Initial steps on mapping differentially expressed proteins in bovine preantral follicles and ovarian tissue: An approach using single-follicle MALDI-MS and mass spectrometry imaging (MSI) analysis

The molecular mechanisms regulating follicular development and ensuring primordial follicle activation remain undefined. To help elucidate these mechanisms, this proteomic study of bovine ovarian tissue identified the differential molecular profiles of preantral follicles together with the spatial distribution of the most abundant molecular components in the tissue. Isolated primordial, primary and secondary follicles were individually placed on a MALDI target plate for mass spectral acquisitions, with detection of different m/z ranges. Ovarian tissue was sectioned and analysed in the m/z 400-2,000 range. Results of the first analysis indicated a similarity pattern in the molecular protein profile among different follicular classes in the m/z ranges of 100-1000 and 25,000-200,000, but in the m/z ranges of 800-4000, 4000-20,000 and 15,000-70,000, primary and secondary follicles shared similar clustering profiles which were different from primordial follicles (p < .05). In the second analysis, it was possible to correlate some intense molecular components in the tissue from global mass spectrum with the ions detected in the first analysis. Molecular components at m/z 11,325 (+/- 230) were also detected in primary and secondary follicles in the experiment with isolated follicles, in addition to ions at m/z 4,029 (+/- 120), 13,799 (+/- 70), 5,547 (+/- 9), 15,313 (+/- 200), 7,018 (+/- 40) and 7,663 (+/- 90) which were also intensely detected in primary and secondary follicles. The present proteomic approaches evaluated different mass ranges of preantral follicles in bovine ovarian tissue and also indicated the spatial distribution of the most abundant molecular components. This study hopes to pave the way for future research identifying and characterizing specific proteins involved in follicle activation in bovine follicles, in order to better understand folliculogenesis and potentially improve mammalian follicle culture systems.