Department of Biophysics and Biophysical Chemistry
School of Medicine
B.S. 1995, Nanjing University
Ph.D. 2002, Rice University
725 N. Wolfe Street
Baltimore, MD 21205
My research group focuses on bacterial cell division, transcription and gene regulation. We combine sensitive, high resolution single-molecule methods with well established genetic and biochemical methods to address challenges in bacterial cell biology.
Dynamics and structure of the division complex
Prokaryotic cell division is a conserved process that requires the formation of a multi-protein complex (termed divisome) to carry out constriction. Although many of the molecular constituents have been identified, the structural organization of the divisome remains elusive. The central component of the divisome is FtsZ, a highly conserved prokaryotic tubulin homolog that polymerizes at midcell to form a ring-like structure (termed the Z-ring). The FtsZ-ring is not only required for the assembly of all other division proteins, but may also generate a constrictive force during cytokinesis. We are interested in understanding how FtsZ and other components of the divisome are orchestrated to function and coordinate with other essential cellular events. Specifically, we focus on the following questions in E. coli cells:
1. What is the structural organization of the divisome?
2. How does the divisome reorganize during cell wall constriction?
3. What's the mechanism for force generation during cell wall constriction?
Toward these goals we established single-molecule based superresolution imaging methods to illustrate the structure and dynamics of the FtsZ-ring with its associated proteins. Our recent publications can be found below [2, 7, 8, 11].
Spatial organization and dynamics of transcription
Prokaryotic transcription has been extensively studied in the past half a century. However, there often exists a gap between the structural, mechanistic description of transcription obtained from in vitro biochemical studies, and the cellular, phenomenological observations from in vivo genetic studies. It is now accepted that a living bacterial cell is a complex entity; the heterogeneous cellular environment is drastically different from the homogenous, well-mixed situation in vitro. Where molecules are inside a cell may be important for their functions. Hence, examining the in-vivo spatial organization and dynamics of transcription in live cells is of particular important in finding new insight, possibly bridging the gap. See these publications below for how we think of this problem [1, 5].
Noise control mechanism in gene regulatory networks
Gene expression is stochastic in nature as the components involved exist in small copy numbers. Such stochasticity inevitably leads to output noise. However, "Noisy gene expression" is intuitively at odds with the reliable formation of precise gene expression patterns cells and organisms exhibit during development and growth. How do cells function with amazing precisions when the underlying molecular events are inherently stochastic? To answer this question, we have developed single-molecule gene expression fluorescence reporters that allow us to directly monitor the production of single protein molecules including transcription factors in real time. See these publications below for a few examples about how we address this problem [6, 10, 12, 19].
1. Weng, X., and J. Xiao. (2014) Spatial organization of transcription in bacterial cells. Trends Genet. (in press)
2. Buss, J., C. Coltharp, T. Huang, C. Pohlmeyer, C. Hatem, and J. Xiao. (2013) In vivo organization of the FtsZ-ring by ZapA and ZapB revealed by quantitative super-resolution microscopy. Mol. Microbio. 89:1099-1120. doi: 10.1111/mmi. 12331
3. Buss, J., C. Coltharp, and J. Xiao. (2013) Super-resolution imaging of the bacterial division machinery. J. Vis. Exp 71:e50048. doi: 10.3791/50048
4. Hensel, Z., X. Fang, and J. Xiao. (2013) Single-molecule imaging of gene regulation in vivo using Co-Translational Activation by Cleavage (CoTrAC). J. Vis. Exp 73:e50042. doi: 10.3791/50042
5. Hensel, Z., X. Weng, A. Lagda, and J. Xiao. (2013) Transcription factor mediated DNA looping probed by high-resolution, single-molecule imaging in live E. coli cells. PLoS Biol. 11:e1001591.
6. Hensel, Z., and J. Xiao. (2013) Single molecule methods for studying gene regulation in vivo. Pflugers Arch. 465:383-395. (selected for cover image)
7. Coltharp, C., R. Kessler, and J. Xiao. (2012) Accurate construction of photoactivated localization microscopy (PALM) images for quantitative measurements. PLoS ONE 7:e51725. doi: 10.1371
8. Coltharp, C., and J. Xiao. (2012) Superresolution microscopy for microbiology. Cell Microbiol. 14:1808-1818.
9. Feng, H., Z. Hensel, J. Xiao*, and J. Wang*. (2012) Analytical calculation of protein production distributions in models of clustered protein expression. Phys. Rev. Lett. E 85:031904.
10. Hensel, Z., H. Feng, B. Han, C. Hatem, J. Wang*, and J. Xiao*. (2012) Stochastic expression dynamics of transcription factor revealed by single-molecule noice analysis. Nat. Struct. Mol. Biol. 19:797-802. (selected for cover image)
11. Fu, G., T. Huang, J. Buss, C. Coltharp, Z. Hensel, and J. Xiao. (2010) In vivo structure of the E. coli FtsZ-ring revealed by Photoactivated Localization Microscopy (PALM). PLoS ONE 5:e12680.
12. Hensel, Z., and J. Xiao. (2009) A mechanism for stochastic decision making by bacteria. Chembiochem. 10:974-976.
13. Xiao, J. (2009) Single molecule imaging in live cells. In Handbook of Single-molecule Biophysics, ed. by van Oljen, and Hinterdorfer. New York: Springer.
14. Singleton, S.F., A.I. Roca, A.M. Lee, and J. Xiao. (2007) Probing the structure of RecA-DNA filaments. Advantages of a fluorescent guanine analog. Tetrahedron 63:3553-3566.
15. Xiao, J., J. Elf, G. Li, J. Yu, and X.S. Xie. (2007) Imaging gene expression in living cells at the single molecule level. In Single Molecules: A Laboratory Manual, ed. by Selvin, and Ta. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.
16. Lee, A.M., J. Xiao, and S.F. Singleton. (2006) Origins of sequence selectivity in homologous genetic recombination: insights from rapid kinetic probing of RecA-mediated DNA strand exchange. J. Mol. Biol. 360:343-359.
17. Xiao, J., A.M. Lee, and S.F. Singleton. (2006) Direct evaluation of a kinetic model for RecA-mediated DNA-strand exchange: the importance of nucleic acid dynamics and entropy during homologous genetic recombination. Chembiochem. 7:1265-1278.
18. Xiao, J., A.M. Lee, and S.F. Singleton. (2006) Construction and evaluation of a kinetic scheme for RecA-mediated DNA strand exchange. Biopolymers 81:473-496.
19. Yu*, J., Xiao*, J., X. Ren, K. Lao, and X.S. Xie. (2006) Probing gene expression in live E. coli cells: one molecule at a time. Science 311:1600-1603.
*first two authors contributed equally to the work.
20. Xiao, J., and S.F. Singleton. (2002) Elucidating a key internediate in homologous DNA strand exchange: structural characterization of the RecA-triple-stranded DNA complex using fluorescence resonance energy transfer. J. Mol. Biol. 320:529-558.
21. Singleton, S.F., and J. Xiao. (2001) The stretched DNA geometry of recombination and repair nucleoprotein filaments. Bipolymers 61:145-158.
22. Martin, S.R., A.Q. Lu, J. Xiao, J. Kleinjung, K. Beckingham, and P.M. Bayley. (1999) Conformational and metal-binding properties of androcam, a testis-specific, calmodulin-related protein from Drosophila. Protein Sci. 8:2444-2454.