Understanding fertilization through intracytoplasmic sperm injection (ICSI)

Abstract

Summary Since the establishment of in vitro fertilization, it became evident that almost half of the couples failed to achieve fertilization and this phenomenon was attributed to a male gamete dysfunction. The adoption of assisted fertilization techniques particularly ICSI has been able to alleviate male factor infertility by granting the consistent ability of a viable spermatozoon to activate an oocyte. Single sperm injection, by pinpointing the beginning of fertilization, has been an invaluable tool in clarifying the different aspects of early fertilization and syngamy. However, even with ICSI some couples fail to fertilize due to ooplasmic dysmaturity in relation to the achieved nuclear maturation marked by the extrusion of the first polar body. More uncommon are cases where the spermatozoa partially or completely lack the specific oocyte activating factor. In this work, we review the most relevant aspects of fertilization and its failure through assisted reproductive technologies. Attempts at diagnosing and treating clinical fertilization failure are described.

Total levels, localization patterns, and proportions of sperm exhibiting phospholipase C zeta are significantly correlated with fertilization rates after intracytoplasmic sperm injection

“…It is well understood that human infertility can be attributed to both male and female factors, and that ICSI is predominantly implemented to treat male factor infertility (2). Although fertilization rates after ICSI routinely exceed 80%, 3%-5% of ICSI cases still encounter fertilization failure (34,35). In addition, although conventional semen analysis provides a general assessment with regard to sperm quality, an excessively large number of infertile patients tend to present a normal spermiogram (36)(37)(38)(39).…”

PLCζ sequence, protein levels, and distribution in human sperm do not correlate with semen characteristics and fertilization rates after ICSI

“…As opposed to most reports of PLCζ in FF, which examine patients with poor sperm parameters in autologous ICSI cycles [20,21,32,33], we considered patients with both normal and abnormal semen analysis and included oocyte donation cycles with donors of proven fertility, minimizing the bias of female factors that are critical in FF [34,35].…”

Expression profile ofPLCζ,PAWP,andTR-KITin association with fertilization potential, embryo development, and pregnancy outcomes in globozoospermic candidates for intra-cytoplasmic sperm injection and artificial oocyte activation

“…SOAF(s) compartmentalize as part of the post-acrosomal sheath of sperm perinuclear theca (PAS-PT) and trigger intracellular Ca 2+ -release upon fusion of spermatozoa/oocyte membranes or insemination of spermatozoa into oocyte (Sutovsky et al 2003). Absence of SOAF(s) in globozoospermic individuals because of absence of acrosome and PAS-PT (Lawrence et al, 1997;Neri et al, 2014) during acrosome biogenesis in these individuals may be considered as one reason for failed fertilization in globozoospermic men. A number of candidates have been proposed as SOAF including PLCf (Saunders et al, 2002;Swann et al, 2006) (a spermspecific phospholipase C), TR-KIT (a truncated form of the KIT receptor) (Sette et al, 1997), PAWP (post-acrosomal sheath WWdomain-binding protein) (Wu et al, 2007a,b;Aarabi et al, 2014a) and citrate synthase (Harada et al, 2007).…”