Deregulated Myt3 translation predisposes islet ß-cells to dysfunction under obesity-induced metabolic stress
In response to obesity-related metabolic stress, islet beta-cells adapt (or compensate) by increasing their secretory function and mass. Yet, for unknown reasons, this compensation is reversed in some individuals at some point to induce beta-cell failure and overt type 2 diabetes. We have previously shown that transcription factor Myt3 (St18) and its paralogs, Myt1 and Myt2, prevent beta-cell failure. Myt3 was induced at post-transcriptional levels by obesity-related stress in both mouse and human beta cells and its downregulation accompanied beta-cell dysfunction during type 2 diabetes development. Single-nucleotide polymorphisms in MYT3 were associated with an increased risk of developing human diabetes. We now demonstrate that Myt3 translation is regulated by an upstream open-reading frame that overlaps with the main Myt3 open-reading frame in mice. Disrupting this overlap enhances Myt3 translation in mouse beta cells without metabolic stress but decreases it under high-fat-diet challenges. Consequently, this deregulation results in beta-cell dysfunction and glucose intolerance in mice, accompanied by compromised expression of several beta-cell function genes, demonstated by sc-RNAseq studies here. These findings suggest that stress-induced Myt3 translation is part of the compensation mechanism that prevents beta-cell failure. Overall design: CRISPR-Cas9-based technique were used to insert 12 bps in one exon of Myt3 (verified by sequencing), which  disrupt an unstream open reading frame. The founder was outcrossed 3 rounds and then used for producing homozygous mice (for WT and mutant alleles). Islets were isolated from these mice for sc-RNAseq.