Second meiotic spindle integrity requires MEK/MAP kinase activity in mouse eggs.

ERK-type MAP kinase activity is required for normal first meiotic (MI) metaphase spindle dynamics and first polar body formation at the MI/MII transition, and for MII arrest until egg activation. MEK and MAPK, however, remain active until meiosis is completed and pronuclei form, but whether MEK/MAPK activity affects MII spindle function during egg activation has been unknown. Polarized light microscopy revealed that the MII spindle rapidly (within approximately 15 min) lost birefringence upon treatment of the egg with U0126, indicating decreased organization at the molecular level upon MEK inhibition.

Assessing the quality of oocytes derived from in vitro maturation: are we looking under the lamppost?

Oocytes are complex cells comprising many cellular systems, each of which is essential for proper oocyte function. Methods to assess the diverse and critical cellular systems in oocytes derived from in vitro maturation are badly needed.