Fingerprinting subclasses of proprioceptors with single cell transcriptomics
Anil Sharma1, Haohao Wu1, Carmelo Bellardita2, Yang Xuan1, Konstantinos Meletis1, Ole Kiehn2, Francois Lallemend1
1Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden; 2Mammalian locomotor laboratory, Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
Sensory feedback from skeletal muscles is essential for coordinated motor control. The gatekeepers of this feedback are the proprioceptive sensory neurons (PSNs) sitting in the dorsal root ganglia. PSNs include subtypes Ia, Ib, and II, differing in anatomy and physiology. Currently, only electrophysiology could discriminate the PSNs subtypes, critically hindering investigations into these important neurons and the sensory-motor circuits of which they are a part. Here we address this problem, uncovering the genetic identities of the PSN subtypes in mice using a combination of mouse genetics, retrograde tracing and single cell transcriptomics.
We have achieved single cell transcriptome profile of PSNs at both embryonic stage E16.5 and adulthood. 297 E16.5 PSNs are clustered into subclasses, of which genetic markers are examined by RNA-ISH. We have successfully employed retrograde tracing of Ia PSNs by injection of Rhodamine-Dextran in the ventral spinal cord of E16.5 embryos. The identities of the subclasses by co-localization of their genetic markers and Rhodamine positivity, suggesting one subclass to be most probably Ia PSNs.
Similarly, 1302 adult PSNs are clustered into subclasses unbiasedly. Using Egr3::WGA mice in which Ia and II PSNs are filled with wheat germ agglutinin(WGA), we are currently validating the identities of adult PSNs subclasses by co-localization analysis of their genetic markers and WGA. To match with subtype-specific anatomy, we will further investigate those subclasses by looking into their synaptic partners using immunohistochemistry.
Our final aim is to generate mouse lines to allow in vivo and in vitro labelling and manipulation of PSNs subtypes.