SPATA18 (spermatogenesis associated 18), also known as Mieap or SPETEX1, is a 538 amino acid protein that is thought to play a role in cell differentiation during spermatogenesis, particularly during development from late elongate spematids to mature spermatozoa. Localizing to cytoplasm, SPATA18 is encoded by a gene that maps to human chromosome 4q12. Chromosome 4 represents approximately 6% of the human genome and contains nearly 900 genes.