A Proteome Analysis of the Subcutaneous Gel in Avian Hatchlings

摘要

An appropriate level of water loss from eggs is critical to successful hatching. This water may be lost from the egg by evaporation, but where water loss is suboptimal, it is commonly observed that the hatchlings contain substantial amounts of a subcutaneous gel-like fluid. To characterize this fluid, we have analyzed the proteins that are contained within it. The protein complement comprised a small number of proteins in high concentrations. Proteomics analysis of the constituent proteins identified virtually all of these abundant proteins and confirmed that the subcutaneous gel was very similar in protein composition to plasma. However, the subcutaneous gel was substantially depleted of fibrinogen. It is possible that activation of the final stages of the coagulation process might account for the enhanced viscosity, creating a gel-like material that is relatively immobile in the subcutaneous space. This gel may function as a water volume that is partitioned during embryonic development in order to mitigate the effects of high water content of the egg caused by low mass loss during incubation and in some instances might also function as a water reserve to support the hatchling in the first few hours of life free of the shell. An appropriate level of water loss from eggs is critical to successful hatching. This water may be lost from the egg by evaporation, but where water loss is suboptimal, it is commonly observed that the hatchlings contain substantial amounts of a subcutaneous gel-like fluid. To characterize this fluid, we have analyzed the proteins that are contained within it. The protein complement comprised a small number of proteins in high concentrations. Proteomics analysis of the constituent proteins identified virtually all of these abundant proteins and confirmed that the subcutaneous gel was very similar in protein composition to plasma. However, the subcutaneous gel was substantially depleted of fibrinogen. It is possible that activation of the final stages of the coagulation process might account for the enhanced viscosity, creating a gel-like material that is relatively immobile in the subcutaneous space. This gel may function as a water volume that is partitioned during embryonic development in order to mitigate the effects of high water content of the egg caused by low mass loss during incubation and in some instances might also function as a water reserve to support the hatchling in the first few hours of life free of the shell. An avian egg is a self-contained, sealed system within which the embryo develops. During this process, there is substantial movement of fluid from the yolk and albumen to new fluid spaces in the embryo, including blood plasma, interstitial extracellular space, and eye (1Adolph E.F. Ontogeny of volume regulations in embryonic extracellular fluids..Quart. Rev. Biol. 1967; 42: 1-39Google Scholar). Additionally, some water is added by oxidation of lipid from the yolk. However, the egg also loses water by diffusion through the shell, and it is possible for the egg to either lose too much or too little water to allow hatching. In the domestic fowl, hatching success is optimal when water equivalent to about 12% of the initial egg mass (IEM) 1The abbreviations used are: IEM, initial egg mass; 2DGE, two-dimensional gel electrophoresis; MALDI, matrix-assisted laser desorption/ionization; TOF, time-of-flight; SG, subcutaneous gel. is lost. Losses in excess of 19% IEM cause embryonic dehydration and low hatch rate. At the other extreme, water losses lower than 10% IEM diminish hatching success (2Davis T.A. Shen S.S. Ackerman R.A. Embryonic osmoregulation: Consequences of high and low water loss during incubation of the chicken egg..J. Exp. Zool. 1988; 245: 144-156Google Scholar). When eggs are maintained at high relative humidity to diminish water loss, embryonic development proceeds normally and the water content of the developing embryo is normal. As hatching approaches, the excess fluid not