Comparison of the media for isolation and storage of round spermatid nuclei before intracytoplasmic injection

Purpose: This study investigated whether K+-rich medium is better than pure NaCl solution or Na+-rich cell culture medium for handling round spermatid nuclei prior to injection into oocytes (ROSNI). Methods: Round spermatids of the mouse were isolated and stored in isotonic NaCl, a cell culture medium (CZB), or a nucleus isolation medium (NIM) before injection into oocytes. The rates of normal fertilization, embryonic development in vitro, and birth of normal offspring after transfer of embryos to foster mothers were determined Results: In vitro development of ROSNI-produced zygotes to blastocysts was the same when "naked" spermatid nuclei were exposed briefly to three media. However, a long (60-min) exposure of the nuclei to Na+-rich medium was detrimental. In K+-rich NIM "naked" spermatid nuclei best retained their ability to participate in normal embryonic development. Conclusion: NIM was better than Na+-rich medium for retaining isolated spermatids competent to participate in normal embryonic development.