Sperm penetration at the maturing metaphase I stage can trigger oocyte activation in a mouse model

Area of Science:

• Reproductive Biology
• Developmental Biology
• Assisted Reproductive Technology

Background:

• Conventional in vitro fertilization (IVF) typically uses metaphase II (MII) oocytes.
• The developmental potential of maturing metaphase I (MI) oocytes following IVF is less understood.
• Investigating alternative oocyte sources could expand options in assisted reproduction.

Purpose of the Study:

• To determine if spermatozoa can penetrate maturing MI oocytes.
• To evaluate the subsequent development of oocytes fertilized at the MI stage using conventional IVF.
• To assess the viability and chromosomal integrity of embryos derived from MI oocytes.

Main Methods:

• ICR mice were utilized for oocyte collection at different time points post-HCG injection.
• Maturing MI oocytes (7h post-HCG) and MII oocytes (15h post-HCG) were subjected to conventional IVF.
• Developmental parameters including fertilization, cleavage, blastocyst formation, and live birth rates were assessed.
• Chromosomal number and DNA methylation status were analyzed.

Main Results:

• Spermatozoa successfully penetrated maturing MI oocytes, triggering activation.
• A significant proportion of embryos from fertilized MI oocytes reached the blastocyst stage.
• Despite developmental potential, a substantial number of these embryos were triploid due to the absence of the second meiotic division.
• Live births were achieved from some embryos derived from MI oocytes.

Conclusions:

• Maturing MI oocytes can be fertilized via conventional IVF and possess developmental potential.
• Healthy offspring can be produced from maturing MI oocytes, indicating their potential as a biomaterial source in assisted reproduction.
• The high incidence of aneuploidy in embryos derived from MI oocytes warrants further investigation, particularly regarding implications for human IVF.