Developing Methods to Enable Multiplexed Signal Transduction Measurements in Single Cells

Signalling states of cells are heterogeneous even within clonally derived populations due to cell cycle status and their local microenvironment. As a result multiplexed single-cell signal transduction measurements represent a powerful tool which could potentiate a much greater understanding of subcellular processes. However, multiplexed single-cell analysis remains challenging due to several factors, most notably the low copy number of analytes present, difficulties in cellular manipulation and the availability of well characterized and stable probes for use in intact cells. In order to address these issues, a capillary electrophoresis system with laser induced fluorescence (CE-LIF) suitable for screening methods to facilitate single cell analysis was designed and assembled. This system has the requisite sensitivity for single-cell analysis, with the capability of detecting down to 10000 molecules of fluorescein, and has been designed to reduce the time required for analyte separations compared to similar systems by integrating a compact detection module which allows for shorter electrophoretic separation distances. This system has been employed to develop a method to determine the sampling efficiency of laser-based cell lysis of single cells allowing more accurate quantitative measurements of fluorescent peptides from single cells. Furthermore, a fluorescent probe based on amyloid precursor protein (β-APP peptide) has been designed and conditions were found which allowed resolution of enzyme-modified versions within single cells. To identify the enzymatic conversion products produced, a novel method was developed employing bulk cell samples in conjunction with LC-MS. As a testament to the resolution afforded by this technique, the peptide fragments identified from single cells represented peptides which differed by single uncharged amino acids. Together, the methods here developed are able to provide higher quality quantitative data and more informative analysis of fluorescent signal transduction reporters in single cells and represents progress towards being able to obtain highly multiplexed data needed for accurate cellular models.Ph