Migration of myogenic cells in the rat extensor digitorum longus muscle studied with a split autograft model

Summary The ability of myogenic cells to migrate perpendicular to the long axis of freely autografted muscles was examined. Rat extensor digitorum longus muscles were divided, and one half was devitalized by repeated freezing in liquid nitrogen while the other half was kept viable in physiologic saline. The halves were reunited with sutures and grafted back into the original muscle bed. At intervals between 5 and 25 days the grafts were removed and examined histologically for the presence of myotubes within the devitalized region. Myotubes were first seen in the devitalized half 10 days postgrafting with the maximum number of myotubes observed after 12 to 15 days. These results indicate that myogenic cells are capable of migration perpendicular to the long axis of the muscle fibers in an autograft.     

Filamin structure,function and mechanics: are altered filamin-mediated force responses associated with human disease?

The cytoskeleton framework is essential not only for cell structure and stability but also for dynamic processes such as cell migration, division and differentiation. The F-actin cytoskeleton is mechanically stabilised and regulated by various actin-binding proteins, one family of which are the filamins that cross-link F-actin into networks that greatly alter the elastic properties of the cytoskeleton. Filamins also interact with cell membrane-associated extracellular matrix receptors and intracellular signalling proteins providing a potential mechanism for cells to sense their external environment by linking these signalling systems. The stiffness of the external matrix to which cells are attached is an important environmental variable for cellular behaviour. In order for a cell to probe matrix stiffness, a mechanosensing mechanism functioning via alteration of protein structure and/or binding events in response to external tension is required. Current structural, mechanical, biochemical and human disease-associated evidence suggests filamins are good candidates for a role in mechanosensing.     

Embryonic origin of skeletal muscle cells in the iris of the duck and quail

Summary The origin of skeletal muscle cells in avian iris muscle was investigated by quantitative analysis of heterochromatin profiles at the electron-microscopic level in irides of six types of quail-duck chimeras. Each of the following tissues was transplanted into the head region from quail to duck between stages 9 and 10: cranial neural crest; trunk neural crest; midbrain and adjacent mesoderm; forebrain; forebrain without neural crest; and forebrain without neural crest and mesoderm. The average ratio of heterochromatin profile to nucleus profile in iris skeletal muscle cells was high (quail type) in the dorsal iris, but low (duck type) in the ventral iris of the chimeras resulting from isotopic transplantation of cranial neural crest. Heterotopic transplantation of trunk neural crest to cranial position resulted in failure of development of skeletal muscle cells in the dorsal iris, but not in the appearance of skeletal muscle cells in the ventral iris. The average ratio of heterochromatin profile to nucleus profile in iris skeletal muscle cells was high in the chimeras resulting from transplantation of midbrain region and the chimeras resulting from transplantation of forebrain region, intermediate in the chimeras resulting from transplantation of forebrain region without neural crest, and low in the chimeras resulting from transplantation of forebrain region without neural crest and mesoderm. These results indicate that the skeletal muscle cells in the dorsal iris are of cranial neural crest origin while those in the ventral iris are not, and could possibly arise from cranial mesoderm.     

Activation of caspase-9 and its influencing factors in beef during conditioning

To study the activation of caspase-9 and its potential influence in conditioning, longissimus thoracis (LT), semitendinosus (STN) and psoas minor (PMi) muscles were used to analyze the ratio of pro-apoptotic bax to anti-apoptotic bcl-2 in fresh tissues and observe the changes in ATP, cytosolic cytochrome c and caspase-9 activity levels during storage at 4°C. Caspase-9 activity at 5 h is higher than the activity at 0 and 24 h in the muscles (P<0.001). The ATP content decreased between 0 and 3 h, between 8 and 14 h in the PMi and LT muscles (P<0.0001), whereas between 0 and 5 h, between 8 and 14 h in the STN muscle (P<0.0001). There is 60.2%, 55.3% and 43.1% available ATP in the STN, LT and PMi muscles at 5 h, respectively. The cytosolic cytochrome c level increased during 5 and 24 h storage in the LT and PMi muscles (P<0.0001), during 5 and 96 h in the STN muscle (P<0.0001). The cytosolic cytochrome c at 24 h (P<0.001) and ratio of bax to bcl-2 (P<0.05) was higher in the PMi than in other muscles. We concluded that the increase in cytosolic cytochrome c and available intracellular ATP should be responsible for the increase in caspase-9 activity; the activation of caspase-9 could be limited by the subsequent depletion of ATP; the postmortem release level of cytochrome c could be determined by the ratio of bax to bcl-2 in fresh tissues.     

Development of the hand and wrist bones in chimpanzees

Skeletal developmental of chimpanzees was studied cross-sectionally. By application of the TW2 method, we described the skeletal development of chimpanzees and compared their skeletal development with humans'. A development pattern of chimpanzees repeated accelerations and decelerations displaying “early-juvenile trough,” “pre-adolescent peak,” “mid-adolescent trough,” and “post-adolescent peak” in incremental curves. Sex differences in skeletal development are slower development in males during infant and early juvenile phases, and greater increment around the adolescent phase in males. Females are fully mature at younger ages than males, e.g. about one and a half years. In comparison with chimpanzees, humans have such characteristics as a longer slower period of juvenile development and a shorter spurt-like adolescent fast period which ends with full maturity.     

Aging leads to inferior Achilles tendon mechanics and altered ankle function in rodents

Spontaneous rupture of the Achilles tendon is increasingly common in the middle aged population. However, the cause for the particularly high incidence of injury in this age group is not well understood. Therefore, the objective of this study was to identify age-specific differences in the Achilles tendon-muscle complex using an animal model. Functional measures were performed in vivo and tissues were harvested following euthanasia for mechanical, structural, and histological analysis from young, middle aged, and old rats. Numerous alterations in tendon properties were detected across age groups, including inferior material properties (maximum stress, modulus) with increasing age. Differences in function were also observed, as older animals exhibited increased ankle joint passive stiffness and decreased propulsion force during locomotion. Macroscale differences in tendon organization were not observed, although cell density and nuclear shape did vary between age groups. Muscle fiber size and type distribution were not notably affected by age, indicating that other factors may be more responsible for age-specific Achilles tendon rupture rates. This study improves our understanding of the role of aging in Achilles tendon biomechanics and ankle function, and helps provide a potential explanation for the disparate incidence of Achilles tendon ruptures in varying age groups.     

The skeletal biology of the Virginia Indians

Statistical analysis of one eastern and two western Virginia Indian skeletal samples reveals a general association between geographical and biological distance. However, the data suggest the importance of gene flow as a factor in minimizing local microdifferentiation. Females appear to contribute a disproportionate share to gene flow. This may be attributed to the widespread and apparently frequent practice of acquiring females and children through capture during recurring warfare.     

Chemical and physical methods in dating human skeletal remains

Chemical and physical methods for dating skeletal remains were examined. Benzidine reaction, ultra-violet fluorescence, specific gravity and supersonic conductivity were carried out on 71 dated skeletal findings distributed over the span of the last 3,500 years. Results given by benzidine reaction and ultra-violet fluorescence basically coincide, and positive readings were obtained up to about 200–350 years. Values measured in specific gravity and supersonic conductivity testing show a parallel trend, pointing out a clear difference between samples of the three first centuries and the ones belonging to more ancient periods examined.     

Effects of wing-pad removal and corpus allatum implantation on development of wings, flight muscles, and related structures in the striped ground cricket, Allonemobius fasciatus

ABSTRACT. Removal of a hindwing pad from late instar nymphs of the striped ground cricket, Allonemobius fasciatus DeGeer (Gryllidae) inhibits the formation of long-winged adults. All nymphs become short-winged when their hindwing pad is removed during the sixth (penultimate) instar or during the first 2 days of the seventh instar. When a hindwing pad is removed on day 4 of the seventh instar or later, there is no effect on wing development and at least 50% of the crickets emerge as long-winged adults as in controls.
The period sensitive for removal of a hindwing pad varies among different structures, e.g. elytra, hindwings, flight muscles, and the acrotergite of the first abdominal segment. As a result, some intermediate forms are produced when a hindwing pad is removed in the middle of the seventh instar.
Implantation of corpora allata (CA) into late instar nymphs also inhibits formation of long-winged adults. When CA are implanted on day 2 or 3 of the seventh instar, some of the resulting adults have abnormally short elytra. Implantation of CA at an earlier stage produces supernumerary (eighth instar) nymphs.