MicroSAGE: a modified procedure for serial analysis of gene expression in limited amounts of tissue

Serial Analysis of Gene Expression (SAGE) is a powerful expression profilin g method, allowing the analysis of the expression of thousands of transcrip ts simultaneously, A disadvantage of the method, however, is the relatively high amount of input RNA required. Consequently, SAGE cannot be used for t he generation of expression profiles when RNA is limited, i.e. in small bio logical samples such as tissue biopsies or microdissected material. Here we describe a modification of SAGE, named microSAGE, which requires 500- to 5 000-fold less starting material. Compared with SAGE, microSAGE is simplifie d due to incorporation of a 'single-tube' procedure for all steps from RNA isolation to tag release, Furthermore, a limited number of additional PCR c ycles are performed. Using microSAGE gene expression profiles can be obtain ed from minute quantities of tissue such as a single hippocampal punch from a rat brain slice of 325 mu m thickness, estimated to contain, at most, 10 (5) cells. This method opens up a multitude of new possibilities for the ap plication of SAGE, for example the characterization of expression profiles in tissue biopsies, tumor metastases or in other cases where tissue is scar ce and the generation of region-specific expression profiles of complex het erogeneous tissues.