Spatial Single Cell Analysis of Proteins in 2D Human Gastruloids Using Iterative Immunofluorescence.

During development, cell signaling instructs tissue patterning, the process by which initially identical cells give rise to spatially organized structures consisting of different cell types. How multiple signals combinatorially instruct fate in space and time remains poorly understood. Simultaneous measurement of signaling activity through multiple signaling pathways and of the cell fates they control is critical to addressing this problem. Here we describe an iterative immunofluorescence protocol and computational pipeline to interrogate pattern formation in a 2D model of human gastrulation with far greater multiplexing than is possible with standard immunofluorescence techniques. This protocol and computational pipeline together enable imaging followed by spatial and co-localization analysis of over 27 proteins in the same gastruloids. We demonstrate this by clustering single cell protein expression, using techniques familiar from scRNA-seq, and linking this to spatial position to calculate spatial distributions and cell signaling activity of different cell types. These methods are not limited to patterning in 2D gastruloids and can be easily extended to other contexts. In addition to the iterative immunofluorescence protocol and analysis pipeline, Support Protocols for 2D gastruloid differentiation and producing micropatterned multi-well slides are included. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Iterative immunofluorescence Basic Protocol 2: Computational analysis pipeline Support Protocol 1: Generating micropatterned multi-well slides Support Protocol 2: Differentiation of 2D gastruloids.