Drake H. Harbert
The sigma-1 receptor (SIGMAR1) and sigma-2 receptor (TMEM97) are both enriched at the mitochondria-associated membrane (MAM) and have been pharmacologically co-classified for decades, yet their functional relationship at the transcriptomic level remains uncharacterized. We performed genome-wide co-expression analysis for both receptors across five brain regions from the GTEx v8 dataset (n = 209 in the primary region, 16,225 expressed genes) using Spearman correlations. Three Weighted Jaccard (WJ) formulations on continuous correlation vectors — (r+1)/2 shifted, unsigned |r|, and signed—all revealed that SIGMAR1 and TMEM97 share the majority of their global transcriptional architecture (WJ shifted = 0.964, unsigned = 0.907, signed = 0.906; all three rank-identical across 21 pairwise comparisons, ρ = 1.000), yet their top 5% co-expression networks overlap by only 10.0% (binary Jaccard = 0.100). Cosine similarity on raw vectors confirmed metric robustness (ρ = 0.856 with WJ, p = 7.5 × 10 −7 ). Dissociation gap analysis across all 21 gene pairs showed the WJ-binary gap varies 2.1-fold (0.431–0.927), tracking known biological relatedness rather than reflecting a fixed methodological property. Gene Ontology analysis identified SIGMAR1-specific enrichment for mitochondrial translation and TCA cycle, and TMEM97-specific enrichment for ubiquitin-mediated proteolysis and neurodegeneration pathways. Multi-region replication confirmed the pattern across five brain regions, with the hippocampus showing tail-specific convergence. These findings are consistent with the hypothesis that dual sigma-1/sigma-2 ligands engage two functionally distinct co-expression programs within a shared cellular context, providing a transcriptomic rationale for subtype-selective pharmacological strategies.