Atypical decondensation of the sperm nucleus, delayed replication of the male genome, and sex chromosome positioning following intracytoplasmic humansperm injection (ICSI) into golden hamster eggs: Does ICSI itself introduce chromosomal anomalies?

Objective: To examine nuclear decondensation, positioning of sex chromosome s, and the S-phase in human sperm nuclei following intracytoplasmic sperm i njection (ICSI) into hamster eggs. Design: Prospective analysis of hamster eggs and human sperm following ICSI . Setting: Division of Reproductive Sciences, Oregon Health Sciences Universi ty and Oregon Regional Primate Research Center. Patient(s): Fertile donor sperm from a commercial source. Intervention(s): Human sperm were examined by immunofluorescence stain, bro modioxyuridine (BrdU) uptake assay and fluorescence in situ hybridization f ollowing ICSI into hamster eggs. Main Outcome Measure(s): Immunostaining and fluorescence in situ hybridizat ion. Result(s): Decondensation of human sperm nuclei occurred initially in the b asal region,and perinuclear theca of sperm persisted around the condensed a pical region. In some sperm nuclei, following ICSI the sex chromosomes were in the apical region, remaining condensed for longer than in the basal reg ion. S-phase entry of human sperm nuclei following ICSI was delayed compare d to the zona-free hamster egg penetration assay. Conclusion(s): These results force questions about the mechanism of male pr onuclear formation after ICSI and suggested new strategies for understandin g the basis of chromosomal anomalies leading to birth defects as well as co ntinuing improvements in the safety and efficacy of infertility therapies. (Fertil Steril(R) 2000;74; 454-60. (C) 2000 by American Society of Reproduc tive Medicine.).