Abnormal DNA methylation in oocytes could be associated with a decrease in reproductive potential in old mice

Area of Science:

• Reproductive biology
• Epigenetics
• Developmental biology

Background:

• Female reproductive potential declines with age.
• Epigenetic alterations, including DNA methylation, are implicated in aging.
• Understanding age-related changes in oocytes is crucial for fertility research.

Purpose of the Study:

• To investigate DNA methylation levels and DNA methyltransferase (Dnmt) expression in aging mouse oocytes and pre-implantation embryos.
• To determine if age-related epigenetic changes correlate with reduced reproductive capacity in aged female mice.

Main Methods:

• Comparison of metaphase II (MII) oocytes and pre-implantation embryos from young (6-8 weeks) and aged (35-40 weeks) female mice.
• Assessment of DNA methylation using fluorescence staining.
• Evaluation of DNA methyltransferase (Dnmt1, Dnmt3a, Dnmt3b, Dnmt3L) protein expression via Western blotting.
• Fertilization of oocytes in vitro and in vivo to assess embryo development.

Main Results:

• Significant decrease in DNA methylation levels in oocytes and pre-implantation embryos from aged mice.
• Reduced expression of Dnmt1, Dnmt3a, Dnmt3b, and Dnmt3L proteins in oocytes of aged mice.
• Lower oocyte cleavage and blastocyst rates, reduced pregnancy rates, and increased stillbirth and fetal malformation rates in aged mice.

Conclusions:

• Decreased expression of DNA methyltransferases (Dnmt) and altered DNA methylation in oocytes and embryos are associated with reduced reproductive potential in aged female mice.
• Epigenetic dysregulation due to aging may be a key factor in female infertility.