SUBZONAL FERTILIZATION OF MOUSE ROUND SPERMATIDS

Mouse round spermatids were electrofused with homologous mature oocyte s to examine the behaviour of their nuclei within the ooplasm and the abilities of development. A single spermatid was injected in the periv itelline space of a mature oocyte and an electron fusion pulse was giv en. The best round spermatid-oocyte pairs (RS-O) fusion took place at 20-30 s AC (1 MHz; 50 V/cm) followed by a single fusion DC pulse (3 70 0-3 800 V/cm, 25 mu s) and another 30 s AC current. The total survival rate and fusion rate of RS-O were 89.0% (575/646) and 61.9% (356/575) , respectively. 49.2% (175/356) of fused oocytes developed to 2PN stag e. The concentration of Ca2+ in the fusion medium produced no signific ant effect on the above targets. The 2PN development rate of the fused RS-O from the oocytes collected 14-16 h after hCG injection was highe r than others. 32.6% (57/175) of the 2PN oocytes had fully developed s permatid (male) and oocyte (female) pronuclei. The rest spermatid-deri ved pronuclei remained small, in size throughout the pronuclear stage. 192 fertilized eggs were transferred surgically into the oviducts of the pseudopregnant female mouse. 12 offspring were produced.