HAC stability in murine cells is influenced by nuclear localization and chromatin organization

Background  

Human artificial chromosomes (HAC) are small functional extrachromosomal elements, which segregate correctly during each cell division. In human cells, they are mitotically stable, however when the HAC are transferred to murine cells they show an increased and variable rate of loss. In some cell lines the HAC are lost over a short period of time, while in others the HAC become stable without acquiring murine DNA.     

Na v1.4 and Na v1.5 are modulated differently during muscle immobilization and contractile phenotype conversion

Muscle immobilization leads to modification in its fast/slow contractile phenotype. Since the properties of voltage-gated sodium channels (Na(v)) are different between "fast" and "slow" muscles, we studied the effects of immobilization on the contractile properties and the Na(v) of rat peroneus longus (PL). The distal tendon of PL was cut and fixed to the adjacent bone at neutral muscle length. After 4 or 8 wk of immobilization, the contractile and the Na(v) properties were studied and compared with muscles from control animals (Student's t-test). After 4 wk of immobilization, PL showed a faster phenotype with a rightward shift of the force-frequency curve and a decrease in both the Burke's index of fatigability and the tetanus-to-twitch ratio. These parameters showed opposite changes between 4 and 8 wk of immobilization. The maximal sodium current in 4-wk immobilized fibers was higher compared with that of control fibers (11.5 ± 1.2 vs. 7.8 ± 0.8 nA, P = 0.008), with partial recovery to the control values in 8-wk immobilized fibers (8.6 ± 0.7 nA, P = 0.48). In the presence of tetrodotoxin, the maximal residual sodium current decreased continuously throughout immobilization. Using the Western blot analysis, Na(v)1.4 expression showed a transient increase in 4-wk muscle, whereas Na(v)1.5 expression decreased during immobilization. Our results indicate that a muscle immobilized at optimal functional length with the preservation of neural inputs exhibits a transient fast phenotype conversion. Na(v)1.4 expression and current are related to the contractile phenotype variation.     

Effects of adrenaline on the isolated heart of the trout (Salmo gairdneri R.) before and after transfer from fresh water to sea water

1. Adrenaline induces positive inotropic and chronotropic effects on the isolated heart of the trout (Salmo gairdnerii) via the stimulation of beta adrenoreceptors. 2. The effects are relatively more marked in winter than in spring. But there is no seasonal variation as in the cel. The intrinsic reactivity of the heart is not basically modified after a transfer from fresh water to sea water. 3. However, after such a transfer, adrenaline induces an increase of the membrane resting potential which suggests that adrenaline can enhance the activity of the Na/K pump and/or modify the Ca/K balance and could improve the cardiac performances during the "crisis period" following the transfer.     

Sodium Channel NaV1.5 Expression is Enhanced in Cultured Adult Rat Skeletal Muscle Fibers

This study analyzes changes in the distribution, electrophysiological properties, and proteic composition of voltage-gated sodium channels (Na_V) in cultured adult rat skeletal muscle fibers. Patch clamp and molecular biology techniques were carried out in flexor digitorum brevis (FDB) adult rat skeletal muscle fibers maintained in vitro after cell dissociation with collagenase. After 4 days of culture, an increase of the Na_V1.5 channel type was observed. This was confirmed by an increase in TTX-resistant channels and by Western blot test. These channels exhibited increased activation time constant (τ_m) and reduced conductance, similar to what has been observed in denervated muscles in vivo, where the density of Na_V1.5 was increasing progressively after denervation. By real-time polymerase chain reaction, we found that the expression of β subunits was also modified, but only after 7 days of culture: increase in β₁ without β₄ modifications. β₁ subunit is known to induce a negative shift of the inactivation curve, thus reducing current amplitude and duration. At day 7, τ_h was back to normal and τ_m still increased, in agreement with a decrease in sodium current and conductance at day 4 and normalization at day 7. Our model is a useful tool to study the effects of denervation in adult muscle fibers in vitro and the expression of sodium channels. Our data evidenced an increase in Na_V1.5 channels and the involvement of β subunits in the regulation of sodium current and fiber excitability.     

Cultivation of primmorphs from the marine sponge Suberites domuncula: morphogenetic potential of silicon and iron

Marine demosponges (phylum Porifera) are rich sources for potent bioactive compounds. With the establishment of the primmorph system from sponges, especially from Suberites domuncula, the technology to cultivate sponge cells in vitro improved considerably. This progress was possible after the elucidation that sponges are provided with characteristic metazoan cell adhesion receptors and extracellular matrix molecules which allow their cells a positioning in a complex organization pattern. This review summarizes recent data on the cultivation of sponges in aquaria and--with main emphasis--of primmorphs in vitro. It is outlined that silicon and Fe(+++) contribute substantially to the formation of larger primmorphs (size of 10 mm) as well as of a canal system in primmorphs; canals are probably required for an improved oxygen and food supply. We conclude that the primmorph system will facilitate a sustainable use of sponges in the production of bioactive compounds; it may furthermore allow new and hitherto not feasible insights into basic questions on the origin of Metazoa.     

Myasthenia gravis and asymptomatic monoclonal gammapathy. Detection of autoantibody activity of the monoclonal immunoglobulin

Simultaneous occurrence of "myasthenia gravis" and monoclonal "asymptomatic" gammapathy has been observed in a 83 years old patient. Antistriated muscle antibodies could be detected at a level of 1/1,000 but no antiacetylcholine receptors antibodies. The antibody activity is located both in the monoclonal IgG kappa and in the polyclonal IgG. This case illustrates the frequent occurrence of several auto-immune disorders in a same patient.     

Maturation by LctT is required for biosynthesis of full-length lantibiotic lacticin 481

In lantibiotic lacticin 481 biosynthesis, LctT cleaves the precursor peptide and exports mature lantibiotic. Matrix-assisted laser desorption ionization-time of flight mass spectrometry revealed that a truncated form of lacticin 481 is produced in the absence of LctT or after cleavage site inactivation. Production of truncated lacticin 481 is 4-fold less efficient, and its specific activity is about 10-fold lower.