Maqueda, M. | Search bioRxiv

bioRxiv2023

Radical fringe facilitates NOTCH1 and JAG1 cis interactions to sustain Hematopoietic stem cell fate

Hematopoietic stem cells (HSCs) develop within a short time window from the hemogenic endothelium in the aorta- gonads-and mesonephros (AGM) region during embryonic development. The first HSCs reside within Intra-aortic hematopoietic clusters (IAHC) along with hematopoietic progenitors (HPC). The signalling mechanisms that divert HSCs from HPCs are unknown. Notch signaling is essential for arterial specification, IAHC formation and HSC activity, but current studies on how Notch drives these different fates are inconsistent. To determine the role of Notch in the specification of hemogenic endothelium, HSC and/or HPCs, we extensively analyzed Notch dynamics in the period of HSC generation. We defined the expression pattern of Notch signalling molecules at the gene and protein level and established a molecular mechanism that reconcile previous studies demonstrating the loss of HSC activity in NOTCH1, JAG1 and RBPJ null mutants, the enhanced HSC generation by blocking specific Notch activities or the abrogation of emerging HSCs by high Notch activation. We now demonstrate that Notch activity is highest in a subset of Gfi1+ hemogenic endothelial cells and is gradually lost with HSC maturation. We uncover that the HSC phenotype is maintained through loss of Notch activity due to increasing levels of NOTCH1 and JAG1 interactions on the surface of the same cell (cis) that renders the NOTCH1 receptor from being activated. Forcing activation of the NOTCH1 receptor in IAHC cells activates a hematopoietic differentiation program and supports a cis-inhibitory function for JAG1 and NOTCH1. Furthermore, we demonstrate that this cis-inhibitory interaction is enabled by RADICAL FRINGE (RFNG), a glycosyltransferase that enhances the affinity of NOTCH1 to JAG1 in cis. Finally, our results indicate that NOTCH1-JAG1 cis-inhibition is necessary for preserving the HSC phenotype in the hematopoietic clusters of the aorta.

developmental biology↗

bioRxiv2021

The transcriptional repressor REST is a major negative regulator of endocrine differentiation during pancreas organogenesis

Understanding genomic regulatory mechanisms of pancreas differentiation is relevant to the pathophysiology of diabetes mellitus, and to the development of replacement therapies. Numerous transcription factors promote {beta} cell differentiation, although less is known about negative regulators. Earlier epigenomic studies suggested that the transcriptional repressor REST could be a suppressor of endocrine gene programs in the embryonic pancreas. However, pancreatic Rest knock-out mice failed to show increased numbers of endocrine cells, suggesting that REST is not a major regulator of endocrine differentiation. Using a different conditional allele that enables profound REST inactivation, we now observe a marked increase in the formation of pancreatic endocrine cells. REST inhibition also promoted endocrinogenesis in zebrafish and mouse early postnatal ducts, and induced {beta}-cell specific genes in human adult duct-derived organoids. Finally, we define REST genomic programs that suppress pancreatic endocrine differentiation. These results establish a crucial role of REST as a negative regulator of pancreatic endocrine differentiation.

developmental biology↗