One probe fits all: a highly customizable modular RNA in situ hybridization platform expanding the application of SABER DNA probes

In situ hybridization (ISH) of RNA is a key method to visualize gene expression patterns in complex biological samples. The technique is indispensable for biological research related to e.g. development, disease, gene function, and the validation of novel cell types identified by single-cell sequencing methods. Especially in non-mammalian models lacking accessibility to a broad spectrum of antibodies, ISH remains a major research tool. Diverse available ISH protocols require different custom hybridization probe types, design, and/or proprietary signal detection chemistry. This makes it hard to navigate for a beginner and increases the research costs when multiple methods need to be applied. Here, we describe OneSABER - a unified open platform connecting commonly used canonical and recently developed single- and multiplex, colorimetric, and fluorescent ISH approaches. This platform uses a single type of ISH DNA probes adapted from the signal amplification by exchange reaction (SABER) method. We demonstrate applications of the proposed ISH framework in whole-mount samples of the regenerative flatworm Macrostomum lignano, advancing this animal as a powerful model for stem cell and regeneration research.