Archive for April, 2007
Stability of Membrane Associated Alpha-L-Fucosidase in Human Sperm Cells
Two novel isoforms of alpha-L-fucosidase are present in human semen. Our lab has recently shown alpha-L-fucosidase is cryptically held within the acrosomal compartment and enriched within the sperm equatorial segment. Increase in enzyme activity is apparent following permeabilization of the sperm plasma membrane. The occurrence of these novel isoforms is provocative. Sperm proteins potentially involved in sperm-egg interactions must maintain their functional integrity as they travel through the female reproductive tract. The goal of this project was to investigate the stability of membrane associated alpha-L-fucosidase in human sperm. Seminal plasma and Percoll washed sperm cell populations were incubated for 72 hours at 37C, 5% CO2, 100% humidity. At various times during prolonged incubation, sperm cells were permeabilized with 0.01% TritonX-100 and enzyme assays using the fluorogenic substrate 4-MU-fuc were performed to measure enzyme activity. Stability of seminal plasma and membrane associated alpha-L-fucosidase was determined. Seminal plasma alpha-L-fucosidase activity rapidly decreased within 24 hours incubation at 37C, 5% CO2, 100% humidity. Conversely, alpha-L-fucosidase activity from Percoll washed cell populations persisted up to 72 hours incubation under the same conditions. Seminal plasma alpha-L-fucosidase is considerably less stable than the membrane associated isoform. Control assays containing 4-MU-fuc and HSM or 0.01% TritonX-100 did not interfere with measurement of alpha-L-fucosidase activity. Data from these experiments support the notions that 1) membrane associated alpha-L-fucosidase is stable for extended periods of time, consistent with a possible role in sperm-egg interaction and 2) compartmentalization within the human sperm is key to preserving protein integrity.
Causes and consequences of population decline in an endangered pupfish, Cyprinodon bovinus
When intrasexual interactions influence reproductive success, declines in population size may alter individual reproductive success as well as the breeding system of the species. The endangered Leon Springs pupfish, Cyprinodon bovinus, has a breeding system where large males defend territories around female oviposition sites, while smaller males show satellite or sneaker tactics to gain matings. In related species, absence of territorial males results in satellites taking over territorial vacancies. However, despite a decline in number of territorial males, we observed an altered breeding system with satellites not becoming territorial. Territorial males with neighbors have few heterospecific intruders and we hypothesize territoriality is no longer beneficial to satellites due to the lack of interaction with territorial neighbors. We examine the costs of both strategies in number of intruders present at spawning and benefits in number of spawnings. In addition, large numbers of a pupfish egg predator, the endangered Gambusia nobilis, may be contributing to the decline of C. bovinus. We discuss management implications when one endangered species threatens another.
Computing Multiple Dirichlet Series in a Rational Function Field
Friedberg, Hoffstein and Lieman showed how to construct two related multiple Dirichlet series from quadratic and higher-order twisted L-functions and Gauss sums. We compute these multiple Dirichlet series explicitly in the case of the rational function field. This is done by utilizing the functional equation of the L-functions and the functional equation relating the two multiple Dirichlet series. We also point out a very simple correspondence between the p-parts of these series and their sums.