, suggesting that slower swimming at 48 hpf is attributable to defects of the fast muscle tissue. In fact, perturbation of the fast muscle contractions by eliminating Ca²⁺ release only in fast muscle resulted in normal coilings at 24 hpf and slower burst swimming at 48 hpf, just as flii mutants exhibited. In contrast, specific inactivation of slow muscle by knockdown of the slow muscle myosin genes led to complete loss of coilings at 24 hpf, although normal burst swimming was retained by 48 hpf. These findings indicate that coilings at 24 hpf is mediated by slow muscle only, whereas burst swimming at 48 hpf is executed primarily by fast muscle. It is consistent with the fact that differentiation of fast muscle follows that of slow muscle. This is the first direct demonstration that slow and fast muscles have distinct physiologically relevant contribution in early motor development at different stages.     

Differentiation of metaxylem cell line in the root ofAllium cepa L.

Summary The differentiation processes of the metaxylem cell line in the root ofAllium cepa are characterized by amplification phenomena of repetitive DNA sequences mainly localized in heterochromatic regions of metaphase chromosomes. Moreover, these sequences are heavily methylated. This paper presents additional results on variation in endogenous DNA methylation in different developing root segments. The results show that methylation is higher in apical meristematic cells than the differentiating segments; contrastingly, total RNA synthesis seems to be correlated with undermethylation. Addition of labelled methyl groups to DNA by eukaryotic methylase, DNA digestions with different restriction enzymes specific for methylated sites and HPLC analysis confirmed the above results. Moreover, variation in methylation levels during differentiation occur not only at the internal cytosine of the-CCG-sites, but also at external cytosine. Furthermore, methylation affects other sites containing the trinucleotides-CXG-. In conclusion, root differentiation inAllium cepa seems to be correlated with gene activation modulated by the methylation/demethylation of particular DNA sequences.     

Time course of changes in markers of myogenesis in overloaded rat skeletal muscles.

During the process of compensatory muscle hypertrophy, satellite cells are thought to proliferate, differentiate, and then fuse with existing myofibers. We hypothesized that early in this process changes occur in the expression of cellular markers indicative of the onset of myogenic processes. The plantaris muscles of rats were overloaded via the unilateral ablation of synergists. Groups of rats were killed at time points from 6 h to 12 days. Changes in muscle gene expression (mRNA) of cyclin D1, p21, myogenin, MyoD, and insulin-like growth factor I (IGF-I, mRNA and peptide) were measured. Cyclin D1 (a cell cycle marker) was increased after 24 h of overloading and corresponded with changes in muscle DNA content. In contrast, p21 and myogenin, markers of cellular differentiation, were increased after just 12 h. Muscle IGF-I peptide levels were also increased at early time points. The results of this study indicate that myogenic processes are activated in response to increased loading at very early time points (e.g., 12 h) and that IGF-I may be modulating this response. Furthermore, these findings suggest that some cells may have been differentiating very early in the adaptation process before events leading to cellular proliferation have been initiated.