1994 Developmental Biology Article

Sperm Increase Inositol 1,4,5-Trisphosphate Mass in Xenopus laevis Eggs Preinjected with Calcium Buffers or Heparin

Bardley J. Stith, Ronald Espinoza, Dawn Roberts, and Tanya Smart

Dev. Bio. 165, 206-215 (1994)

Abstract:

Although it is known that all fertilization events are due to elevated intracellular calcium, it is not known how sperm induce an increase in zygote intracellular Ca++. We report that sperm can increase inositol 1,4,5-trisphosphate in Xenopus laevis eggs that have been preinjected with calcium buffers to prevent the increase in intracellular Ca++ (both the initial increase and the subsequent wave) after fertilization. After buffering intracellular Ca++ to levels well below basal, IP3 production was not blocked, whereas IP3 metabolism may be inhibited. Also, heparin (an inhibitor of inositol 1,4,5-trisphosphate action and the fertilization response) does not prevent a normal increase in IP3 after fertilization. Conditions that produce various levels of polyspermy are associated with IP3 increases similar to those noted after monospermic fertilization. These data suggest a specific order of fertilization events: sperm utilize an initial production of inositol 1,4,5-trisphosphate to produce the intracellular Ca++ increase at fertilization.