Expression of human oocyte-specific linker histone protein and its incorporation into sperm chromatin during fertilization

ObjectiveTo investigate the expression of oocyte-specific linker histone protein (hH1FOO) in human ovaries and its incorporation into sperm chromatin after intracytoplasmic sperm injection (ICSI).DesignLaboratory study.SettingUniversity hospital.Patient(s)Human ovarian tissues were obtained from patients at oophorectomy. Human oocytes and embryos were obtained from infertile patients undergoing IVF and ICSI.Intervention(s)A polyclonal rabbit antibody targeting the predicted hH1FOO protein was used for immunohistochemical analysis. Western blot analysis and the reverse transcriptase–nested polymerase chain reaction were done to detect hH1FOO in chromatin of germinal vesicle–stage oocytes through to two-cell embryos.Main Outcome Measure(s)The hH1FOO antibody reactivity of oocytes, ovarian tissues, and sperm chromatin after ICSI.Result(s)hH1FOO protein was localized in all oocytes from primordial to Graafian follicles. In unfertilized oocytes after ICSI, the chromatin of injected sperm was condensed without hH1FOO incorporation in 45.5% of oocytes, condensed with hH1FOO incorporation in 9%, and decondensed with hH1FOO incorporation in 45.5%. None of the oocytes contained decondensed sperm chromatin without hHFOO incorporation.Conclusion(s)hH1FOO protein was expressed by human oocytes from primordial follicles to early embryogenesis. Sperm nuclei that were still condensed after ICSI could be separated into two categories by hH1FOO incorporation, which might provide valuable information regarding failed fertilization.