Abstract: The mammalian olfactory system depends on a plethora of olfactory sensory neurons (OSNs), each exclusively expressing a single olfactory receptor (OR) gene, thus specializing each OSN to bind a specific range of odorant chemistries. Specifically in mice, the OR gene family is impressively comprised of >1,500 different OR genes, with expression being monogenic and monoallelic. While this gene regulation mechanism continues to be debated, we focus on a portion of the proposed initial silencing mechanism where previous data suggests that ORs have some level of intrinsic self-silencing capabilities. We transfected one olfactory-placode-derived cell line modeling immature OSNs, with episomal constructs containing cytomegalovirus (CMV)-driven GFP and thymidine kinase-driven hygromycin resistance reporter genes. These episomal constructs were inserted with different OR coding sequences, in addition to an internal ribosome entry site (IRES), upstream of the GFP gene sharing the local CMV promoter. Our data suggests that the presence of several OR coding sequences result in significantly lowered episomal expression of GFP compared to control sequences. These discoveries continue to confirm this portion of the gene regulation mechanism that OR coding sequences possess an intrinsic silencing capability with the plausible goal of assisting in mutually exclusive OR expression in OSNs and to mitigate the likelihood that multiple ORs reach a level of expression above threshold in a single developing OSN.
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