Can museum egg specimens be used for proteomic analyses?

BACKGROUND: Mass spectrometry and proteomic analyses have become powerful tools for the analysis of proteins and peptides. Investigation of proteins contained in the various layers of the avian eggshell has focused entirely on domesticated species. It has been widely assumed that this existing research can inform the study of wild bird species despite the fact that the vast majority of the diversity in avian species (~95%) exists outside the Orders to which domestic and poultry species belong. Museum collections offer a potentially valuable source of material for studying composition of wild avian eggshell matrix proteins. We used museum and fresh eggshells of common quails Coturnix coturnix to compare the protein composition of their organic matrices. Four eggs of domestic chickens were analysed simultaneously as a control for comparison to the fresh and museum quail eggs. The determination of the proteins was carried out using enzymatic cleavage followed by high-performance mass spectrometry. RESULTS: We found that some of the expected key eggshell proteins (3 out of 11) were not present in the samples of museum quail egg. These proteins were either entirely absent from the museum eggs or the technique was unable to detect them. There was no pattern in the absent proteins in the sense of protein function or where they are located within the eggshell. CONCLUSION: We conclude it is likely that such studies on museum specimens using a proteomic approach will be limited in coverage of proteins and may, therefore, be misleading.