Ph.D.: 1977, University of Washington
Postdoctoral: John Hopkins University
The average age of first-time mothers in the United States has increased from 24.9 years in 1970 to just over 26 years in 2014 as women postpone childbearing. One consequence of increased maternal age is that increasing numbers of families require Assisted Reproductive Technologies (ARTs) to overcome fertility defects. Egg activation is a critical step in fertilization and the long-term goal of our laboratory has been to define the biochemical mechanisms involved in egg activation by sperm with the ultimate aim of improving the efficiency of ARTs.
The role of PYK2 in "outside-in" signaling at the site of sperm contact
Previously, egg activation in mammals was thought to proceed spontaneously following sperm-egg fusion when a sperm-derived phospholipase C (PLCzeta) is introduced into the egg cytoplasm, where it initiates high amplitude Ca2+ oscillations that are sufficient to activate development. However, we recently demonstrated in mice that sperm-egg binding triggers a novel ‘outside-in' signaling event where the PYK2 protein kinase is recruited to the egg cortex underneath the sperm binding site. This event does not require sperm-egg fusion, and plays an important role in incorporating the sperm into the egg cytoplasm.
These findings demonstrate that the egg is not passive during fertilization, but instead responds to sperm contact through a protein kinase-mediated pathways that induces remodeling events in the cortical actin layer that play a role in sperm incorporation. Our new model is significant because it reveals the importance of sperm-egg cell surface interactions as an aspect of zygote quality that could be negatively impacted by ART procedures that bypass sperm-egg interaction (ICSI). An understanding of the surface proteins that induce PYK2 activation could lead to methods for artificially activating this kinase to replace the signals missing in ICSI-activated oocytes with the aim of increasing zygote quality.
Identification of novel pathways critical for egg activation in mice
Over the last thirty years, laboratories around the world have discovered a number of signal transduction pathways that are activated at fertilization and play important roles in cell cycle resumption and activation of development. However, as technology improves, our lab continues to try new methodologies in hopes of discovering novel signaling events critical to egg activation.
We recently made use of a Kinome Array technique to detect changes in protein kinase abundance and phosphorylation state within mouse eggs at different stages after fertilization. Samples collected during anaphase of the second meiotic division exhibited significant (Z-score ratio > 2) changes in 28 egg proteins which are now being validated by other proteomic methods. The results obtained from other samples collected at early and late pronuclear stages are still being analyzed. Once target proteins are validated, functional studies will be undertaken to determine the role that these proteins play during egg activation and their importance for zygote quality.
Selected Recent Publications
William H. Kinsey, PhD