Gillian Stanfield
Research Assistant Professor of human genetics
A.B. University of Chicago
Ph.D. Massachusetts Institute of Technology
Research
Sperm are fascinating motile cells whose purpose is to locate and fuse with an egg in order to accomplish sexual reproduction. We are interested in how sperm functions can be modulated to influence a male’s reproductive success. To study this process, we are using the nematode C. elegans, which offers many advantages for the study of reproduction. C. elegans exists as two sexes: males and self-fertilizing hermaphrodites, so male reproductive success inevitably involves competition with a hermaphrodite’s self sperm, and in C. elegans, we can assay the differentiation and function of individual sperm cells in vivo or in vitro.
Sperm differentiation
Nematode sperm are amoeboid and move by crawling; however, like sperm with flagella, they must undergo an elaborate process of spermiogenesis (termed activation) to transform round haploid spermatids into highly differentiated, polarized spermatozoa capable of motility and fertilization. We seek to understand the sex-specific and spatiotemporal signals that regulate sperm activation. We have identified a protease inhibitor that is required for male fertility and functions to prevent premature sperm activation from occurring within males. Using this mutant, we have found that activation must be delayed in males to allow their sperm to be transferred to a hermaphrodite. We are using a variety of genetic and molecular approaches to understand how proteases regulate sperm activation and to identify other molecules involved in triggering this cellular reorganization.
Sperm competition
If male sperm are available within the C. elegans hermaphrodite reproductive tract, they are used preferentially. Previous experiments designed to test specific models of sperm competition indicated that male precedence appears to be due to a sperm-intrinsic factor(s) and correlates with the larger size of male sperm. However, the molecular basis of this phenomenon is not understood. We are using genetic screens to identify factors important for male sperm precedence. This strategy should yield insights into general mechanisms of the cellular interactions between sperm and the female reproductive tract, egg, and other sperm.
Paired DIC and fluorescence images of a hermaphrodite gonad containing mitotracker red-labeled male sperm. The male sperm have migrated through the uterus to the hermaphrodite’s spermathecae, where fertilization will occur. Labels: ov, oviduct; spth, spermatheca, ut, uterus.
References
1. Stanfield GM, Villeneuve AM (2006) Regulation of Sperm Activation by SWM-1 Is Required for Reproductive Success of C. elegans Males. Current Biology 16:252-263
2. Colaiácovo MP, Stanfield GM, Reddy KC, Reinke V, Kim SK, Villeneuve AM (2002) A Targeted RNAi Screen for Genes Involved in Chromosome Morphogenesis and Nuclear Organization in the Caenorhabditis elegans Germline. Genetics 162:113-128
3. Kelly KO, Dernburg AF, Stanfield GM, Villeneuve AM (2000) Caenorhabditis elegans msh-5 is Required for Both Normal and Radiation-Induced Meiotic Crossing Over but Not for Completion of Meiosis. Genetics 156:617-630
4. Wu YC*, Stanfield GM*, Horvitz HR (2000) NUC-1, a C. elegans DNase II homolog, functions in an intermediate step of DNA degradation during apoptosis. Genes and Development 14:536-548 *Contributed equally
5. Stanfield GM, Horvitz HR (2000) Mutations in the ced-8 gene alter the timing of programmed cell deaths in C. elegans. Molecular Cell 5:423-433
