Dr. Sutovsky's research has implicated the ubiquitin-proteasome pathway in the control of mitochondrial inheritance after mammalian fertilization and in the proteolytic mechanism for the sperm quality control during spermatogenesis. The central hypothesis of this research is that the maturation and function of human and animal spermatozoa is guided by the ubiquitin system in the testis, epididymis, and during/after fertilization. The components of the ubiquitin system in the spermatozoon are compartmentalized and developmentally regulated. The respective ubiquitin-dependent machineries regulate spatially and temporally separated events during the sperm cell life, such as sperm production in the testis, sperm maturation in the epididymis, penetration of the egg coat, zona pellucida during fertilization, targeted degradation of the paternal mitochondria, harboring paternal mitochondrial genes inside the fertilized egg.