scRNA-seq of mESC and mouse CD4+ cells using different buffers and enzymes

Existing protocols for full-length single-cell RNA sequencing (scRNA-seq) produce libraries of high complexity (thousands of distinct genes) with outstanding sensitivity and specificity of transcript quantification. These full-length libraries have the advantage of allowing probing of transcript isoforms, are informative regarding single nucleotide polymorphisms, and allow assembly of the VDJ region of the T- and B-cell receptor sequences. Since full length protocols are mostly plate-based at present, they are also suited to profiling cell types where cell numbers are limiting, such as rare cell types during development for instance. A disadvantage of these methods has been the scalability and cost of the experiments, which has limited their popularity as compared to droplet-based and nanowell approaches. Here, we describe an automated protocol for full-length scRNA-seq, including both an in-house automated SMART-seq2 protocol, and a commercial kit-based workflow. We discuss these two protocols in terms of ease-of-use, equipment requirements, running time, cost per sample and sequencing quality. By benchmarking the lysis buffers, reverse transcription enzymes and their combinations, we propose an optimized in-house automated protocol with dramatically reduced cost. These pipelines have been employed successfully for several research projects allied with the Human Cell Atlas initiative (www.humancellatlas.org) and are available on protocols.io.