Regulation of intrathymic T‐cell development by Lunatic Fringe– Notch1 interactions

Abstract

Intrathymic Notch1 signaling critically regulates T-lineage specification and commitment as well as T-cell progenitor survival and differentiation. Notch1 activation is continuously required during progression of early CD4/CD8-double-negative thymocytes to the CD4/CD8-double-positive stage. This developmental transition occurs as thymocytes migrate from the corticomedullary junction (CMJ) to the outer subcapsular zone (SCZ) of the thymus. Members of two families of structurally distinct Notch ligands, Delta-like 1 and Jagged-1, are expressed by cortical thymic epithelial cells, but it is not known which ligands are functionally required within the CMJ and SCZ microenvironmental niches. Our laboratory has investigated this question by genetically manipulating thymocyte expression of Lunatic Fringe (L-Fng), a glycosyltransferase that enhances sensitivity of Notch receptors to Delta-like ligands. This approach has revealed that low-threshold intrathymic Notch1 signals instruct multipotent thymus-seeding progenitors to suppress their B-cell potential and choose the T-cell fate. This strategy has also revealed that Delta-like Notch ligands are functionally limiting in both the CMJ and SCZ microenvironmental niches. Finally, we discuss our recent demonstration that L-Fng-mediated competition for Delta-like ligands is an important mechanism for regulating thymus size.

Protein O-fucosyltransferase 1 (Pofut1) regulates lymphoid and myeloid homeostasis through modulation of Notch receptor ligand interactions

“…In this context, Lfng promotes progenitor competition for limited thymic niches in an environment populated by more abundant DP thymocytes that express much lower levels of Lfng. 43 Similarly, both Lfng and Manic Fringe (Mfng) expressed in newly formed B cells and MZB cell precursors cooperatively enhance the binding of Dll1 with Notch2 and thus promote MZB-cell development. 14 Our transplantation studies and coculture of Pofut1-deleted LSK with OP9-Dll4 cells identify a critical role for Pofut1-regulated Notch signaling in both T-and MZB-cell development.…”

TheO-fucose glycan in the ligand-binding domain of Notch1 regulates embryogenesis and T cell development

“…Competition experiments using Notch1 ϩ/Ϫ heterozygous cells show that the level of Notch1 signaling must be regulated for optimal T cell development to occur (35,36). This is presumably why enhancing Notch1 signaling by overexpression of Notch1 intracellular domain (NICD) has led to several different proposals on the role of Notch1 signaling in the DP-to-SP transition Ratios of SP/DP and CD4/CD8 subsets were calculated.…”

Regulation of Notch signaling by glycosylation

“…In addition, elimination of a glycosyltransferase may have pleiotrophic consequences if it has more than one function, or it acts in both a cell-autonomous and non cell-autonomous fashion [13][14][15]. Overexpression artefacts are a concern when transgenes are expressed under the control of exogenous promoters and/or in an ectopic location, since regulated Notch signaling is notoriously sensitive to the level of Notch receptor activity [46,47]. Drosophila has one Fringe while mammals have three (Lfng, Mfng and Rfng).…”

“…Mutations of Fringe give Notch signaling defects that manifest at developmental boundaries in the formation of wings, legs and eyes in Drosophila [7]. In mammals, including humans [48], Lfng is required for Notch signaling during somitogenesis, and affects female meiosis [49] and T cell development in mice [47]. In vivo functions of Rfng are not noticeably developmental [10] and Mfng mutant mice have not been described.…”