User:GeorgeXu

About Me

I am currently a graduate student in the joint program between Harvard Biophysics and HST.

Research History

2005 Summer

I studied Berry Shrivel Disease under the mentorship of Professor Ken Shackel and Dr. Mark Krasnow at UC Davis's Department of Viticulture and Enology through the Young Scholar's Program. I imaged grape berry sections bathed in fluorescein diacetate, which is intracellularly hydrolyzed by viable cells to the fluorescent protein fluorescein [1], in order to assess cell viability in diseased grapes. Our hypothesis was that the disease was caused by massive cell death, in particular the companion cells surrounding the phloem. I had to leave for school before distinct symptoms presented and my data could be analyzed, but later analysis proved inconclusive. I can no longer find the CD with all of my 1000+ awesome images, but you can see a sample on slide 23 of Dr. Krasnow's presentation.

2007 Spring

During the second semester of my freshman year, I briefly worked part-time in the Weitz Lab with Dr. Amy Rowat on a microfluidics device for fluorescent detection, actuation, and control of individual yeast cells for directed evolution studies.

2007 Summer - 2007 Winter

During the summer following my freshman year I was a member of Harvard's 2007 iGEM team. The overall goal of our project was to have bacteria that would bind to a target and activate a signal, either through quorum sensing or transmembrane signal transduction. Our project consisted of three modules:

1. We planned to utilize surface expression of a peptide library through fusion with the surface proteins Lpp-OmpA [2] and autodisplay protein AIDA-1 [3] for screening of binding sequences. We were able demonstrate successful fusion and targeting with his and strep2 tags but did not have time to test a random library.
2. The project that I helped brainstorm was the quorum sensing. We utilized LuxI/LuxR quorum sensing found in V. fishcheri to create two systems: one was a single-cell that created both the "sender" LuxI molecule and the "receiver" luxR molecule, while the other had the "sender" and "receiver" constructs in separate cells. We successfully demonstrated quorum sensing in our system and began tests of combining these constructs with surface expression. My work on this project is (mostly) documented in my iGEM Lab Notebook.
3. We planned to construct transmembrane signal transduction using the Fec system [4]. Unfortunately, the project turned out to be too ambitious and we were unsuccessful.

Professor George Church was one of the faculty advisors for this program and one of his students, Harris Wang, was one of the Teaching Fellows. After the iGEM jamboree, I began working for Harris in the Church lab.

2008 Summer

During the summer following my sophomore year I received generous funding from the Harvard Reischauer Institute's Summer Internship Program to work in Japan for 10 weeks. While there, I prepared and published a review article under the mentorship of Masakazu Umezawa and Professor Ken Takeda on the permanent health effects of adverse fetal environments.

2008 Spring - 2010 Spring

I worked in the Church lab with Harris Wang and Dr. Farren Isaacs on lambda-red mediated recombineering [5]. Most of my work is documented on an internal lab wiki.

Publications

1. Wang HH, Isaacs FJ, Carr PA, Sun ZZ, Xu G, Forest CR, and Church GM. 'Programming cells by multiplex genome engineering and accelerated evolution'. Nature. 460, 894 (2009)

References

1. Heslop-Harrison J and Heslop-Harrison Y. Evaluation of pollen viability by enzymatically induced fluorescence; intracellular hydrolysis of fluorescein diacetate. Stain Technol. 1970 May;45(3):115-20. DOI:10.3109/10520297009085351 |
2. Earhart CF. Use of an Lpp-OmpA fusion vehicle for bacterial surface display. Methods Enzymol. 2000;326:506-16. DOI:10.1016/s0076-6879(00)26072-2 |
3. Maurer J, Jose J, and Meyer TF. Autodisplay: one-component system for efficient surface display and release of soluble recombinant proteins from Escherichia coli. J Bacteriol. 1997 Feb;179(3):794-804. DOI:10.1128/jb.179.3.794-804.1997 |
4. Koebnik R, Locher KP, and Van Gelder P. Structure and function of bacterial outer membrane proteins: barrels in a nutshell. Mol Microbiol. 2000 Jul;37(2):239-53. DOI:10.1046/j.1365-2958.2000.01983.x |
5. Thomason L, Court DL, Bubunenko M, Costantino N, Wilson H, Datta S, and Oppenheim A. Recombineering: genetic engineering in bacteria using homologous recombination. Curr Protoc Mol Biol. 2007 Apr;Chapter 1:Unit 1.16. DOI:10.1002/0471142727.mb0116s78 |
6. Berg HC and Purcell EM. Physics of chemoreception. Biophys J. 1977 Nov;20(2):193-219. DOI:10.1016/S0006-3495(77)85544-6 |