Genome-Wide Expression Analysis ofPtf1a- andAscl1-Deficient Mice Reveals New Markers for Distinct Dorsal Horn Interneuron Populations Contributing to Nociceptive Reflex Plasticity

Abstract

Inhibitory interneurons of the spinal dorsal horn play critical roles in the processing of noxious and innocuous sensory information. They form a family of morphologically and functionally diverse neurons that likely fall into distinct subtypes. Traditional classifications rely mainly on differences in dendritic tree morphology and firing patterns. Although useful, these markers are not comprehensive and cannot be used to drive specific genetic manipulations targeted at defined subsets of neurons. Here, we have used genome-wide expression profiling of spinal dorsal horns of wild-type mice and of two strains of transcription factor-deficient mice (Ptf1a Ϫ/Ϫ and Ascl1/ Mash1 Ϫ/Ϫ mice) to identify new genetic markers for specific subsets of dorsal horn inhibitory interneurons. Ptf1a Ϫ/Ϫ mice lack all inhibitory interneurons in the dorsal horn, whereas only the late-born inhibitory interneurons are missing in Ascl1 Ϫ/Ϫ mice. We found 30 genes that were significantly downregulated in the dorsal horn of Ptf1a Ϫ/Ϫ mice. Twenty-one of those also showed reduced expression in Ascl1 Ϫ/Ϫ mice. In situ hybridization analyses of all 30 genes identified four genes with primarily non-overlapping expression patterns in the dorsal horn. Three genes, pDyn coding the neuropeptide dynorphin, Kcnip2 encoding a potassium channel associated protein, and the nuclear receptor encoding gene Rorb, were expressed in Ascl1-dependent subpopulations of the superficial dorsal horn. The fourth gene, Tfap2b, encoding a transcription factor, is expressed mainly in a Ascl1-independent subpopulation of the deep dorsal horn. Functional experiments in isolated spinal cords showed that the Ascl1-dependent inhibitory interneurons are key players of nociceptive reflex plasticity.

Transmitting Pain and Itch Messages: A Contemporary View of the Spinal Cord Circuits that Generate Gate Control

“…These populations do not overlap and account for ~65% of inhibitory interneurons in lamina I and ~50% in lamina II (Sardella et al, 2011). More recently, subsets of inhibitory interneurons have been defined by the different transcription factors that regulate their development (Ross et al, 2010; Wildner et al, 2013). …”

Identification of a cellular node for motor control pathways

“…We identified three candidate genes that are expressed in the medial deep dorsal horn at embryonic and postnatal stages, the transcription factor Tfap2b (also known as Tcfap2β ) and the nuclear and chromatin organization factors Satb1 and Satb2 (refs. 30,31). Tcfap2β is expressed at late embryonic and early postnatal stages across lamina V (with overlap into laminae IV and VI) and in a few scattered cells in the ventral horn (Fig.…”

Making sense out of spinal cord somatosensory development

“…Thus, terminal neuronal phenotypes can be directly regulated by sustained expression of HD factors in mature neurons. Furthermore, transiently expressed TFs, such as the bHLH TFs ATOH1, PTF1A and ASCL1, have been shown to directly regulate genes that control terminal neuronal phenotypes in addition to their role in regulating the expression of HD TFs (Borromeo et al, 2014;Lai et al, 2011;Russ et al, 2015;Wildner et al, 2013). For example, PTF1A directly regulates genes encoding GABA synthesizing enzymes and GABA and glycine transporters required for inhibitory neuronal functions, but it also regulates the expression of PAX2 (Borromeo et al, 2014).…”