The first focus of our laboratory addresses molecules and physiological mechanisms involved in fertilization and early development.
An example of this first focus is our study of the mechanisms of sperm motility initiation in Pacific herring from the San Francisco Bay estuary and the egg-derived ligand that signals the intracellular ionic changes and subsequent motility initiation (Drs. Carol Vines, Fred Griffin, and Ed Smith). These sperm have evolved a unique mode of motility initiation in that they surprisingly remain immotile in the environment for hours until they contact an egg, at which time an extracellular glycoprotein stimulates an ionic cascade resulting in flagellar motion. These ionic events are dependent on lowered salinity (in particular Na+) that is typical in the winter months in the estuary.
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Male herring spawn first depositing large quantities of immotile sperm in the water. This is often called “white water”. These sperm can fertilize eggs for at least 24hrs. after release in the water.
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In collaboration with colleagues in Japan and University of Hawaii we have found that sperm motility initiation, successful fertilization, embryo development, and even larval survival and growth are dependent on the lowered salinities that occur in normal years in the estuary. We are collaborating with colleagues in Japan to investigate both the basic ionic signaling events in sperm motility initiation as well as differences in salinity tolerance of herring populations along the Pacific Rim. We are also studying the impacts of suspended SF Bay sediments on development of herring. Even low concentrations of clean sediments can impact normal larvae if eggs are exposed within 2 hrs of spawning; exposure at later time of development does not impact larval morphology. In addition to research on non-mammalian systems, we have been investigating the role of DEFB126, a beta-defensin that coats the mammalian sperm surface and “cloaks” sperm from being attacked by the female reproductive tract immune system (Ted Tollner, Ph.D. candidate). This glycoprotein is part of the innate immune system and is related to immuno-protective peptides used by invertebrates.
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Figure, right: Herring sperm undergo an increase in intracellular calcium when they initiate motility upon exposure to the egg-derived molecule, SMIF. Calcium increase is detected here using the calcium probe Fluo-3 and the scanning laser confocal microscope. |
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| Figure, above: Herring eggs exposed to suspended SF Bay sediments within 2 hrs. of spawning, bind sediments and retain them throughout development. |
Figure, above: Larvae that hatch from eggs with attached sediments show serious abnormalities. This occurs down to 125 mg/L of sediments in water. |
