LAUSR

Simple Summary Gene expression controls all aspects of life, including that of humans. Genes are expressed by copying the information stored in the DNA into RNA molecules, and this process is regulated in part by multiple RNA-binding proteins (RBPs). One such protein, HuD, plays a critical role in the development of neurons and has been implicated in childhood brain tumors, neurodegenerative disorders (Parkinson’s, Alzheimer’s, and ALS), and drug abuse. In addition, HuD participates in neuronal remodeling mechanisms in the mature brain and promotes regeneration of peripheral nerves. HuD primarily binds to transcribed messenger RNAs, which are then stabilized for translation into proteins. However, recent studies demonstrate that HuD also regulates the expression of non-coding RNAs, such as circular RNAs (circRNAs) and microRNAs (miRNAs). In this study, we examined the role of HuD in the control of non-coding RNA expression in the mouse striatum, a brain region associated both with normal behaviors and pathological conditions such as drug abuse. Our results show that HuD regulates mRNA-circRNA-miRNA networks involved in the expression of genes associated with brain development and remodeling of neuronal connections. These findings suggest the possibility of new mechanisms controlling brain development, neurodegenerative diseases, and substance use disorders. Abstract The RNA-binding protein HuD (a.k.a., ELAVL4) is involved in neuronal development and synaptic plasticity mechanisms, including addiction-related processes such as cocaine conditioned-place preference (CPP) and food reward. The most studied function of this protein is mRNA stabilization; however, we have recently shown that HuD also regulates the levels of circular RNAs (circRNAs) in neurons. To examine the role of HuD in the control of coding and non-coding RNA networks associated with substance use, we identified sets of differentially expressed mRNAs, circRNAs and miRNAs in the striatum of HuD knockout (KO) mice. Our findings indicate that significantly downregulated mRNAs are enriched in biological pathways related to cell morphology and behavior. Furthermore, deletion of HuD altered the levels of 15 miRNAs associated with drug seeking. Using these sets of data, we predicted that a large number of upregulated miRNAs form competing endogenous RNA (ceRNA) networks with circRNAs and mRNAs associated with the neuronal development and synaptic plasticity proteins LSAMP and MARK3. Additionally, several downregulated miRNAs form ceRNA networks with mRNAs and circRNAs from MEF2D, PIK3R3, PTRPM and other neuronal proteins. Together, our results indicate that HuD regulates ceRNA networks controlling the levels of mRNAs associated with neuronal differentiation and synaptic physiology.