Aldehyde fixation of thiol-reactive fluorescent cytoplasmic probes for tracking cell migration

Tracking of cell migration plays an important role in the study of morphogenesis, inflammation, and metastasis. The recent development of probes that exist as intracellular peptide-fluorescence dye adducts has offered the possibility of aldehyde fixation of these dyes for detailed anatomic studies of lymphocyte trafficking. To define the conditions for fixation of these cytoplasmic fluorescent probes, we compared fixation conditions containing formaldehyde, glutaraldehyde, paraformaldehyde, zinc formaldehyde, and glyoxylate, as well as fixation by quick-freezing in liquid nitrogen-cooled methylbutane. The efficacy of aldehyde fixation of the cell fluorescence was assessed by quantitative tissue cytometry and flow cytometry. We studied cytoplasmic fluorescent dyes with discrete emissions in the green [5-chloromethylfluorescein diacetate (CMFDA); 492 ex, 516 em] and orange [5-(and-6)-(4-chloromethyl(benzoyl)amino) tetramethylrhodamine (CMTMR); 540 ex, 566 em] spectra. The results demonstrated that aldehyde fixation preserved cell fluorescence for more than 6 months. The primary difference between the aldehyde fixatives was variability in the difference between the yield of the cell fluorescence and the relevant background fluorescence. Formaldehyde and paraformaldehyde were superior to the other fixatives in preserving cell fluorescence while limiting background fluorescence. With these fixatives, both the CMFDA and CMTMR fluorescent dyes permitted sufficient anatomic resolution for reliable localization in long-term cell tracking studies.