SPIN1 (spindlin 1), also known as SPIN or ovarian cancer-related protein (OCR), is a 262 amino acid nuclear protein suggested to play a role in regulation of the cell-cycle during the transition from gamete to embryo. A member of the SPIN/STSY family, SPIN1 localizes to interphase nucleus and mitotic chromosomes, and is modified by phosphorylation in a cell-cycle-dependent fashion. A meiotic spindle-binding protein, SPIN1 overexpression has been shown to cause defects in mitotic spindles, thereby resulting in chromosome instability and potential tumorigenesis.