DEVELOPMENTAL COMPETENCE OF IN-VIVO AND IN-VITRO MATURED PORCINE OOCYTES AFTER SUBZONAL SPERM INJECTION

In vivo and in vitro matured porcine oocytes were fertilized by subzon al sperm injection (SUZI), and their subsequent development in vitro w as examined to determine whether ooplasmic incompetence is the major c ause of limited developmental ability of in vitro matured/ fertilized porcine oocytes (Experiment 1). There was no significant difference in rates of fertilization (61% vs. 70%), monospermy (37% vs. 45%), and m ale pronuclear formation (77% vs. 61%) between in vivo and in vitro ma tured oocytes. Blastocyst formation rate was significantly lower for i n vitro matured oocytes (11% vs. 42%; P < 0.001). Forty-six percent of in vivo matured oocytes cleaved to the 2-4-cell stage by 24 hr in cul ture after SUZI, compared with 3% of in vitro matured oocytes (P < 0.0 1). In experiment 2, in vitro development of in vitro matured oocytes with evenly and unevenly granulated cytoplasm were compared after SUZI to examine whether developmentally competent in vitro matured oocytes can be identified on the basis of morphological appearance. Most of t he blastocysts obtained developed from oocytes with unevenly granulate d cytoplasm (7/56 vs. 1/45; P > 0.05). Experiment 3 revealed that the proportion of oocytes with evenly granulated cytoplasm was originally low (11%) in the population of oocytes used for in vitro maturation, a nd it increased approximately 3-fold (36%; P< 0.001) after maturation. These results suggest that ooplasmic incompetence in porcine in vitro matured oocytes is the major cause of their limited developmental com petence. Cytoplasmic maturation measured by male pronucleus formation does not directly reflect developmental competence of the oocytes. It was also shown that evenness of granulation of the cytoplasm is not a useful morphological indicator of developmental competence. (C) 1996 W iley-Liss, Inc.