Expression and immunolocalization of the calpain-calpastatin system in the human oocyte

Objective: To investigate the expression of the calpain-calpastatin system in the human oocyte. Design: The expression of the calpain-calpastatin system was determined by immunohistochemistry and immunoblot analysis. Setting: Academic research laboratory. Patient(s): Twenty Israeli women who underwent IVF for fertility problems. Intervention(s): Oocytes that had no pronuclei 24 hours after insemination by either conventional IVF or intracytoplasmic sperm injection were retrieved for the study. Main Outcome Measure(s): Analysis of calpain isoforms (m, μ) and calpastatin distribution within the human oocyte. Result(s): Western blot analysis confirmed the expression of calpain and calpastatin. Immunohistochemistry of fixed, permeabilized oocytes exhibited localization of both calpains to the cortical region of the oocyte, as well as the cytosol. Calpastatin seemed to be distributed throughout the cytosol, with a marked accumulation in the cell membrane. We have demonstrated a negative correlation between the occurrence of cortical granule exocytosis and the stability of the metaphase plate. Conclusion(s): A complete calpain-calpastatin system is expressed in the human oocyte and might play a role in the various calcium-mediated processes occurring during activation of human oocytes.