Phosphoinositol Turnover Pathway

Three fertilization articles are summarized below:

A 1993 Molecular Biology of the Cell article showed that fertilized Xenopus zygotes had an increase in IP3 mass after insemination and during first cleavage. Our 1997 Mol. Biol. of the Cell paper compares the increase in DAG levels at fertilization.
A 1994 Developmental Biology article argued that Xenopus sperm may induce an increase in zygote Ca++ by increasing IP3 levels in eggs. Before this paper, there was a question as to whether sperm increased intracellular calcium first, and this increased calcium then stimulated phospholipase C and IP3 production. IP3 would then increase calcium in a positive feedback loop.
Our data suggested that a second model of fertilization is correct: sperm increase phospholipase C to increase IP3 first (calcium is not needed as the first step).
A 1997 Molecular Biology of the Cell article measured DAG, choline and phosphocholine levels at fertilization through cleavage. DAG is produced by PI turnover, but we found evidence suggesting that DAG is largely from phosphocholine breakdown and phospholipase D. The role of lipase D is currently being examined. During first cleavage, DAG decreased. Elevation of DAG was through calcium-independent and dependent paths.
With the data in this paper, we have mostly completed our work of quantifying the changes in the mass of the two major products of PI turnover: IP3 and DAG. We have now recorded their levels from maturation of the oocyte through fertilization and first cleavage. We found much smaller changes in IP3 and DAG during oocyte maturation (see our other papers) than we found during fertilization. First cleavage was associated with intermediate changes in these second messengers.

I would like to thank undergraduate students who were involved in this part of our research program: Ronald Espinoza, Mozhdeh Saffari-Parizi, Allan Kirkwood, Sara Hendricks, Amy Herhahn, Wendy Dickerson, Chris Jaynes, Sally Silva, Patrick Ayres, Laura Whitworth/Langley, Melanie Overlay, Brandt Gillam (many of whom were supported by NSF and UCD Undergraduate Research Opportunities Program grants).