 In mouse and rat, three distinct GPx4 isoforms with different subcellular localization are produced through alternative splicing and transcription initiation; cytosolic GPx4, mitochondrial GPx4 (mGPx4), and nuclear GPx4 (nGPx4).Cytosolic GPx4 has been identified as the only GPx4 isoform being essential for embryonic development and cell survival.The GPx4 isoforms mGPx4 and nGPx4 have been implicated in spermatogenesis and male fertility.