Molecular heterogeneity of urinary proteins in wild house mouse populations

Major urinary proteins (MUPs) from the urine of individual wild mice were characterized using electrospray ionization mass spectrometry (ESI-MS) and compared to MUPs from the urine of inbred mice. The wild mice showed considerable variation between individuals in the expression of a group of MUPs with similar masses. Some individuals excreted MUPs of unique molecular mass whilst some failed to express MUPs seen commonly in the other individuals. All the wild individuals contained proteins not previously observed in inbred mice. Urine from one individual was fractionated using anion exchange chromatography prior to analysis by ESI-MS. By analysing urine from inbred samples under the same conditions it was possible to relate, using mass and net charge in solution, MUPs from the wild sample to the MUPs that have been observed previously in inbred strains. This has allowed tentative identification of some MUPs from the wild mouse. The effect of collection history of urine from wild mice was also investigated. ESI-MS analysis of MUPs in a faecally contaminated sample showed the loss of a C-terminal tripeptide when compared to an uncontaminated sample from the same mouse, consistent with the presence of a specific endopeptidase. Similarly a sample of pooled urine provided by twelve individuals trapped from the same population showed evidence of loss of the C-terminal dipeptide.