Mammalian fertilization, IVF, ICSI: physiological/molecular parameters, clinical application

Fertilization is associated with several phenomena: rearrangement of euplastic cytoskeleton, intra-cellular communication, cellular polarity, and the release of a variety of complex systems. Several criteria are used to score fertilization. On the day after fertilization, oocytes are cleaned of cumulus and examined for presence of 2 pronuclei and any possible cytological anomalies. Function tests to evaluate fertilization include SPA, ZBA, SCSA, AAA acrosome reaction and fluorescent probes. Fertilization failure, silent polyspermy, aster arrest, mitotic arrest, aster growth defect, or immuno-logical mechanisms cause infertility. Sperm-induced oocyte activation may be due to ligand-recep-tor-mediated interaction or a soluble sperm-derived factor that enters the oocyte at the time of fusion. Any abnormalities in transcription, translation, or any other significant molecular process responsible for producing the oocyte-activating ligand/effector molecule during spermatogenesis and/or spermatogenesis will ultimately cause fertilization failure. The centrosome is paternally derived. During the time course of fertilization the sperm centrosome is orchestrating producer mobilization, syngamy and, ultimately, early cleavage. Vesicle-associated membrane protein(VAMP) is typically lost at cell surface during sperm penetration. Understanding cytoskeletal motility during fertilization requires sophisticated digital imaging including conventional epifluorescence microscopy, laser scanning confocal microscopy and time lapse video microscopy. Clinical application of the recent finding is discussed with emphasis on timing of coitus or insemination, to coincide with time of monitored ovulation. Future research directions are outlined.