Prenatal alcohol exposure results in brain region- and sex-specific changes in circHomer1 expression in adult mouse brain

Abstract

Circular RNAs (circRNAs) are a novel category of covalently-closed non-coding RNAs mainly derived from the back-splicing of exons or introns of protein-coding genes. In addition to their inherent high overall stability, circRNAs, have been shown to have strong functional effects on gene expression via a multitude of transcriptional and post-transcriptional mechanisms. Furthermore, circRNAs, appear to be particularly enriched in the brain and able to influence both prenatal development and postnatal brain function. However, little is known about the potential involvement of circRNAs in the long term influence of prenatal alcohol exposure (PAE) in the brain and their relevance for Fetal Alcohol Spectrum Disorders (FASD). Using circRNA-specific quantification, we have found that circHomer1, an activity-dependent circRNA derived from Homer protein homolog 1 (Homer1) and enriched in postnatal brain, is significantly down-regulated in the male frontal cortex and hippocampus of mice subjected to modest PAE. Our data further suggest that the expression of H19, an imprinted embryonic brain-enriched long non-coding RNA (lncRNA), is significantly up-regulated in the frontal cortex of male PAE mice. Furthermore, we show opposing changes in the developmental- and brain region specific- expression of circHomer1 and H19. Lastly, we show that knockdown of H19 results in robust increases in circHomer1 but not linear HOMER1 mRNA expression in human glioblastoma cell lines. Taken together, our work uncovers notable sex- and brain region-specific alterations in circRNA and lncRNA expression following PAE and introduces novel mechanistic insights with potential relevance to FASD.

Regulation of neuronal circHomer1 biogenesis by PKA/CREB/ERK-mediated pathways and effects of glutamate and dopamine receptor blockade.

“…Here we provide strong evidence that CREB, known to promote gene expression in a neuronal activitydependent pattern 39 , is a major positive regulator of circHomer1 biogenesis in neurons, affecting the transcription of Eif4a3 and Fus, genes coding RBPs that promote circHomer1 biogenesis 35,40 . We show that upstream of CREB, the ERK/MAPK and PKA pathways, which are crucial regulators of synaptic plasticity, are involved in the control of Eif4a3 and Fus expression and subsequently circHomer1 biogenesis.…”

“…We have previously shown that EIF4A3 can bind to circHomer1 and positively regulate its expression, identifying EIF4A3 as an upstream regulator of circHomer1 synthesis 35 . In addition, we recently showed that the imprinted lncRNA H19 , which has been previously shown to bind to EIF4A3 and obstruct its recruitment to downstream RNA targets, is a negative regulator of neuronal circHomer1 biogenesis and displays opposing developmental expression within the brain 40 . In order to identify additional factors that could modulate circHomer1 biogenesis, we searched the literature for RBPs enriched in the brain that could bind to EIF4A3 and have either been shown to or been predicted to bind to circHomer1 .…”