An epigenetic repressor TRIM66 dictates monogenic olfactory receptor expression, neural activity, and olfactory behavior

Olfactory receptor gene choice is an extremely intricate example of monogenic and monoallelic expression, where one out of over 1,000 receptor genes is transcribed in each olfactory sensory neuron. This process involves expression of multiple olfactory receptor genes in immature neurons, followed by silencing of all but one receptor genes during maturation. However, the molecular identity of the repressors remains mysterious. Here, we discover TRIM66 as a key repressor. Multiple receptor genes are retained at low levels in most single mature OSNs after deletion of Trim66, leading to decreased expression of the vast majority of olfactory receptor genes. Mechanistically, TRIM66 can bind to, assembly, and repress olfactory receptor enhancers, thereby silencing extra olfactory receptor genes. Functionally, deletion of Trim66 leads to severe defects in the olfactory information processing and innate olfactory behaviors. Our study provides the missing link in understanding the transition from polygenic to monogenic olfactory receptor expression. Overall design: To examine the potential role of Trim66 in olfactory receptor (OR) expression, we generated KO and cKO mouse lines and assessed changes in receptor expression following Trim66 deletion (For bulk RNA-seq and scRNA-seq data). To investigate the mechanisms of OR gene regulation by Trim66, we performed ChIP-seq in the MOE of WT mice using antibodies against TRIM66, ATF5, EZH2, and YY1 (For ChIP-seq data). To evaluate changes in chromatin accessibility, We further performed ATAC-seq in the MOE of Trim66 knockout mice (For ATAC-seq data). We further performed Hi-C in Trim66 knockout mice to investigate 3D genome organization (For Hi-C data). Additionally, we carried out CUT&Tag experiments in Olfr1507-expressing OSNs isolated from Olfr1507-ires-tdTomato; Trim66 knockout mice using antibodies against H3K27ac and H3K27me3 to profile histone modifications (For H3K27ac, H3K4me1, H3K9me3, and H3K27me3 data).