The proteasome inhibitor MG-132 induces maturation delay and aneuploidy in mouse oocytes

Abstract

Objective: To test the hypothesis that temporal perturbations during oocyte maturation (OM) predispose mammalian oocytes to abnormal chromosome segregation.Design: A controlled, dose-response, in vitro study utilizing the potent, reversible, cell-permeable proteasome inhibitor MG-132 (carbobenzoxy-L-leucyl-L-leucyl-leucinal)and mouse oocytes.Materials/Methods: Outbred, ICR mice were given PMSG 46h prior to collecting and culturing follicular oocytes in media containing 0, 5.0, 7.5, and 10.0 mcg/ml MG-132 for 6h. Oocytes were then rinsed and further cultured for 17h in MG-132-free media. Oocytes were processed and analyzed for numerical and structual chromosome aberrations.Results: Transient inhibition of proteasome-mediated proteolysis during mouse OM in vitro resulted in dose-response delays during OM and higher levels of aneuploidy. Oocytes exposed to MG-132 exhibited greater delays during metaphase I (MI) as demonstrated by significantly (p <0.01) higher frequencies of MI oocytes and lower frequencies of premature centromere separation. Furthermore, the frequencies of metaphase II oocytes displaying single, unpaired chromatids and aneuploidy significantly (p <0.01) increased with MG-132 dose.Conclusions: These findings suggest that the MG-132-induced transient delay of proteasomal activity during mouse OM in vitro predisposed oocytes to abnormal chromosome segregation. Although these data support the hypothesis tested, additional data are needed to further investigate the roles of proteasome-mediated proteolysis and other potential molecular mechanisms of aneuploidy during OM.Supported by: Department of Obstetrics & Gynecology, Louisiana State University Health Sciences Center, Shreveport, LA, USA. Objective: To test the hypothesis that temporal perturbations during oocyte maturation (OM) predispose mammalian oocytes to abnormal chromosome segregation. Design: A controlled, dose-response, in vitro study utilizing the potent, reversible, cell-permeable proteasome inhibitor MG-132 (carbobenzoxy-L-leucyl-L-leucyl-leucinal)and mouse oocytes. Materials/Methods: Outbred, ICR mice were given PMSG 46h prior to collecting and culturing follicular oocytes in media containing 0, 5.0, 7.5, and 10.0 mcg/ml MG-132 for 6h. Oocytes were then rinsed and further cultured for 17h in MG-132-free media. Oocytes were processed and analyzed for numerical and structual chromosome aberrations. Results: Transient inhibition of proteasome-mediated proteolysis during mouse OM in vitro resulted in dose-response delays during OM and higher levels of aneuploidy. Oocytes exposed to MG-132 exhibited greater delays during metaphase I (MI) as demonstrated by significantly (p <0.01) higher frequencies of MI oocytes and lower frequencies of premature centromere separation. Furthermore, the frequencies of metaphase II oocytes displaying single, unpaired chromatids and aneuploidy significantly (p <0.01) increased with MG-132 dose. Conclusions: These findings suggest that the MG-132-induced transient delay of proteasomal activity during mouse OM in vitro predisposed oocytes to abnormal chromosome segregation. Although these data support the hypothesis tested, additional data are needed to further investigate the roles of proteasome-mediated proteolysis and other potential molecular mechanisms of aneuploidy during OM. Supported by: Department of Obstetrics & Gynecology, Louisiana State University Health Sciences Center, Shreveport, LA, USA.