Cellular and molecular events after in vitro fertilization and intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) has heralded an era of tremendous i mprovements in treating male infertility leading to the births of thousands of babies. However, recent concerns over possible long-term effects of ICS I on offspring has prompted the development of a preclinical, nonhuman prim ate model to assess the safety of ICSI. Fluorescent imaging of rhesus macaq ue IVF zygotes revealed that this species shares many similarities with hum ans in terms of cytoskeletal and chromatin dynamics during fertilization. H owever, rhesus monkey zygotes fertilized by ICSI resulted in abnormal nucle ar remodeling leading to asynchronous chromatin decondensation in the apica l region of the sperm head, delaying the onset of DNA synthesis. The persis tence of the acrosome and perinuclear theca on the apex of sperm introduced into the oocyte by ICSI may constrict the DNA in this region. Despite thes e differences, normal rhesus monkey ICSI embryos have been produced and hav e lead to several births after transfer. The irregularities described in th is paper raise concerns that the ICSI procedure may result in chromatin dam age during DNA decondensation and further highlight the need for devising i mproved pre-clinical assessment prior to global acceptance of this, and oth er, novel methods of assisted reproduction. (C) 1999 by Elsevier Science In c.