Laser-capture microdissection for spatial transcriptomics of immunohistochemically detected neurons

We developed a versatile 'IHC/LCM-Seq' method for spatial transcriptomics of immunohistochemically detected neurons collected with laser-capture microdissection (LCM). IHC/LCM-Seq uses aluminon and polyvinyl sulfonic acid for inventive RNA-preserving strategies to maintain RNA integrity in free-floating sections of 4% formaldehyde-fixed brains. To validate IHC/LCM-Seq, we first immunostained and harvested striatal cholinergic interneurons with LCM. RNA preparations were subjected to random primer-based cDNA library preparation and bulk sequencing on the NextSeq Illumina platform. IHC/LCM-Seq detected ∼16,000 transcripts, reaching the sensitivity of a reference 'LCM-Seq method' developed for fluorescently tagged neurons microdissected from lightly formaldehyde-fixed and slide-mounted brain sections of transgenic mice. We successfully used the new IHC/LCM-Seq approach to provide unprecedented insight into the transcriptome of immunohistochemically detected gonadotropin-releasing hormone (GnRH) neurons regulating reproduction. The ∼13,000 to 14,000 transcripts identified in GnRH neurons of adult male rats and mice encoded 28 proteins implicated previously in human infertility, 35 neuropeptides, 34 nuclear receptors, and 164 G protein-coupled receptors. Functional experiments using slice electrophysiology established that the heavy Ntsr2 expression conveys a strong excitatory action of neurotensin on GnRH neurons. As an unexpected species difference, we found that GnRH neurons exclusively expressed estrogen receptor-β in rats and against the current consensus, the alpha estrogen receptor isoform in mice. The IHC/LCM-Seq technique we are reporting is a highly sensitive and accurate bulk sequencing approach to characterize the transcriptome landscape of immunohistochemically labeled neurons, including neuroendocrine GnRH cells. This method is readily applicable to any species, opening new perspectives also for future studies of the post mortem human brain.