Essential for spermiogenesis. Interacts with PACRG. Several isoforms have been identified differing in their 5'-untranslated exons. These isoforms show different tissue expression. Some are expressed in various tissues, including lung, liver, brain, testis, oviduct and oocytes. Some are testis-specific. Detected as early as 6 days after birth and up-regulated during spermatogenesis. Mice are viable, but males are sterile, producing only a few sperm that are morphologically abnormal. Spermatogenesis is dramatically impaired at the stage of elongation and condensation. Spermatozoa exhibit failure of flagellar formation, disorganization of sperm axonemes and deformed heads. Belongs to the MEIG1 family.