Gamete Biology

Aged Mouse Oocytes Fail to Readjust Intracellular Adenosine Triphosphates at Fertilization

Abstract
Postovulatory aging of oocytes significantly affects embryonic development. Also, altered Ca²⁺ oscillations pattern can be observed in fertilized aged mouse oocytes. Because Ca²⁺ oscillations depend on Ca²⁺ release and reuptake in the endoplasmic reticulum, and the latter relies upon ATP availability, we simultaneously measured changes in intracellular ATP concentration ([ATP]_i) and Ca²⁺ oscillations in the fresh and aged mouse oocytes. We continuously assessed changes in [ATP]_i from intracellular free Mg²⁺ concentration measured by fluorescent dye Magnesium Green (MgG) while intracellular Ca²⁺ concentration ([Ca²⁺]_i) was monitored by Fura-PE3. At fertilization, MgG fluorescence was transiently increased concomitant with the first transient elevation of [Ca²⁺]_i indicating a relative decrease in [ATP]_i. In the fresh oocyte, it was quickly followed by a significant decrease below the baseline indicating a relative increase in [ATP]_i. In contrast, in the aged oocytes, such a decrease in MgG fluorescence was not observed. In the separate experiment, ATP content in the fresh and aged oocytes was determined in vitro by the luciferin-luciferase assay. Intracellular ATP contents measured in vitro were comparable in the unfertilized fresh and aged oocytes. Intracellular ATP content at 5 hrs after fertilization was increased in the both oocytes, where the fresh oocyte showed a significantly higher intracellular value than the aged oocyte. These findings suggest that aged mouse oocytes fail to readjust the level of intracellular ATP at fertilization. Relative deficiencies of ATP at fertilization might lead to the altered Ca²⁺ oscillations pattern and poor developmental potency commonly noted in the aged oocyte.

Key words: Aging • Calcium • Developmental biology • Fertilization

This article has been cited by other articles:

				I. Segers, T. Adriaenssens, W. Coucke, R. Cortvrindt, and J. Smitz Timing of Nuclear Maturation and Postovulatory Aging in Oocytes of In Vitro-Grown Mouse Follicles with or Without Oil Overlay Biol Reprod, May 1, 2008; 78(5): 859 - 868. [Abstract] [Full Text] [PDF]

				K. T. Jones Meiosis in oocytes: predisposition to aneuploidy and its increased incidence with age Hum. Reprod. Update, March 1, 2008; 14(2): 143 - 158. [Abstract] [Full Text] [PDF]

				M. T. Johnson, E. A. Freeman, D. K. Gardner, and P. A. Hunt Oxidative Metabolism of Pyruvate Is Required for Meiotic Maturation of Murine Oocytes In Vivo Biol Reprod, July 1, 2007; 77(1): 2 - 8. [Abstract] [Full Text] [PDF]

				V.J. Hall, D. Compton, P. Stojkovic, M. Nesbitt, M. Herbert, A. Murdoch, and M. Stojkovic Developmental competence of human in vitro aged oocytes as host cells for nuclear transfer Hum. Reprod., January 1, 2007; 22(1): 52 - 62. [Abstract] [Full Text] [PDF]