Transcript buffering and 3'UTR lengthening are shaped during human neurodevelopment by shifts in mRNA stability and microRNA load

The change in abundance of individual mRNAs as cells differentiate through neurodevelopmental stages is generally attributed to transcription level alterations while the potential contribution of mRNA half-life is commonly overlooked. While some genes are regulated solely by transcription, others may be regulated by mRNA half-life only, or genes with changed transcription rates could be buffered by compensating half-life decreases or even boosted by amplifying half-life increases. In addition, during neurodevelopment there is widespread 3'UTR lengthening that could be shaped by differential shifts in the stability of transcript isoforms. Here we measure transcription rate and mRNA half-life changes during induced Pluripotent Stem Cell-derived neuronal development using RATE-seq at the resolution of gene isoforms. We found that during transitions to progenitor and neuron stages, transcript buffering occurs in up to half of all genes. Half-life only changes are observed in as many genes as transcription rate only changes, and almost 10% of genes exhibit transcript boosting. Global mRNA half-life decreases two-fold in neurons relative to iPSCs. The observed mRNA destabilization differentially affects gene isoforms and contributes to 3'UTR lengthening. Small RNA sequencing further captured an increase in microRNA copy number per cell. We propose that mRNA destabilization and 3'UTR lengthening are driven in part by an increase in microRNA load. Our findings identify mRNA stability mechanisms in human neurodevelopment that regulate gene and isoform level abundance and provide a precedent for similar post-transcriptional regulatory events as other tissues develop. Overall design: Human iPSCs and iPSC-derived neuronal progenitor cells were subjected to RATE-seq and miRNA-seq to characterize changes in transcription rate and RNA stability.