spermatid-specific linker histone H1-like protein mRNA levels, fertilization ability of human spermatozoa, and quality of preimplantation embryos

Fertilization involves a series of cellular interactions culminating in the fusion of gamete membranes, creating a zygote and then an embryo. During the process of human fertilization in vivo or in conventional in vitro fertilization (IVF), sperm must be capable of undergoing the acrosome reaction, binding to the zona pellucida (ZP), and penetrating the ZP to fuse with the oolema. The key role in this process is played by fertilin β [1-5]. Protamines and histones are the proteins that bind to sperm chromatin and contribute in chromatin remodeling during early spermiogenesis. It has been suggested that these proteins may also participate in successful fertilization and embryo development [6]. Using reverse transcription and real-time quantitative PCR reaction (QR-PCR) methods and zygote and embryo scoring, we compared fertilin β, protamine 1 (PRM1), protamine 2 (PRM2), spermatid-specific linker histone 1 (HILS1) mRNAs levels, in vitro fertilization ability of mature spermatozoa, and quality of embryos obtained from in vitro fertilization (IVF) [7,8]. We found significantly lower contents of fertilin β transcript in spermatozoa from patients in which IVF fertilization failed (p<0.001). We also noticed a correlation between high levels of fertilin β and increased quality of embryos (p<0.05). We observed an increase in PRM1 and PRM2 mRNA levels in spermatozoa obtained from patients with successful in vitro fertilization versus compared to the number of these transcripts isolated from spermatozoa of patients in which in vitro fertilization failed (P<0.001), (P<0.001), respectively. We found direct correlation between PRM1 and PRM2 mRNA levels to the quality of embryos (r=0.31, P=0.012), (r=0.31, P=0.011), respectively. The differences in HILS1 mRNA contents between these two groups were not statistically significant (P>0,05). We did not observe an association between HILS1 transcript contents and quality of embryos (r=0.22, P=0.076). We suggest that fertilin β and protamines contribute not only to successful fertilization, but may have an important impact in development of preimplantation embryos.