5.8 Thursday, Jan. 3 Intracellular diffusion constraints may influence organelle distribution in skeletal muscle HARDY, KM*; DILLAMAN, RM; KINSEY, ST; University of North Carolina Wilmington; University of North Carolina Wilmington; University of North Carolina Wilmington firstname.lastname@example.org
Different organelles require different conditions to function inside of a cell. Mitochondria depend on oxygen flux, and produce small, rapidly diffusing metabolites that must travel to sites of use in the cell. Further, mitochondria undergo division and breakdown, allowing distribution to change over time. Nuclei, however, do not require oxygen, and they produce slower moving macromolecules that must also diffuse across the cell. The differing properties of organelles affects their cellular distribution. In organisms that undergo large developmental increases in cell size, these molecular transport requirements become increasingly important. In the blue crab, Callinectes sapidus, swimming muscle fibers undergo extreme ontogenetic hypertrophy. Using confocal microscopy we found that anaerobic light fibers respond to increased growth by redistributing their mitochondria to the fiber periphery where oxygen flux is high, rather than maintaining mitochondria homogenously scattered throughout the cell, as is the case in juveniles. This leads to longer diffusion distances, but small metabolite diffusion is fast enough to largely offset these increases. Aerobic dark fibers evolved intricate subdivisions, leading to short diffusion paths for all size classes. Throughout maturation, mitochondria are found both at the periphery and in the core of these subdivisions. Conversely, the independence of nuclei from oxygen freed them to be distributed across the entire large light fibers, thus minimizing the distance over which mRNA and proteins travel. This is in contrast to most skeletal muscle nuclei, and those of the dark fibers, which are found primarily at the fiber edge. Since nuclear distribution is not flexible in skeletal muscle, the small light fibers of juveniles exhibit the same pattern.