Non-cell-autonomous control of gastruloid development by the lncRNA T-UCstem1 through DKK1-dependent modulation of WNT signalling

The role and the mechanisms of long non-coding RNA (lncRNAs) in early mammalian embryogenesis remain unclear; this is mostly due to the complexity of the regulatory mechanism of lncRNAs and the limited availability of early embryo samples. The emergence of stem cell-based models of early mammalian embryogenesis offers new opportunities to address these challenging questions. Here we use mouse gastruloids to investigate the role of an ultraconserved lncRNA, T-UCstem1, in the formation of the mammalian body plan. Combining morphological and immunofluorescence analysis with bulk and single cells transcriptomics, we provide unprecedented evidence that T-UCstem1 is a key regulator of gastruloid development and is required for the extension of the anteroposterior axis. Specifically, knock down of T-UCstem1 results in aberrant gastruloid development, which is characterized by altered spatiotemporal expression of the differentiation markers and persistence of pluripotency genes. Single-cell analysis reveals higher cellular heterogeneity in T-UCstem1 KD gastruloids. Notably, the presence of cell populations characterized by the co-expression of pluripotency and differentiation markers points to a key role of T-UCstem1 in establishment and maintenance of proper cellular identity. Mechanistically, we show that T-UCstem1 acts non-cell autonomously through Dickkopf-related protein 1 (DKK-1)-dependent modulation of WNT pathway. Our findings highlight a previously unexplored role for ultraconserved lncRNAs in gastruloid development and open the way for using gastruloids to dissect the functions of lncRNAs in early mammalian development.