Inactivation of histone H1 kinase by Ca2+ in rabbit oocytes

✍ Scribed by Philippe Collas; Thomas Chang; Charles Long; James M. Robl

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 649 KB
• Volume: 40
• Category: Article
• ISSN: 1040-452X
• DOI: 10.1002/mrd.1080400215

✦ Synopsis

Abstract

The present study investigated the role of intracellular Ca^2+^ (Ca^2+^~i~) elevation on the inactivation of maturation promoting factor (MPF) in rabbit oocytes. The effects of the number of Ca^2+^ stimulations and of the amplitude of Ca^2+^~i~ elevation on the profile of histone H1 kinase activity were determined. A Ca^2+^ stimulation consisted of transferring mature oocytes from culture medium to 0.3 M mannitol containing 0.1–1.0 mM CaCl~2~, and pulsing them at 1.25 kV/cm for 10 μsec, or microinjecting 2–8 mM CaCl~2~ into the oocyte cytoplasm. The number of electrically‐induced Ca^2+^ stimulations was varied, and amplitude of the Ca^2+^~i~ rise was controlled by altering Ca^2+^ concentration in the pulsing medium or the injection pipette. Ca^2+^~i~ concentration was determined with fura‐2 dextran; oocytes were snap‐frozen at indicated time points and assayed for H1 kinase activity. The activity was quantified by densitometry and expressed as a fraction of activity in nonstimulated oocytes. Electrically‐mediated Ca^2+^~i~ rises inactivated H1 kinase in a manner dependent on the number of Ca^2+^ stimulations. A single Ca^2+^ stimulation inactivated H1 kinase to 30–40% of its initial activity. However, H1 kinase inactivation was only transient, regardless of the amplitude of the electrically‐ or injection‐mediated Ca^2+^~i~ elevation. Increasing the number of Ca^2+^ stimulations helped to maintain H1 kinase activity at basal (pronuclear) levels. The results show the necessity of a threshold of Ca^2+^~i~ concentration to trigger MPF inactivation, and suggest a role for the extended period of time over which Ca^2+^~i~ oscillates at fertilization. © 1995 Wiley‐Liss, Inc.