UC San Diego

PLC-[zeta] is a sperm factor responsible for inducing calcium oscillations inside an oocyte leading to outcomes ranging from oocyte activation, block of polyspermy and down-regulation of genes involved in oocyte development. The ultimate goal of these experiments was to develop a bacterium, S. typhimurium that could mimic the effects of sperm on a mature oocyte. While the development of PLC- [zeta] was underway, another goal was attempted. No one had ever tested the interactions between S. typhimurium and an oocyte, and it was uncertain if the bacterium could adequately deliver proteins into the ooplasm. Although S. typhimurium's secretion and translocation apparatus was tested with HeLa cells using a 1 HeLa to 100 bacteria ratio, and adenylate cyclase (reporter) was detected through relative cAMP levels, several factors posed a problem with the infection of the oocyte. For example, Salmonella's needle was 500 times shorter than the length of the zona pellucida (ZP) of the egg. The zona pellucida, a protein matrix, serves as an additional barrier between the sperm and the egg plasma membrane. Typically, S. typhimurium can bind directly to a host cell and translocate its effector proteins directly into the cytoplasm. In this case, S. typhimurium was only able to penetrate the ZP and secrete into the ooplasm once its numbers reached 1,000,000 cfu per oocyte. With such a high number required to effectively deliver proteins into an oocyte, it was clear that this delivery system was not the ideal alternative to conventional contraceptives