Is the mouse a clinically relevant model for human fertilization failures?

This study compares failed fertilization oocytes from patients participatin g in an in-vitro fertilization (IVF) programme with failed fertilization oo cytes from B6SJLF(1)/ J mice, in order to characterize and describe the dis tribution of DNA in oocytes that do not undergo normal fertilization. Our g oal is to evaluate the mouse IVF system as a model to gain insight into rea sons for human fertilization failures. All oocytes were stained with the vi tal fluorescent dye, Hoechst 33342, which rapidly stains double-stranded DN A. Of the 237 human oocytes that had been scored as failed fertilization by brightfield microscopy, 61 (25.7%) showed the presence of at least one spe rmatozoon within the oocyte cytoplasm, In contrast, out of 69 failed fertil ization mouse oocytes, only one oocyte showed the presence of a spermatozoo n within its cytoplasm, Mouse failed fertilization oocytes exhibited a sign ificantly lower internal sperm rate (P < 0.0001) than human failed fertiliz ation oocytes, Human failed fertilization oocytes show a higher incidence o f sperm penetration, but the cytoplasm fails to support pronuclear developm ent, whereas, at least in this strain, mouse failed fertilization oocytes a rise from an inability of the spermatozoa to penetrate the oocyte, This stu dy suggests that the mouse is not a clinically relevant model for human fer tilization failures.