FIGURE 2.

Current status of fertilization and self-incompatibility system. (A) Schematic representation of artificial self/nonself-fertilization in C. intestinalis. There are several ways to achieve artificial self-fertilization. Removing the VC and treating the VC with acidic seawater or proteases relieves the self-fertilization block. In addition, the inhibition of Ca²⁺ influx in spermatozoa, which is controlled by the external Ca²⁺ concentration, is sufficient to block the self-fertilization signal. (B) Gamete proteins involved in each step of fertilization are illustrated. Ub, ubiquitin; Tast, tunicate astacin-like metalloprotease with thrombospondin-type-1 repeat.