| YOLK PROTEINS AND FREE AMINO ACIDS IN ACIPENSERIFORMES |
| FINN, R.N.(1), Lenhardt, M.(2), Ferrara, A.(3), Isely, J.J.(3), Dean, J.(4) Fyhn, H.J.(1) 1: Department of Zoology, University of Bergen, N-5020 Bergen, Norway. nigel.finn@zoo.uib.no; hans.fyhn@zoo.uib.no; 2: Institute for Biological Research "Sinisa Stankovic", 29 Novembra 142, 11000 Belgrade, Yugoslavia. lenhardt@ibiss.bg.ac.yu; 3: South Carolina Cooperative Fish and Wildlife Research Unit, Clemson University, Clemson, South Carolina 29634-0372, USA. jisely@clemson.edu; 4: Natchitoches National Fish Hatchery, 615 Highway 1, Louisiana 71457, USA. Jan_Dean@fws.gov |
| Acipenseriformes can be found throughout the northern hemisphere in both marine and freshwater environments, although almost all spawn in freshwater. Their origin dates back to the late devonian with modern genera appearing in the Triassic – a time when teleosts first began appearing in the marine fossil record. Like many of the early evolving teleosts, certain Chondrostei undertake legendary spawning migrations back to the freshwater environment in which they originated. The adults evolved osmoregulatory adaptations that permitted their exploratory and eventual habitual excursions to the marine environment, but were bound by the osmotic requirements of their eggs to return to their native freshwater for spawning. Recent studies have shown that the pelagic eggs of marine teleosts hydrolyse high molecular weight yolk proteins (lipovitellins) to generate a large pool of free amino acids (FAA) causing oocyte hydration. We have argued that this is a key adaptation that pre-adapts the embryos for development in the hyperosmotic seawater. We have also found that freshwater salmonids degrade high molecular weight yolk proteins during the endogenous larval phase suggesting a possible heritage for the mechanism now active during the final oocyte maturation of marine teleosts with pelagic eggs. Our research focus concerns the origin of this mechanism, and we conducted this study in order to characterise the situation in representatives of the two living families of Acipenseriformes. The SDS-PAGE shows the presence of a yolk protein at ~110 kD in 3 of the 4 extant sturgeon genera (Acipenseridae: Huso huso, Acipenser ruthenus, Scaphyrhynchus platorhynchus) as well as in the paddlefish (Polyodontidae: Polyodon spathula). Cell water and FAA contents remained low, and no yolk proteolysis occurred during final oocyte maturation. During ontogenesis of the shovelnose sturgeon, however, a substantial hydration was observed particularly during post-hatch development. The filling of the urinary bladder was observed during this period. Although an increase in body FAA content occurred during the growth phase no yolk proteolysis was noted during early development of the shovelnose sturgeon. In conclusion, a 110 kD yolk protein, reminiscent of that in teleost yolk was found in these ancient Acipenseriformes, although no signs of the proteolytic events associated with the oocyte hydration mechanism of marine teleosts were observed.
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