Long non-coding RNA MCRL1 regulates human cardiac and hematopoietic differentiation via interacting with β-Catenin - PROJECT SUMMARY Mesoderm specification is a critical event at the gastrulation stage of embryogenesis, ultimately giving rise to various mesoderm-derived tissues, including blood and heart. Over the past decades, mechanistic studies on mesoderm specification have predominantly centered on conserved genes, such as transcription factors, epigenetic regulators, and signaling pathways. Particularly, Wnt/β-Catenin pathway critically contributes to the induction of mesodermal cells towards cardiac and hematopoietic fate during gastrulation. However, the existence of human-specific molecular mechanisms underlying mesoderm specification remains enigmatic. Recently, accumulated evidence underscored the essential roles of long non-coding RNAs (lncRNAs) in human cardiovascular development, metabolism, and disease. Using human embryonic stem cells (hESCs) to recapitulate human cardiogenesis, we identified a novel human lncRNA HBL1, which is highly expressed in hESCs and critically regulates human cardiogenesis (Dev Cell 2017,4:333-8; Development 2021.13: dev199628). In this proposal, we discovered another novel human lncRNA termed Mesoderm Commitment Regulatory LncRNA 1 (MCRL1). MCRL1 is a 735bp nuclear lncRNA conserved in non-human primates but absent in rodents. During cardiac differentiation from hESCs, MCRL1 transiently expresses in the mesoderm precisely at the mesoderm specification stage. Notably, MCRL1 deficiency (MCRL1KO) does not affect mesoderm formation, but prominently switches mesoderm specification from cardiac to hematopoietic fate. Transgenic overexpression of MCRL1 in mouse mesoderm leads to embryonic lethality with enlarged heart. Intriguingly, MCRL1 oppositely modulates β-Catenin occupancy on cardiogenic and hematogenic genes. Furthermore, MCRL1-β-Catenin interaction repressed BMI1, a crucial subunit of the PRC1 epigenetic complex. BMI1 ablation in MCRL1KO hESCs restored the aberrant cardiac and hematopoietic commitment from MCRL1KO mesoderm. Thus, we hypothesize that MCRL1 plays a pivotal role in human mesoderm specification towards cardiac and hematopoietic fates by modulating β-Catenin downstream gene expressions at both transcriptional and epigenetic levels. Two specific aims are outlined. Specific Aim 1. Deciphering the transcriptional mechanisms governed by MCRL1-β-Catenin interaction in regulating mesoderm specification. Specific Aim 2. Investigating the epigenetic mechanisms driven by the MCRL1-β-Catenin→BMI1 axis in modulating mesoderm specification.
