Molecular and Computational Biology, Department of Biological Sciences, University of Southern California, Los Angeles, California, USA.
Centre for Evolutionary Biology, School of Biological Sciences (M092), University of Western Australia, Australia.
Biol Reprod. 2021 Oct 11;105(4):1043-1055. doi: 10.1093/biolre/ioab082.
Studies of fertilization biology often focus on sperm and egg interactions. However, before gametes interact, mammalian sperm must pass through the cumulus layer; in mice, this consists of several thousand cells tightly glued together with hyaluronic acid and other proteins. To better understand the role of cumulus cells and their extracellular matrix, we perform proteomic experiments on cumulus oophorus complexes (COCs) in house mice (Mus musculus), producing over 24,000 mass spectra to identify 711 proteins. Seven proteins known to stabilize hyaluronic acid and the extracellular matrix were especially abundant (using spectral counts as an indirect proxy for abundance). Through comparative evolutionary analyses, we show that three of these evolve rapidly, a classic signature of genes that influence fertilization rate. Some of the selected sites overlap regions of the protein known to impact function. In a follow-up experiment, we compared COCs from females raised in two different social environments. Female mice raised in the presence of multiple males produced COCs that were smaller and more resistant to dissociation by hyaluronidase compared to females raised in the presence of a single male, consistent with a previous study that demonstrated such females produced COCs that were more resistant to fertilization. Although cumulus cells are often thought of as enhancers of fertilization, our evolutionary, proteomic, and experimental investigations implicate their extracellular matrix as a potential mediator of fertilization outcomes.
受精生物学的研究通常集中在精子和卵子的相互作用上。然而，在配子相互作用之前，哺乳动物的精子必须穿过卵丘层；在老鼠中，这由几千个细胞组成，它们通过透明质酸和其他蛋白质紧密地粘在一起。为了更好地理解卵丘细胞及其细胞外基质的作用，我们对小家鼠（Mus musculus）的卵丘-卵母细胞复合体（COC）进行了蛋白质组学实验，产生了超过 24000 个质谱来鉴定 711 种蛋白质。七种已知稳定透明质酸和细胞外基质的蛋白质特别丰富（使用光谱计数作为丰度的间接指标）。通过比较进化分析，我们表明其中三种蛋白质进化迅速，这是影响受精率的基因的典型特征。一些选定的位点与已知影响功能的蛋白质区域重叠。在后续实验中，我们比较了来自两种不同社会环境的雌性产生的 COC。与在单一雄性存在下饲养的雌性相比，在多个雄性存在下饲养的雌性产生的 COC 更小，并且对透明质酸酶的解离更具抵抗力，这与先前的研究一致，该研究表明此类雌性产生的 COC 对受精更具抵抗力。尽管卵丘细胞通常被认为是受精的增强剂，但我们的进化、蛋白质组学和实验研究表明，它们的细胞外基质可能是受精结果的潜在介导者。
