Alexandra M Sänger

Publications of Alexandra M Sänger

• Temperature-dependent modification of muscle precursor cell behaviour is an underlying reason for lasting effects on muscle cellularity and body growth of teleost fish.

  Authors: Peter Steinbacher, Julia Marschallinger, Astrid Obermayer, Alois Neuhofer, Alexandra M Sänger, Walter Stoiber

  The Journal of experimental biology. 06/2011; 214(Pt 11):1791-801.

  Temperature is an important factor influencing teleost muscle growth, including a lasting ('imprinted') influence of embryonic thermal experience throughout all further life. However, little is knownTemperature is an important factor influencing teleost muscle growth, including a lasting ('imprinted') influence of embryonic thermal experience throughout all further life. However, little is known about the cellular processes behind this phenomenon. The study reported here used digital morphometry and immunolabelling for Pax7, myogenin and H3P to quantitatively examine the effects of thermal history on muscle precursor cell (MPC) behaviour and muscle growth in pearlfish (Rutilus meidingeri) until the adult stage. Fish were reared at three different temperatures (8.5, 13 and 16°C) until hatching and subsequently kept under the same (ambient) thermal conditions. Cellularity data were combined with a quantitative analysis of Pax7+ MPCs including those that were mitotically active (Pax7+/H3P+) or had entered differentiation (Pax7+/myogenin+). The results demonstrate that at hatching, body lengths, fast and slow muscle cross-sectional areas and fast fibre numbers are lower in fish reared at 8.5 and 13°C than at 16°C. During the larval period, this situation changes in the 13°C-fish, so that these fish are finally the largest. The observed effects can be related to divergent cellular mechanisms at the MPC level that are initiated in the embryo during the imprinting period. Embryos of 16°C-fish have reduced MPC proliferation but increased differentiation, and thus give rise to larger hatchlings. However, their limited MPC reserves finally lead to smaller adults. By contrast, embryos of 13°C-fish and, to a lesser extent, 8.5°-fish, show enhanced MPC proliferation but reduced differentiation, thus leading to smaller hatchlings but allowing for a larger MPC pool that can be used for enhanced post-hatching growth, finally resulting in larger adults.

• Size- and age-dependent changes in adductor muscle swimming physiology of the scallop Aequipecten opercularis.

  Authors: Eva E R Philipp, Maike Schmidt, Carina Gsottbauer, Alexandra M Sänger, Doris Abele

  The Journal of experimental biology. 09/2008; 211(Pt 15):2492-501.

  The decline of cellular and especially mitochondrial functions with age is, among other causes, held responsible for a decrease in physiological fitness and exercise capacity during lifetime. WeThe decline of cellular and especially mitochondrial functions with age is, among other causes, held responsible for a decrease in physiological fitness and exercise capacity during lifetime. We investigated size- and age-related changes in the physiology of exercising specimens of the short lived swimming scallop Aequipecten opercularis (maximum life span 8 to 10 years) from the Isle of Man, UK. A. opercularis swim mainly to avoid predators, and a decrease in swimming abilities would increase the risk of capture and lower the rates of survival. Bigger (older) individuals were found to have lower mitochondrial volume density and aerobic capacities (citrate synthase activity and adenylates) as well as less anaerobic capacity deduced from the amount of glycogen stored in muscle tissue. Changes in redox potential, tissue pH and the loss of glutathione in the swimming muscle during the exercise were more pronounced in young compared to older individuals. This indicates that older individuals can more effectively stabilize cellular homeostasis during repeated exercise than younger animals but with a possible fitness cost as the change in physiology with age and size might result in a changed escape response behaviour towards predators.

• Cellularity changes in developing red and white fish muscle at different temperatures: simulating natural environmental conditions for a temperate freshwater cyprinid.

  Authors: Walter Stoiber, John R Haslett, Ralf Wenk, Peter Steinbacher, Hans-Peter Gollmann, Alexandra M Sänger

  The Journal of experimental biology. 09/2002; 205(Pt 16):2349-64.

  Muscle cellularity patterns in teleost fish have normally been investigated using animals reared under constant temperature conditions. In the present study, Danube bleak (Chalcalburnus chalcoidesMuscle cellularity patterns in teleost fish have normally been investigated using animals reared under constant temperature conditions. In the present study, Danube bleak (Chalcalburnus chalcoides mento) were reared under two different rising temperature regimes (cold, 12-16 degrees C; warm, 18-20 degrees C) designed to mimic the natural conditions experienced by the fish in temperate freshwater environments. Samples were taken from both groups of animals at intervals during their development. Transverse sections at the level of the anal vent were examined using light and electron microscopy, histochemistry and immunohistochemistry techniques. Total cross-sectional area of red and white muscle, as well as fibre numbers and fibre cross-sectional areas of one epaxial quadrant per specimen, were measured. Analysis of fibre numbers and sizes indicated that white and red myotomal muscles each develop in a different manner. In white muscle, the initial growth phase is dominated by fibre hypertrophy, while the later larval growth phase also includes significant hyperplasia. Red muscle growth is mainly due to hypertrophy within the studied developmental period. The temperature regimes applied in the present study may modify the mechanisms of muscle growth in different ways. For white muscle, pre-hatching hyperplasia (i.e. proliferation of somitic white fibre precursor cells) is reduced under the cold regime whereas post-hatching hyperplasia is not. The inverse is true for white fibre hypertrophy. A similar situation is seen with red muscle except that post-hatching hyperplasia is low and refractory to temperature. Rates of increase in relative amount of red muscle appear to depend not only upon species and temperature but also upon whether the fish have been reared under changing or constant thermal regimes. These findings are discussed in relation to 'landmark' events of early ontogeny (hatching, onset of swimming, start of exogeneous feeding) and to their implications for future accurate interpretation of temperature effects on teleost developmental biology and functional ecology.