Striatin-3 is a human autoantigen but it is not associated with the S-phase G2 nuclear antigen (SG2NA) staining pattern

Human autoantibodies have a long history of being valuable reagents to identify and characterize unique subcellular compartments, macromolecular complexes, and their individual components. One such discovery started as a unique cell-cycle related immunofluorescence pattern characterized as autoantibody targets localized in S and G2 phase nuclei of tissue culture cells, which became known as the "SG2NA" (SG2 nuclear antigen). These descriptions were followed by the identification of a calmodulin-binding protein family named 'striatin' that was later identified as three paralogs: Striatin/STRN1, Striatin-3/STRN3/SG2NA, and Striatin-4/STRN4/Zinedin. Many subsequent reports have used the designations SG2NA and striatin interchangeably. This report reviews the history of SG2NA and clarifies that striatin-3 is indeed a target autoantigen of some autoimmune sera, but commercially available striatin-3 antibodies or human sera that react with striatin-3 do not produce a SG2 phase nuclear staining pattern on HEp-2 cells. Hence, future reports should not use anti-SG2NA and anti-striatin interchangeably.