Graduate Exam Abstract

Xinran Xu

Ph.D. Final
July 8, 2019, 10:00 am - 12:00 pm
Phoenix Design Studio, Scott Bioengineering Building
Super-resolution imaging and modeling of murine sperm capacitation process

Abstract: The effort to achieve better spatial resolution beyond the diffraction limit has been dedicated
for many years. In the past decade super-resolution microscopy methods have successfully
advanced into extremely powerful tools to reveal hidden three dimensional structures
and properties in various biological complex systems. Here we use single molecule
based three dimensional super-resolution microscopy to study the mouse sperm capacitation
process, a critical step in gaining the fertilization ability. On top of that, we construct a
stochastic model to represent this signaling pathway in order to be able to predict the cellular
event within the capacitation.
The major subjects we are interested in can be categorized into two parts: actin-based
cytoskeleton and capacitation-associated signaling proteins. In the midpiece, we discovered
that F-actin forms a highly specialized double helical structure, which has been the very
first observation among species and has disappeared in the principal piece. Similarly, the
distinctive compartments regarding actin-binding proteins have also been visualized in the
mouse sperm tail.
Additionally, the structure as well as localization of capacitation central mediator, protein
kinase A have been investigated to address the signi ficance of spatial positioning during
the capacitation event. As the capacitation end point reporter, tyrosine phosphorylation
has been studied to help identify its real upstream kinase among other candidates.
As in many regulating processes, second messenger Ca plays a vital role in the capacitation
process, which needs to be conveyed by the sperm specifi c calcium channel CatSper. We
show the structural relation of a small GTPase Cdc42 to CatSper, implying its key role in
transporting Ca.
Considering that major critical signaling molecules are well characterized in the complex
capacitation network, we choose a different method{stochastic modeling, other than
studies, surpassing the need for probing the behavior of a large number of individual
cells over time, to describe capacitation process and furthermore to predict the behavior of
sperm. With the known pathways of those signaling molecules in hand, we are able to build
a stochastic model by utilizing chemical master equations. A couple sets of experimental
measurements are used to assist in quantifying the model.

Adviser: Diego Krapf
Co-Adviser: N/A
Non-ECE Member: Michael Tamkun, Biomedical Science
Member 3: Ali Pezeshki, Electrical and Computer Engineering
Addional Members: Brian Munsky, Chemical and Biological Engineering

1. Alvau, A., Battistone, M. A., Gervasi, M. G., Navarrete, F. A., Xu, X., Sanchez-Cardenas, C., ... & Krapf, D. (2016). The tyrosine kinase FER is responsible for the capacitation-associated increase in tyrosine phosphorylation in murine sperm. Development, 143(13), 2325-2333
2. Gervasi, M. G., Xu, X., Carbajal-Gonzalez, B., Buffone, M. G., Visconti, P. E., & Krapf, D. (2018). The actin cytoskeleton of the mouse sperm flagellum is organized in a helical structure. J Cell Sci, 131(11), jcs215897.
3. Romarowski, A., Felix, A. G. V., Rodríguez, P. T., Gervasi, M. G., Xu, X., Luque, G. M., ... & Visconti, P. E. (2018). Super-resolution imaging of live sperm reveals dynamic changes of the actin cytoskeleton during acrosomal exocytosis. J Cell Sci, 131(21), jcs218958.
4. Stival, C., Ritagliati, C., Xu, X., Gervasi, M. G., Luque, G. M., Graf, C. B., ... & Buffone, M. G. (2018). Disruption of protein kinase A localization induces acrosomal exocytosis in capacitated mouse sperm. Journal of Biological Chemistry, 293(24), 9435-9447.
5. Krapf, D., Marinari, E., Metzler, R., Oshanin, G., Xu, X., & Squarcini, A. (2018). Power spectral density of a single Brownian trajectory: what one can and cannot learn from it. New Journal of Physics, 20(2), 023029.
6. Krapf, D., Lukat, N., Marinari, E., Metzler, R., Oshanin, G., Selhuber-Unkel, C., ... & Xu, X. (2019). Spectral content of a single non-Brownian trajectory. Physical Review X, 9(1), 011019.

Program of Study: