Determination of the effect of repeated superovulation on telomerase expression and telomere length in mouse oocytes

Objective: To determine the effects of repeated superovulation on the Tert and Terc genes expression and telomere length in mouse germinal vesicle (GV) and metaphase II (MII) oocytes. Method: Four groups from Balb/C female mice consisting of control (C; n=12), one time superovulated (1S; n=12), three times with one week intervals (3S; n=12); five times with one week intervals (5S; n=12) were created, and GV and MII oocytes were obtained from these groups. The expression levels of the Tert and Terc genes by RT-qPCR, TERT protein level by immunofluorescence staining, and telomere length by qPCR were determined. The obtained data were analysed by one-way ANOVA and post-hoc Tukey test. Results: The Terc gene expression level in GV oocytes from 5S group was higher than 1S group (P<0.05). Terc level in MII oocytes from 5S group was higher than C group (P<0.05). The Tert mRNA level increased in GV oocytes obtained from 1S and 5S groups than C group (P<0.05). TERT protein was detected as densely in the nucleus and in the cytoplasm of GV oocytes; densely localized in the cytoplasm and polar body of MII oocytes. It is worth noting that TERT level in MII oocytes gradually increased from 1S to 5S groups (P<0.01). Telomere length in GV oocytes of 1S, 3S and 5S groups were shorter than C group (P<0.001). Telomere length in MII oocytes obtained from C and 3S groups was shorter than those of 1S and 5S groups (P<0.001). Conclusion: Repeated superovulation changes the telomerase components, Tert and Terc genes expression, TERT protein level, and telomere length in GV and MII oocytes. These changes may be associated with some developmental disorders, which are observed in the oocytes as a result of assisted reproductive techniques. Key Words: repeated superovulation, telomerase expression, telomere length, oocytes, mouse