Myosatellite cells in muscle of growing carp (Cyprinus carpio L.)

Myosatellite cells are small spindle shaped myogenic cells situated between the sarcolemma and the basal lamina that surrounds every muscle fibre. Based on information from mammals and birds, myosatellite cells are considered to play an important role in postlarval muscle growth in fish. Myosatellite cells are not only thought to provide the extra nuclei needed in the outgrowth of already existing muscle fibres (hypertrophy) but are also thought to provide new additional fibres (hyperplasia). The investigations described in this thesis showed that although the percentage of muscle nuclei that are myosatellite nuclei decreased with increasing length of the fish, the total number of myosatellite cells present in white axial muscle of carp remained about the same. However, the total number of myosatellite cells was so low, that it is very improbable that these cells are the only source of the additional muscle nuclei in hypertrophy. We developed a method to isolate and culture myosatellite cells from axial muscle of carp. Our in vitro studies showed that isolated carp myosatellite cells can differentiate into myotubes. These studies also showed that the population of myosatellite cells contains subpopulations that differ in their differentiational stage. The relative size of these experimentally defined subpopulations changed with increasing length of the fish. In young carp of about 5 cm standard length, muscle growth probably depends mainly on postmitotic myogenic cells that are formed in an earlier stage of growth. The correlation of the changes in the relative size of the subpopulations of myosatellite cells with the decrease in the occurrence of hyperplasia indicates that hyperplasia and hypertrophy are dependent on separate populations of myogenic cells. To prove this theory, markers that enable the identification of these cells will have to be found. We used isolated carp myosatellite cells as an antigen to produce monoclonal antibodies against markers specific for (subpopulations of) these cells. Such antibodies would also enable the (immuno- histochemical) lightmicroscopical identification of myosatellite cells in situ. The criteria for the in situ identification of these cells now still necessitates the use of transmission electron- microscopy. However, non of the antibodies we produced reacted with myosatellite cells only. In future investigations, the use of molecular biological techniques (eg. probes against genes of the MyoD family) probably will be of great use to increase our knowledge of the regulation of muscle growth in fish. This knowledge is not only important in comparative biology, but can also be of advantage in the field of fish-farming as justified optimisation of processes requires its thorough knowledge.