Structural domains comprising this superfamily share the structure of the Spindlin(Spin)/Ssty family of proteins, first identified for their involvement in gametogenesis. Spindlin is a maternal transcript present in the unfertilised egg and early embryo, and it interacts with the spindle apparatus during oogenesis, suggesting it might also be important for mitosis PMID:9053325. Spindlin also appears to be a target for cell cycle-dependent phosphorylation, so it may play a role in cell cycle regulation during the transition from gamete to embryo PMID:11806826. Ssty is a multi-copy, Y-linked spermatogenesis-specific transcript required for normal spermatogenesis PMID:15020475. It is also thought that Ssty plays an analogous role to spindlin in sperm cells, specifically during the transition from sperm cells to early embryo, and in mitosis.