Stage-specific expression of lanosterol 14[alpha]-demethylase in mouse oocytes in relation to fertilization and embryo development competence

Asian - Australasian Journal of Animal Sciences, March, 2009 by Xiaoming Song, Hong Ouyang, Ping Tai, Xiufen Chen, Baoshan Xu, Jun Yan, Guoliang Xia, Meijia Zhang

AY9944 can specifically inhibit activities of the sterol [DELTA]14-reductase and .7-reductase to decrease the transform of T-MAS from FF-MAS (Kim et al., 1995), which leads to the accumulation of FF-MAS in mouse CEOs (Leonardsen et al., 2000). In our results, similar to the positive control, more than 80% of fertilization oocytes in 5 [micro]M AY9944 pre-cultured group developed into blastocysts (Figure 4). However, blastocyst development in groups pre-cultured were significantly lower with 0, 25 or 50 [micro]M AY9944. Meanwhile, the oocytes degeneration after in vitro fertilization among all AY9944 pre-culture groups was dose-dependently increased (data not shown). Previous studies have shown that addition of AY-9944 to rat follicle-enclosed oocytes (FEOs) in culture increased FF-MAS within 8 h of culture and caused the resumption of meiosis, and further extension of the culture period led to an increase in the number of degenerating oocytes (Cao et al., 2004). As an inhibitor of cholesterol biosynthesis, high concentration of AY9944 caused the oocyte degeneration. This result indicates that cholesterol is necessary for oocytes to mature and get full fertilization and early embryos development competence, since high concentration of AY9944 may inhibit the production of cholesterol deeply.

Improvement of outcome after in vitro fertilization is a constant challenge. The introduction of new stimulation protocols and drugs may increase the proportion of mature oocytes, fertilization, and cleavage rates together with better early embryo quality and thereby higher implantation rates. Previous studies have shown that addition of FF-MAS to culture medium had a positive effect on the cytoplasmic and nuclear maturation of the oocytes (Hegele-Hartung et al., 1999; Donnay et al., 2004). We compared the cell numbers among azalanstat or AY9944 pre-cultured oocytes derived blastocysts with normal in vivo developed blastocysts. In 5 [micro]M AY9944 pre-cultured oocytes derived blastocysts, the total cell number was similar to the control group in which collected CEOs were inseminated directly without any pre-culture, and the ICM/total ratio was more similar to the in vivo developed blastocysts. However, the blastocysts derived from 25 [micro]M azalanstat pre-cultured oocytes has a significant low total cell number and more abnormal ICM/total ratio than in vivo developed blastocysts. The results show that possible accumulation of FF-MAS in mouse CEOs by a proper concentration of AY9944 pre culture may increase blastocyst development and improve embryo quality in cell number level.

In summary, our results suggest that LDM may have a positive effect on the oocyte plasma maturation for fertilization and early embryo development in mouse, the possible mechanism of this event remain to be established.

ACKNOWLEDGMENTS

We thank Dr. M. R. Waterman (Vanderbilt University, Nashville, USA) for LDM antibody; Dr. D. C. Swinney (Roche Bioscience, Palo Alto, CA, USA) for azalanstat (RS-21607); and Weyth-Ayerst (Princeton, NJ, USA) for AY9944.