Confocal microscopy-based linescan methodologies for intra-golgi localization of proteins

Localization of resident Golgi proteins to earlier (cis) or later (trans) Golgi compartments has traditionally required quantitative immunocytochemistry and electron microscopy, which are inaccessible to many researchers. For this reason, light microscopy has often been used, initially for localization of Golgi glycotransferases and, more recently, for other Golgi proteins (e.g., Arf1, GBF1, Rab6). Quantitation of light microscopic intra-Golgi localization can be problematic. We describe here a novel quantitative light microscopic methodology using linescans crossing the Golgi ribbon. Our method determines a localization for the unknown protein in a one-dimensional coordinate system in which 0.0 corresponds to localization of a cis marker and 1.0 to localization of a trans marker. We also describe a variant of this methodology in which Golgi morphology is simplified by nocodazole-induced dispersal KEY into ministacks, allowing a fully automated analysis. in our assay, beta 1,4-galactosyltransferase-Golgi YFP and Golgin97 localize similarly to trans markers, whereas p115, GBF1, and p58-YFP are electron microscopy similarly near other cis markers. The medial Golgi protein alpha 1,3-1,6-mannosidase II gives an confocal intermediate localization in this assay. These methodologies may prove useful in instances cis where electron microscopy is technically difficult as well as when rapid analysis of large trans numbers of samples is required.