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PubMed2006

Intrinsic chiral properties of the Xenopus egg cortex: an early indicator of left-right asymmetry?

Vertebrate embryos define an anatomic plane of bilateral symmetry by establishing rudimentary anteroposterior and dorsoventral (DV) axes. A left-right (LR) axis also emerges, presaging eventual morphological asymmetries of the heart and other viscera. In the radially symmetric egg of Xenopus laevis, the earliest steps in DV axis determination are driven by microtubule-dependent localization of maternal components toward the prospective dorsal side. LR axis determination is linked in time to this DV-determining process, but the earliest steps are unclear. Significantly, no cytoskeletal polarization has been identified in early embryos capable of lateral displacement of maternal components. Cleaving Xenopus embryos and parthenogenetically activated eggs treated with 2,3-butanedione monoxime (BDM) undergo a dramatic large-scale torsion, with the cortex of the animal hemisphere shearing in an exclusively counterclockwise direction past the vegetal cortex. Long actin fibers develop in a shear zone paralleling the equator. Drug experiments indicate that the actin is not organized by microtubules, and depends on the reorganization of preexisting f-actin fibers rather than new actin polymerization. The invariant chirality of this drug response suggests a maternally inherited, microfilament-dependent organization within the egg cortex that could play an early role in LR axis determination during the first cell cycle. Consistent with this hypothesis, brief disruption of cortical actin during the first cell cycle randomizes the LR orientation of tadpole heart and gut.

Actins↗

PubMed1979

Ingrowth and ramification of retinal fibers in the developing optic tectum of the chick embryo.

Onset, temporal sequence, and pattern of ingrowth of retinal fibers into the developing optic tectum of the chicken were investigated with histological procedures including the Golgi technique. Invading fibers could first be detected by stage 34 (eight days of incubation) at a specific locus which is the central area of the optic tectum. Compared to other tectal regions the central area is distinguished at this time by its advanced cytoarchitectural development and by the maturation of dendrites of radial cells located within superficial laminae. Immediately after their arrival at the central area some fibers can be observed invading the outer tectal layers and forming side branches. These observations permit the conclusion that fibers do not wait at their termination site for several days, as has been suggested earlier. Retinal axons start to invade the tectum at the site which is most advanced in its structural development. This early maturation of neurons in a specific tectal region might be a sufficient explanation for the central retinal fibers connecting to neurons of this area, which, propter hoc, is called the central tectal area.

Age Factors↗

PubMed1981

[Fragmentation of the myocardium: facts and hypotheses].

Histological examination of the myocardium in section and operation material and in experimental animals allowed two different types of its fragmentation to be distinguished. Type I is characterized by cellular dissociation of the muscle fibers, develops during life and may be accompanied by stromal reaction ending in sclerosis. Type II is of artificial nature and depends both on the direction of microtoming of the muscle fibers and on their increased fragility the nature of which is obscure as yet. Combination of both types of fragmentation in the same muscle fibers makes difficult their distinct differentiation.

Adolescent↗

PubMed1997

Regulation of the chick cutaneous innervation pattern in retinoic acid-induced ectopic feathers and in the naked neck mutant.

In chick skin, nerve fibers develop in a typical network formed by arcades around the base of feathers. In this study, we tried to dissociate the morphogenesis of nerve arcades and feathers, and to clarify the implication of several matricial molecules in these two developmental events. For this purpose, cutaneous nerve pattern and distribution of fibronectin, tenascin, and three epitopes of chondroitin sulfate proteoglycans (CSPGs) have been immunohistologically studied in the skin of the specific apteria of naked neck chick mutants, which lack feathers in the neck area, and in the tarso-metatarsal zone of retinoic acid-treated embryos where ectopic feathers grow. The presence of feathers was always associated with nerve arcades; no arcades were present in featherless areas. Specific immunofluorescence for tenascin and two epitopes of CSPGs revealed different distributions in the naked-neck neo-apteria as compared to control apteria. Moreover, the only difference in matricial composition in ectopic feathers concerned a CSPG isoform, bringing additional evidence that extracellular matrix molecules, and especially some (but not all) CSPGs, are involved both directly and indirectly in the cutaneous nerve pattern development.

Animals↗

PubMed2006

Brain-derived neurotrophic factor induces post-lesion transcommissural growth of olivary axons that develop normal climbing fibers on mature Purkinje cells.

In the adult mammalian central nervous system, reinnervation and recovery from trauma is limited. During development, however, post-lesion plasticity may generate alternate paths providing models to investigate factors that promote reinnervation to appropriate targets. Following unilateral transection of the neonatal rat olivocerebellar pathway, axons from the remaining inferior olive reinnervate the denervated hemicerebellum and develop climbing fiber arbors on Purkinje cells. However, the capacity to recreate this accurate target reinnervation in a mature system remains unknown. In rats lesioned on day 15 (P15) or 30 and treated with intracerebellar injection of brain-derived neurotrophic factor (BDNF) or vehicle 24 h later, the morphology and organisation of transcommissural olivocerebellar reinnervation was examined using neuronal tracing and immunohistochemistry. In all animals BDNF, but not vehicle, induced transcommissural olivocerebellar axonal growth into the denervated hemicerebellum. The distribution of reinnervating climbing fibers was not confined to the injection sites but extended throughout the denervated hemivermis and, less densely, up to 3.5 mm into the hemisphere. Transcommissural olivocerebellar axons were organised into parasagittal microzones that were almost symmetrical to those in the right hemicerebellum. Reinnervating climbing fiber arbors were predominantly normal, but in the P30-lesioned group 10% were either branched within the molecular layer forming a smaller secondary arbor or were less branched, and in the P15 lesion group the reinnervating arbors extended their terminals almost to the pial surface and were larger than control arbors (P < 0.02). These results show that BDNF can induce transcommissural olivocerebellar reinnervation, which resembles developmental neuroplasticity to promote appropriate target reinnervation in a mature environment.

Afferent Pathways↗

PubMed1990

Mode of neuronal migration of the pontine stream in fetal mice.

The migration of immature neurons in the pontomedullary subpial region was examined in fetal mice by light and electron microscopy. Immature pontine cells were observed forming a cell strand from the ventral aspect of the fourth ventricle to the pontine flexure during the period between the 14th and 17th day of gestation. These cells were elongated and oriented parallel to the direction of migration, and displayed features of immature neurons: they contained a high concentration of ribosomal rosettes and a few cisternae of rough endoplasmic reticula, as well as Golgi apparatus, mitochondria, microtubules and centrioles. Many of the neurons extended leading processes, and these contained longitudinally-arrayed microtubules. Filopodia extending from the processes were found beneath the pia mater. Relocating cells displayed contact relationships between themselves; in the caudal part of the stream, translocating neurons were apposed to each other and fibers of various diameters, and in the rostral area of the stream, many fibers were noted, and corresponded to leading processes of relocating neurons, to which other cell bodies had close contact. From the arrangement of the immature neurons and their processes, it can be inferred that developing fibers act as guidance substrates for the translocation of embryonic pontine neurons.

Animals↗

PubMed1982

Evidence for cross-bridge attachment in relaxed muscle at low ionic strength.

In vitro at low ionic strength (mu = 0.02 M) and 5 degrees C, myosin subfragment-1 shows significant binding to regulated actin in the presence of ATP, independent of the concentration of free Ca2+. Under the same conditions, single skinned rabbit psoas muscle fibers develop force only in the presence of Ca2+ and are relaxed in its absence. However, the stiffness, measured with very rapid stretches (0.5% of muscle length in 0.1 ms), is high even when the fibers are relaxed. This "rapid stiffness" of the resting muscle is sensitive to ionic strength, becoming small at normal ionic strength (mu = 0.17 M). At low ionic strength, the rapid stiffness is approximately proportional to the overlap between the actin and myosin filaments. At zero overlap (sarcomere length = 3.8 microns), the stiffness is less than 20% of the value measured at full overlap. This remaining 20% is relatively insensitive to ionic strength, like the passive resting tension, and it may in fact be due to the structures responsible for the resting tension. Thus, both in vitro binding and the effect of overlap on rapid stiffness measurements in fibers suggest that cross-bridges are attached to actin in relaxed muscle at low ionic strength.

Actins↗

PubMed1996

Development of myocardial fiber organization in the rat heart.

Confocal laser-scanning microscopy of phalloidine-stained actin fibers is a relatively new tool for studying the development of myocardial fiber organization. It seems to show orientation of myocytes in rather early embryonic stages. To further evaluate the differentiation of the myocardium, this technique was compared with transmission electron microscopy in rat embryos aged between 11 and 18 days. Although the confocal images of actin filament patterns pointed to early myocyte orientation, the electron micrographs revealed that even at 17 days the ventricular myocardium was far from mature. Myofibrils never completely filled the myocytes, and lack of organization was the rule rather than the exception. The organized structure as revealed by confocal microscopy was based on cell-to-cell continuity, whereas electron microscopy showed crossing and disarray within individual myocytes. Exceptions were in the ventricular trabeculations, which showed precocious myofiber differentiation. The trabeculations probably support ventricular systole in those stages in which the free walls do not yet provide efficient contractions. The other exception was the wall of the outflow tract, which showed well-oriented myofibrils from early stages onwards. Apparently, the outflow tract has a different function in these stages. The differences found between confocal microscopy and electron microscopy suggest that some caution is indicated in the interpretation of fluorescent images of relatively low magnification.

Actins↗

PubMed1975

Sustained decreased in coronary blood flow and excitation of cardiac sensory fibers following sympathetic stimulation.

The effect of electrical stimulation of the efferent cardiac sympathetic nerves on activity of afferent cardiac fibers in the sympathetic nerves and coronary hemodynamics of anesthetized dogs has been examined. During partial constriction of the coronary artery, a brief stimulation of the efferent cardiac sympathetic nerves resulted in sustained excitation of the afferent fibers and a sustained decrease in blood flow of the constricted artery which were associated with systolic bulge of the left ventricle and elevation of the ST segment of electrocardiogram. These changes were not produced without constriction. Pretreatment with phentolamine suppressed excitation of the afferent fibers, development of systolic bulge and elevation of the ST segment. Also, the decrease in coronary blood flow induced by stimulation was replaced by an increase after the administration of the agent. Propranolol suppressed excitation of the fibers, systolic bulge and elevation of the ST segment, but could not eliminate the decrease in blood flow. The results indicate that sympathetic stimulation caused a decrease in coronary blood flow through excitation of the alpha-adrenergic receptors while increasing cardiac work load and energy requirements through excitation of the beta-adrenergic receptors, leading to more severe myocardial ischemia and excitation of the afferent fibers.

Action Potentials↗

PubMed1993

Development of descending fibers to the rat embryonic spinal cord.

Onset and development of descending pathways to the rat embryonic spinal cord was examined by the use of retrograde transport of horseradish peroxidase (HRP). HRP was injected in the lower thoracic segments of the spinal cord of embryos ranging in age from embryonic day (E)14.5 to E20.5. A small number of labelled cells were found in the brain stem nuclei on E14.5: they were located in medullary as well as pontine reticular formation, lateral vestibular nucleus and interstitial nucleus of the medial longitudinal fasciculus. By E15.5 labelled cells were observed in the reticular formation of the caudal part of the medulla oblongata, medullary raphe nuclei, locus coeruleus, subcoeruleus nucleus, Barrington's nucleus and central gray of the midbrain. Cells in the red nucleus and in the nucleus of the solitary tract were labelled by E 16.5 and E17.5, respectively. Thereafter, labelled cells were first found in a few other nuclei: the gracile nucleus on E19.5 and the paraventricular nucleus on E20.5. The present study demonstrated that all the major supraspinal inputs except corticospinal fibers project to the lower thoracic spinal cord by E20.5.

Animals↗

PubMed1988

Immunohistological localization of cell adhesion molecules L1, J1, N-CAM and their common carbohydrate L2 in the embryonic cortex of normal and reeler mice.

The expression of the cell adhesion molecules L1, J1 and N-CAM and their shared carbohydrate L2 was studied in the embryonic cerebral cortex of normal and reeler mutant mice using light and electron microscopic immunocytochemistry. Apart from a general delay in their appearance in the reeler cortex, the 4 antigens were present with a cellular distribution in both genotypes reflecting the anatomical characteristics of normal and mutant phenotypes. The cell surface glycoprotein L1 was exclusively expressed by neurons, particularly axons, but was never detected at sites of neuron-glia contact. L1 was accumulated in the marginal zone and subplate of the normal cortex and in the homologous layers of the reeler cortex. The secreted glycoprotein J1 was found on glia and neurons. Although initially present in regions of fiber outgrowth, J1 became characteristically excluded from the large fiber tracts at later stages. J1 mapped in the marginal zone and subcortical plate of the normal cortex and in the corresponding layers of the mutant cortex. N-CAM had a more ubiquitous distribution and was present in ventricular zones, particularly at early stages, as well as on glia and neurons and large fiber tracts at later developmental stages. The distribution of the L2 epitope was quite similar to that of the J1 molecule but remained present on large fiber tracts, like N-CAM and L1, also at later developmental stages. These comparative observations in normal and reeler mutant mice lend support to previous suggestions that L1, together with N-CAM, may play a role in the aggregation of neuronal cell bodies after migration and in the fasciculation of developing fiber bundles. They also point to a possible function of the extracellular matrix component J1 in the guidance or support of fiber outgrowth in large fiber tracts.

Animals↗

PubMed1984

Induction and termination of triggered activity by pacing in isolated canine Purkinje fibers.

The clinical importance of delayed afterdepolarizations and resultant triggered activity as a cause of cardiac arrhythmias is uncertain. We studied the response of ouabain-induced delayed afterdepolarizations and triggered activity to a pacing protocol similar to those used clinically in an effort to quantify the types of responses to pacing that occur as a result of this arrhythmogenic mechanism. Isolated canine Purkinje fibers were superfused with 2 X 10(7)M ouabain until delayed afterdepolarizations occurred and attained an amplitude of 5 mV at a paced cycle length of 500 msec. We then studied the induction of triggered activity in these fibers by pacing. We found that: (1) As the pacing cycle length decreased, the coupling interval from the last paced beat to the first triggered beat decreased and 83% of fibers developed triggered activity. (2) The coupling interval of the first triggered beat after single (S2) or double (S2S3) premature beats was in part dependent on preceding pacing cycle lengths. S2 pacing induced triggered activity in 39% of fibers, and S2S3 pacing induced triggered activity in 48% of fibers. We then studied the termination of ouabain-induced sustained rhythmic activity by pacing: 89% of sustained rhythmic activity could be terminated by overdrive pacing at a cycle length less than or equal to 300 msec. The coupling interval of the first beat or first delayed afterdepolarization after the termination of overdrive decreased as pacing cycle length decreased. S2 premature beats reset the sustained rhythmic activity and terminated 14% of sustained rhythmic activity. The coupling interval of the first escape beat or delayed afterdepolarization after S2S3 premature beats decreased as the S2S3 interval shortened, and S2S3 terminated 26% of sustained rhythmic activity. Pacing at an S1S1 cycle length of 400 msec followed by an S2 terminated 50% of sustained rhythmic activity; S1S1 at a cycle length of 400 msec followed by S2S3 terminated 85% of sustained rhythmic activity. This quantitative demonstration of the responses of delayed afterdepolarizations, triggered activity, and sustained rhythmic activity to pacing may be useful in differentiating these from other mechanisms for arrhythmias.

Animals↗

PubMed1984

Curare-induced transformation of myosin pattern in developing skeletal muscle fibers.

The effects of neuromuscular block on the pattern of distribution of myosin isozymes in developing skeletal muscle fibers was examined by immunocytochemistry. The homogeneous population of fibers in the anterior latissimus dorsi (ALD) of the 18-day chick embryo was converted by curare to a mosaic of at least two categories of fibers. Normally all fibers in this slow muscle reacted with antibodies against slow myosin (anti-ALD). They also reacted with an antibody specific for the alkali 1 light chain (anti-delta 1) but not the alkali 2 light chain (anti-delta 2) of fast myosin. After treatment with curare, which inhibits neuronal cell death and increases the number of axonal endings, ALD muscle fibers continued to react with anti-delta 1, but many now reacted with anti-delta 2 as well. The same fibers failed to react with anti-ALD. From this it can be concluded that the myosin in this population was converted to a type not normally present. The changes, therefore, are not merely a result of the preferential loss of a slow type of fiber, nor are they a result of delayed maturation. In contrast, curare had no apparent effect on the fast posterior latissimus dorsi (PLD). As in the normal muscle at 18 days, all fibers reacted strongly with anti-delta 1 and to variable degrees with anti-delta 2, and very few fibers reacted with anti-ALD. Our observations suggest that the dual response to antibodies against fast and slow myosin during development is not a necessary consequence of multiple axon terminals. We present evidence that curare induces the expression of a different myosin in the embryonic ALD, and we suggest that the selective transformation of the fiber population may be a manifestation of a change in composition of the motoneuron pool.

Animals↗

PubMed1984

Relative independence of metabolic enzymes and neuromuscular activity.

Effects of spinal cord transection in 2-wk-old cats on the metabolic, histochemical, and fatigue properties of a fast- and a slow-twitch muscle were determined. Chronic (6-12 mo) spinalization (Sp) resulted in an increased ratio of fast-twitch, oxidative-glycolytic (FOG) to slow-twitch, oxidative (SO) fibers in soleus (SOL). In medial gastrocnemius (MG), Sp produced a histochemical profile suggesting that fast fibers were increased at the expense of slow fibers. Changes in biochemical markers for oxidative (citrate synthase) and glycolytic (GPD) potential were consistent with the histochemical findings. The fatigue index of Sp MG and SOL remained normal and was consistent with the type and degree of fiber type change. Daily treadmill exercise did not markedly alter any of the adaptations. The metabolic and fatigue properties of skeletal muscle of Sp cats are consistent with the view that as some fibers develop "faster-like" characteristics, the oxidative and the glycolytic potential is also enhanced. As was true of the contractile properties and related biochemical data, the changes observed suggest that significant changes occurred within as well as across fiber types. These data, in conjunction with that of chronic EMG recordings, provide evidence that there is a relative independence of both the oxidative potential and the fatigability of a muscle relative to its quantity of activation.

Animals↗

PubMed2006

Normal wound healing in mice deficient for fibulin-5, an elastin binding protein essential for dermal elastic fiber assembly.

Extracellular matrix proteins play a critical role in dermal wound healing by mediating matrix-cell interactions and re-establishing the dermal architecture and environment. Fibulin-5 is an elastin-binding protein essential for elastic fiber development in vivo, and it has recently been shown to inhibit angiogenesis in vitro. Here, we use mice deficient for the fibulin-5 gene (fbln5) to examine the role of fibulin-5 and the effect of the loss of elastic fibers in dermal wound healing. Fbln5 is upregulated in the granulation tissue 14 days after full-thickness wounding in wild-type mice, before the formation of elastic fibers. Although wounded fbln5(-/-) skin showed enhanced neovascularization compared to the wild-type skin, no difference in the rate of wound closure was observed between mutant and wild-type mice. In addition, a breaking strength test revealed that there was no difference in breaking stress or strain between wild-type and fbln5(-/-) wounded skin. These results suggest that fibulin-5 and elastic fibers are not directly involved in short-term wound healing. Clearly, the long-term effect of the absence of fibulin-5 on the function and integrity of regenerated skin needs to be further addressed.

Animals↗

PubMed1997

Inhaled asbestos fibers induce p53 expression in the rat lung.

Humans and rodents exposed to an aerosol of asbestos fibers develop lung injury that can lead to a fibroproliferative response culminating in excessive scarring and impaired lung function. To define the early events that precede asbestos-induced fibrotic lung disease, rats were exposed to an aerosol of chrysotile asbestos fibers for 5 h. At various times after exposure, the lungs of the asbestos-exposed animals were evaluated immunohistochemically for expression of the p53 tumor suppressor protein, a growth regulatory protein. p53 became detectable by immunostaining at the predicted sites of fiber deposition (the bronchiolar-alveolar duct bifurcations) by 24 h after exposure. The number of cells positive for p53 immunostaining increased to a maximal level at 8 days after exposure, decreased by 14 days and returned to a low basal level at the 30-day time point. Control groups of rats that were unexposed or exposed to an aerosol of iron beads were negative for p53 immunostaining throughout the 30-day assessment period. Simultaneous detection of the proliferating cell nuclear antigen (PCNA) at the sites of fiber deposition in the asbestos-exposed animals agrees with our previous finding that p53 binds and regulates the PCNA promoter.

Administration, Inhalation↗

PubMed1999

Determination and development of the larval muscle pattern in Drosophila melanogaster.

This review describes briefly what is known about the early steps of mesoderm differentiation in the fruitfly Drosophila melanogaster. After a summary of general aspects including mesoderm differentiation, mesoderm cell migration and subdivision of the mesoderm, more detail is given about the specification of muscle progenitor cells, due to their role as the earliest obvious landmarks in muscle fiber development in Drosophila. Particular focus is given to recent results on the role of asymmetric cell division in muscle differentiation. Furthermore a short summary of myoblast fusion is provided.

Animals↗

PubMed2003

The sequence dependence of fiber organization. A comparative molecular dynamics study of the islet amyloid polypeptide segments 22-27 and 22-29.

Amyloid fiber formation and the possible polymorphism of molecular arrangements depend on the polypeptide length and composition. Here, we seek the chemical clues underlying these processes. Our starting point is based on the experimental observation that some short peptide segments are able to develop fibers that are very similar to those of their original parent proteins. We focus our study on the NFGAILSS peptide, derived from the human islet amyloid polypeptide (residues 22-29). This peptide turned out to be a perfect example, illustrating the fact that the amyloid microscopic organization is highly complex, rather than simply involving hydrogen bond formation. Furthermore, obtaining a reliable molecular model has allowed us to analyze the differences between the amyloid structure we have obtained for this peptide and that obtained for the previously studied, two residues shorter, segment (residues 22-27, NFGAIL). This comparative study yields some clues about chemical events that govern the aggregation of proteins into oriented fibers, such as molecular packing between sheets and the degree of interaction specificity. We characterize the important role played by the hydrophobic and aromatic residues in the inter-sheet association and present new approaches toward the understanding of the nature of events that are likely to take place during fibril formation. These include analysis of interaction patterns derived from specific sheet-associated packing.

Amino Acid Sequence↗