Spatially resolved quantification of E-cadherin on target hES cells.

The local expression and distribution pattern of protein on a cell play essential roles in signal transduction within a cell or between cells. Here we report on the development of a spatially resolved quantification method, which was applied in the study of E-cadherin local expression in identified undifferentiated and differentiated human embryonic stem (hES) cells in their native cellular environment. This was achieved by a novel immunofluorescence assisted affinity mapping (IF-AM) method, in which immunofluorescence provides the guidance to locate a desired type of cell in a cell community for performing affinity mapping to quantify the local protein density. The results unveiled the crucial role of E-cadherin in mediating hES cell proliferation and differentiation: the expression of E-cadherin is markedly higher on undifferentiated cells, and the growth of hES cells in unique colonies is contingent on the homogeneous distribution of E-cadherin. Due to the ability of directly assessing individual proteins of a cell, the IF-AM method is shown to be a sensitive tool for resolving subtle differences in the local expression of membrane proteins even at low abundance.