Academic Staff

The ability to distinguish self from non-self is a fundamental property of life, underpinning processes such as immunity and reproduction. Fertilization, however, represents a striking exception: sperm and egg from different individuals undergo selective cell–cell fusion, a process that requires highly specific molecular recognition. Despite its central importance, the underlying mechanisms remain poorly understood across many animals, including mammals. Here, we use the marine chordate ascidian as a model to dissect this process. As simultaneous hermaphrodites, ascidians possess a robust self-incompatibility system that prevents self-fertilization at the molecular level. Eggs reject self-derived sperm while permitting fusion with non-self sperm, providing a uniquely tractable system in which selective acceptance during fertilization is clearly manifested. By leveraging this system, we aim to uncover the evolutionary origins and general principles governing self–non-self discrimination and the exceptional permissiveness of cell fusion in fertilization.