Analysis of the H-Ras mobility pattern in vivo shows cellular heterogeneity inside epidermal tissue

Abstract

Over the last two decades, developments in single-molecule microscopy (SMM) have enabled imaging and tracking of individual, fluorescently labelled proteins in biological systems, and most of these studies have focused on the analysis of protein mobility patterns inside cultured cells. In the present study, SMM was applied in vivo, using the zebrafish embryo model. We studied the protein dynamics of the membrane protein H-Ras, mutants of this protein, and its membrane-anchoring domain, C10H-Ras, in epidermal cells of living two-day-old embryos, using a total internal reflection fluorescence microscopy (TIRFM) setup. For all proteins studied, our results consistently confirm the presence of a fast- and a slow-diffusing subpopulations of molecules, which both confine to microdomains within the plasma membrane. Although the mobility patterns of H-Ras, mutants of this proteins and its membrane-anchoring domain were remarkably similar, the constitutively active H-Ras mutant, H-RasV12, exhibited significantly higher diffusion rates than the wild-type H-Ras and its inactive mutant, H-RasN17. Ultimately, we characterized variability in our data obtained using the zebrafish embryo model and demonstrated that differences between cells within the same embryo are the largest source of variation in our data. Our findings are in line with a model in which the cellular architecture of individual cells within a tissue determine the mobility of H-Ras proteins anchored in the plasma membrane cytoplasmic leaflet. Thereby, our results underline the growing importance of performing SMM imaging in vivo in order to better understand factors influencing the protein dynamics in an intact living organism. SUMMARY STATEMENTBy application of single-molecule microscopy to living zebrafish embryos, factors altering the in vivo dynamics of H-Ras proteins in epidermal cells were analyzed.