Cytoskeletal aspects of assisted fertilization

During mammalian fertilization, the zygotic centrosome organizes a large sperm aster, critical for uniting the male and female pronuclei prior to first mitosis. Fluorescent imaging of inseminated human oocytes has shown that centrosomal defects may result in abnormal microtubule nucleation preventing genomic union, suggesting a novel cause of fertilization failure. Working with rhesus monkey gametes, we have developed a preclinical model for understanding the cell biological basis of intracytoplasmic sperm injection (ICSI). Typically, ICSI results in abnormal nuclear remodeling during sperm decondensation due to the presence of the sperm acrosome and perinuclear theca, structures normally removed at the oolemma during IVF; this is turn causes a delay in the onset of DNA synthesis. These unusual modifications raise concerns that the ICSI procedure itself may result in chromatin damage during DNA decondensation and further highlight the need for a more rigorous assessment of methods of assisted reproduction prior to their global application.