Core clock gene BMAL1 and RNA-binding protein MEX3A collaboratively regulate Lgr5 expression in intestinal crypt cells
Li-Tzu Cheng, Grace Y.T. Tan, Fang‐Pei Chang, Cheng‐Kai Wang, Yu‐Chi Chou, Pang‐Hung Hsu, Wendy W. Hwang‐Verslues
Abstract
Abstract The intestinal epithelium is highly regenerative. Rapidly proliferating LGR5 + crypt base columnar (CBC) cells are responsible for epithelial turnover needed to maintain intestinal homeostasis. Upon tissue damage, loss of LGR5 + CBCs can be compensated by activation of quiescent +4 intestinal stem cells (ISCs) or early progenitor cells to restore intestinal regeneration. LGR5 + CBC self-renewal and ISC conversion to LGR5 + cells are regulated by external signals originating from the ISC niche. In contrast, little is known about intrinsic regulatory mechanisms critical for maintenance of LGR5 + CBC homeostasis. We found that LGR5 expression in intestinal crypt cells is controlled by the circadian core clock gene BMAL1 and the BMAL1-regulated RNA-binding protein MEX3A. BMAL1 directly activated transcription of Mex3a . MEX3A in turn bound to and stabilized Lgr5 mRNA. Bmal1 depletion reduced Mex3a and Lgr5 expression and led to increased ferroptosis, which consequently decreased LGR5 + CBC numbers and increased the number of crypt cells expressing +4 ISC marker BMI1. Together, these findings reveal a BMAL1-centered intrinsic regulatory pathway that maintains LGR5 expression in the crypt cells and suggest a potential mechanism contributing to ISC homeostasis.