Myogenic cell cycle duration in Harpagifer species with sub-Antarctic and Antarctic distributions:: evidence for cold compensation

In teleosts, the proliferation of myogenic progenitor cells is required for muscle growth and nuclear turnover. We measured the cell cycle and S-phase duration of myogenic cells in the fast myotomal muscle of two closely related Harpagifer species by cumulative S-phase labelling with 5-bromo-2'-deoxyuridine (BrdU). Harpagifer antarcticus is a stenothermal species from the Antarctic peninsula (experiencing temperatures of -2degreesC to +1degreesC) and Harpagifer bispinis is a eurythermal species from the Beagle Channel, Tierra del Fuego (living at +4degreesC in winter and up to 11degreesC in summer). Specific growth rates in the adult stages studied were not significantly different from zero. Myogenic progenitor cells were identified using an antibody against c-met. Seventy-five percent of the c-met(+ve) cells were in a proliferative state in both species. Cell cycle time was 150h at 5degreesC and 81.3h at 10degreesC in H. bispinis (Q(10)=3.4). Cell cycle duration was 35% shorter in H. antarcticus at 0degreesC (111h) than in H. bispinis at 5degreesC. The predicted cell cycle time for H. bispinis at 0degreesC (based on the Q(10) relationship) was 277h, which was more than double that measured for the Antarctic species at this temperature. The results obtained are compatible with an evolutionary adjustment of cell cycle time for function at low temperature in the Antarctic species.