show Abstracthide AbstractLncRNAs are developmentally regulated and highly cell type-specific non-coding RNAs that have emerged as important regulators of cell fate commitment and maintenance. In this study, we dissected the role of lncRNAs in human pancreas development by classifying lncRNAs based on their dynamic regulation, subcellular localization, and engagement with ribosomes during the stepwise differentiation of human embryonic stem cells (hESCs) towards pancreatic fate. We then deleted 10 candidate lncRNAs in hESCs and characterized the knockout phenotypes of pancreatic developmental intermediates, prioritizing dynamically regulated lncRNAs with validated translation potential and proximity to developmental TFs. This small-scale loss-of-function screen revealed that most lncRNAs are dispensable for pancreatic development and the regulation of nearby genes. We identify LINC00261 as the first translated lncRNA involved in human endocrine cell development, and show that it regulates gene expression in pancreatic progenitor cells in trans rather than cis. Through systematic dissection of LINC00261's coding and noncoding functions, we can exclude a role for the produced micropeptides in this process. Instead, we posit that, over the course of pancreatic differentiation, the biological activity of multiple lncRNAs is controlled by a regulatory, translation machinery dependent mechanism that employs ribosome engagement and short open reading frame translation to dose lncRNA activity in the nucleus. It is conceivable that inadequate nuclear LINC00261 dosage during human pancreas development could predispose individuals to developing diabetes. Overall design: RNA-seq and Ribo-seq analysis of H1 embryonic stem cells differentiated towards the pancreatic endocrine cell fate.