Trace fossils on a Late Ordovician glacially striated pavement in Algeria

An exceptional exposure of Late Ordovician glaciogenic sediments crops out in Dider, SE Algeria, within the Tassili N'Ajjer region. The sediments consist of sandstones and diamictites sandwiched between a Mid Ordovician fluvial and tidal sandstone (In Tahouite Formation) below and Early Silurian shale (Oued Imirhou Formation) above. Stratigraphic discontinuities within the Late Ordovician glaciogene succession include palaeovalley incisions and glacially striated pavements. Striation and fluting of a soft-bedded sediment beneath an ancient ice sheet is supported by abundant dewatering structures and soft-sediment gouges interpreted to have been produced by the action of stone ploughing. In Dider, two types of previously undescribed circular structures sit in negative relief on this glacial pavement, namely 1) paired thumb-shaped impressions 2 cm in diameter and 3 mm in depth, and 2) a 5 cm wide impression with 3 segmented nested cycles. A framboid or aggregate origin may be appropriate for the smaller of the features but the larger impression is interpreted as biogenic: internal complexity is characteristic, discounting concretion moulds and water escape structures. A biogenic origin as a coelenterate resting trace is proposed with speculation on conditions of exceptional preservation in an ancient periglacial environment.     

Avian predation at a Southern Rockhopper Penguin colony on Staten Island,Argentina

We studied predation risk in relation to nest location and subcolony size in Southern Rockhopper Penguins (Eudyptes chrysocome chrysocome) during the chick-rearing period. Striated Caracaras (Phalcoboenus australis), the main predator, preferentially attacked from tussock grasses which are found in the periphery of all subcolonies (peripheral tussocks) and often scattered within them (central tussocks). The greatest numbers of predation and attempted predation events were observed on nests in the periphery of the subcolony next to peripheral tussocks, and on those nests next to central tussocks. Central tussocks offer Striated Caracaras an additional “edge” area from which to prey, much in the same way as do the peripheral tussocks. Predation rate per individual was not correlated with subcolony size possibly due to the presence of central tussocks which, by creating an extra edge area, change the subcolony shape. There is a suggestion (P = 0.06) of increased probability of nest success with subcolony size.     

High resolution radioautographic study of newly formed protein in striated muscle with emphasis on red and white fibres

Summary The elaboration and distribution of newly formed proteins in the striated muscle of 21-day-old mice were investigated by quantitative radioautography at intervals between 2 and 240 min after intravenous injection of tritiated leucine. In radioautographs, the localization and the relative label concentration were comparatively estimated for the different components of mitochondria-rich fibres, in particular of red fibres, from the tibialis anterior muscle and of mitochondria-poor fibres from the oesophageal muscle.As early as 2 min after injection, radioactivity was detected over the nucleus, the polysome-rich sarcoplasm, the A and I bands, the Z lines, and the mitochondria in the two fibre types. Label localization did not change with time. The relative label concentration increased similarly in the polysome-rich sarcoplasm and the A and I bands of both fibre types within 30 min after injection, a confirmation that biosynthesis of myofibrillar proteins takes place rapidly. In each case, concentration was higher in the Z lines than in the I bands, and higher in the I bands than in the A bands, thus showing in vivo that the rates of synthesis of sarcomere protein components are not uniform.However, the relative label concentration was found to be higher in the Z lines of mitochondria-poor fibres than of mitochondria-rich fibres: this suggests that a higher synthetic rate of Z line protein, and probably of actinin, is characteristic of the first type. Inversely, the concentration was higher in the mitochondria of mitochondria-rich fibres. This lead to the belief that high rate of protein synthesis in these organelles may account for the high rate of label incorporation into this type of fibre.The authors wish to thank Miss Françoise Ampeau for her technical assistance in biochemical experiments. Radioautographic techniques were carried out in the Centre de Radioautographie de l'U.E.R. Biomédicale des Saints-Pères Paris, France. This work was supported by grants from Inserm (ATP n 73-441921) and from the Fondation pour la Recherche Médicale Française     

AFM study of the thermotropic behaviour of supported DPPC bilayers with and without the model peptide WALP23

Temperature-controlled Atomic Force Microscopy (TC-AFM) in Contact Mode is used here to directly image the mechanisms by which melting and crystallization of supported, hydrated DPPC bilayers proceed in the presence and absence of the model peptide WALP23. Melting from the gel L_β′ to the liquid-crystalline L_α phase starts at pre-existing line-type packing defects (grain boundaries) in absence of the peptide. The exact transition temperature is shown to be influenced by the magnitude of the force exerted by the AFM probe on the bilayer, but is higher than the main transition temperature of non-supported DPPC vesicles in all cases due to bilayer–substrate interactions. Cooling of the fluid L_α bilayer shows the formation of the line-type defects at the borders between different gel-phase regions that originate from different nuclei. The number of these defects depends directly on the rate of cooling through the transition, as predicted by classical nucleation theory.The presence of the transmembrane, synthetic model peptide WALP23 is known to give rise to heterogeneity in the bilayer as microdomains with a striped appearance are formed in the DPPC bilayer. This striated phase consists of alternating lines of lipids and peptide. It is shown here that melting starts with the peptide-associated lipids in the domains, whose melting temperature is lowered by 0.8–2.0 °C compared to the remaining, peptide-free parts of the bilayer. The stabilization of the fluid phase is ascribed to adaptations of the lipids to the shorter peptide. The lipids not associated with the peptide melt at the same temperature as those in the pure DPPC supported bilayer.     

Observations of satellite cells in rat skeletal muscle incubated in vitro

Summary Satellite cells were studied in the peripheral fibres from isolated rat muscles, which had been incubated for various periods of time. The cells were in an activated state with prominent organelles and increased cytoplasm visible. Mitosis of some satellite cells was occasionally observed. It is suggested that when incubated muscle preparations are used as models for physiological systems in vivo, the state of the satellite cell population should be taken into consideration.     

Species-independent expression of nitric oxide synthase in the sarcolemma region of visceral and somatic striated muscle fibers

The expression and distribution of nitric oxide synthase (NOS) was studied by use of the newly designed specific histochemical NADPH diaphorase staining method and the indirect immunofluorescence technique employing an antiserum to brain NOS in visceral and somatic striated muscles of several mammalian species. Histochemical activity and immunoreactivity were located in the sarcolemma region of type I and II fibers of all muscles investigated. Visceral muscles were more strongly stained than somatic muscles. Furthermore, type II fibers, identified by staining of myosin adenosine triphosphatase activity after pre-incubation at alkaline pH, were more intensely labeled than type I fibers. In addition, NOS activity was detected in the area of the sarcolemma of intrafusal fibers. No obvious differences between species were observed. It was concluded that NOS of striated muscles probably makes up the richest and most important nitric oxide source in mammals.     

Irregular patterns of actin and myosin filaments in human skeletal muscle cells

Summary The ultrastructural study of cross sections of normal skeletal muscle cells showed the existence of irregular patterns of actin filaments in connection with the hexagonal pattern of the myosin filaments. The actin filaments surrounding each myosin filament vary in number from 6 to 11. The most frequent relationship is 9 to 1, followed by 10 to 1 and 8 to 1. The hexagonal pattern of actin filaments was observed only in the 6 to 1 arrays; as the actin filaments increase in number, they tend to form different polygons or circles around the myosin filaments. All described patterns may occur in each sarcomere. The actin to myosin filament ratio varies from 3 to 4 within each individual myofibril. The described variability of the actin filaments arrays leads to several difficulties in an explanation of the mechanism of muscular contraction.Director, Chief of Section, Histology. Profesor Agregado de Embriología e HistologíaProfesor Adjunto de Embriología e HistologíaResidente de Anatomía Patol'ogica de la Ciudad Sanitaria La Paz     

Elektronenmikroskopische Untersuchung der quergestreiften Muskelfasern im Corpus pineale von Wistar-Ratten

Zusammenfassung Unter 35 Pinealdrüsen von erwachsenen Wistar-Ratten wurden 8 mit quergestreiften Muskelfasern gefunden. Diese liegen in der Peripherie des Organs und in der Nähe des Pinealstiels. In 3 Fällen wurden direkte Kontakte zwischen Muskelfasern und Kapillaren gesehen.Die Pinealmuskelfasern besitzen ein Sarkolemma, das aus einer Basalmembran und einem retikulären Fibrillengitter aufgebaut ist. Mehrere Merkmale, die für embryonale Muskelfasern charakteristisch sind, werden in den Pinealmuskelfasern gefunden: Reichtum am Sarkoplasma, Armut an Myofibrillen, helikoidale Polyribosomen, unterschiedlich lokalisierte und häufig longitudinale Triaden, Übergang von granulärem in agranuläres sarkoplasmatisches Retikulum, Anzeichen mikropinozytotischer Prozesse, ungeordnete Myofilamente und primitiv gebaute A-Bänder. Die A- und I-Bänder sind in Längsschnitten gut sichtbar, während H-Zonen und M-Streifen meistens fehlen. Die Z-Streifen, gut ausgebildet nach jeder Fixation, sind nie reglemäßig und geradlinig wie in der Skelettmuskulatur. Die Länge einer Sarkomere beträgt 1,25–1,4 m nach OsO₄-Fixation und 2,4–3,1 m nach Aldehydvorfixation. Soweit elektronenmikroskopische Befunde ein Urteil erlauben, dürften die Pinealmuskelfasern — obwohl embryonalen Charakters — kontraktionsfähig sein.In einem Fall wurde ein wahrscheinlich (neuro)endokrino-muskulärer Kontakt zwischen einer Muskelfaser und einem Pinealzellausläufer gefunden.

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Electron microscopic investigation of the striated muscle fibers in the pineal body of wistar rats

Summary 8 of 35 pineal bodies obtained from adult male Wistar rats were found to contain striated muscle fibers. These are located at the periphery of the pineal body or in close proximity to the pineal stalk. In 3 cases a direct contact between capillaries and muscle fibers was observed.The pineal muscle fibers possess a sarcolemma which is formed by the basal membrane and a network of reticular fibers. Several features characteristic of embryonic muscle fibers are found in the fibers of the pineal body: abundance of sarcoplasm, scarce myofibrils, helicoidal polyribosomes, triads variously located and frequently longitudinally oriented, transition of rough- to smooth-surfaced endoplasmic reticulum, presence of micropinocytotic vesicles and primitively formed A-bands. A- and I-bands are well visible in longitudinal sections, while H- and M-bands are mostly lacking. The Z-lines, well formed after every fixation, are never regular and straight as seen in skeletal muscles. After fixation in OsO₄ the length of a sarcomere is 1,25–1,4 m, after aldehyde prefixation it is 2,4–3,1 m. According to electron microscopic findings the pineal muscle fibers, although being of embryonic character, seem to have the ability to contract.In one case a possibly (neuro)endocrino-muscular contact between a muscle fiber and a pineal cell process has been observed.

     

Satellite cells of striated muscle after compression injury so slight as not to cause degeneration of the muscle fibres

Summary Electron microscopy of musculus bulbi rectus superior in the rat reveales increase in the number of. muscle satellite cells during the first 10–12 hours following compression injury so slight as not to cause degeneration of the muscle fibre. These satellite cells are situated close to the muscle nuclei and, in contrast to those in the intact rectus superior, they have a pale nucleus with a conspicuous nucleolus, sparse, pale cytoplasm containing a few small mitochondria, a mainly agranular endoplasmic reticulum and numbers of pinocytotic vesicles along their cell membrane. Later on, between 24 and 48 hours, the cytoplasm increases greatly in amount and extendes in long processess over a considerable length of the muscle fibre. An increase in the number of mitochondria and free ribosomes, the appearance of polysomes and great numbers of Golgi complexes and a decrease in the number of pinocytotic vesicles is noted. On the 4th day, some of the satellite cells have still further extended their cytoplasm beneath the muscle basement membrane, while others are apposed to the muscle fibre only with a minor part of their membrane. On the 9th day, only satellite cells comparable in number and structure with those in intact muscles are found.The possibility is discussed that the increase and subsequent decrease in the number of these satellite cells as well as the changes in their morphology at different periods after the injury reflect morphogenesis of satellite cells originating from the nuclei of the muscle fibre by mitotic division even after a trauma, too slight to cause any visible muscle injury. The observations are interpreted as giving new support to the hypothesis that muscle satellite cells may be of importance in posttraumatic muscle regeneration.