SPATA1, a novel cell-surface protein, is involved in shaping the sperm head during spermatogenesis. SPATA1 is localized at chromosome 1q21. At least three isoforms of SPATA1 are known to exist. The longest is preferentially expressed in hematopoietic tissues. Its extracellular domain contains a single immunoglobulin-like domain, and its intracellular segment has two immunoreceptor tyrosine-based inhibition motifs (ITIMs). It is thought to have an important role in hematopoietic cell signaling. The mid-sized isoform contains a short intracellular part without ITIMs, while the shortest isoform lacks the transmembrane segment and represents a potential soluble protein (2, 3).