Developmental Signals - Notch

Introduction

Notch pathway regulation of chondrocyte differentiation and proliferation during appendicular and axial skeleton development

Proc Natl Acad Sci U S A. 2009 Aug 25;106(34):14420-5. Epub 2009 Jul 9.

Mead TJ, Yutzey KE.

Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA. Abstract The role of Notch signaling in cartilage differentiation and maturation in vivo was examined. Conditional Notch pathway gain and loss of function was achieved using a Cre/loxP approach to manipulate Notch signaling in cartilage precursors and chondrocytes of the developing mouse embryo. Conditional overexpression of activated Notch intracellular domain (NICD) in the chondrocyte lineage results in skeletal malformations with decreased cartilage precursor proliferation and inhibited hypertrophic chondrocyte differentiation. Likewise, expression of NICD in cartilage precursors inhibits sclerotome differentiation, resulting in severe axial skeleton abnormalities. Furthermore, conditional loss of Notch signaling via RBP-J gene deletion in the chondrocyte lineage results in increased chondrocyte proliferation and skeletal malformations consistent with the observed increase in hypertrophic chondrocytes. In addition, the Notch pathway inhibits expression of Sox9 and its target genes required for normal chondrogenic cell proliferation and differentiation. Together, our results demonstrate that appropriate Notch pathway signaling is essential for proper chondrocyte progenitor proliferation and for the normal progression of hypertrophic chondrocyte differentiation into bone in the developing appendicular and axial skeletal elements.

PMID: 19590010 http://www.ncbi.nlm.nih.gov/pubmed/19590010

Notch signalling in the paraxial mesoderm is most sensitive to reduced Pofut1 levels during early mouse development

BMC Dev Biol. 2009 Jan 22;9:6.

Schuster-Gossler K, Harris B, Johnson KR, Serth J, Gossler A.

Institute for Molecular Biology, Medizinische Hochschule Hannover, Carl-Neuberg-Str, 1, D-30625, Germany. schuster-gossler.karin@mh-hannover.de Abstract BACKGROUND: The evolutionarily conserved Notch signalling pathway regulates multiple developmental processes in a wide variety of organisms. One critical posttranslational modification of Notch for its function in vivo is the addition of O-linked fucose residues by protein O-fucosyltransferase 1 (POFUT1). In addition, POFUT1 acts as a chaperone and is required for Notch trafficking. Mouse embryos lacking POFUT1 function die with a phenotype indicative of global inactivation of Notch signalling. O-linked fucose residues on Notch can serve as substrates for further sugar modification by Fringe (FNG) proteins. Notch modification by Fringe differently affects the ability of ligands to activate Notch receptors in a context-dependent manner indicating a complex modulation of Notch activity by differential glycosylation. Whether the context-dependent effects of Notch receptor glycosylation by FNG reflect different requirements of distinct developmental processes for O-fucosylation by POFUT1 is unclear.

RESULTS: We have identified and characterized a spontaneous mutation in the mouse Pofut1 gene, referred to as "compact axial skeleton" (cax). Cax carries an insertion of an intracisternal A particle retrotransposon into the fourth intron of the Pofut1 gene and represents a hypomorphic Pofut1 allele that reduces transcription and leads to reduced Notch signalling. Cax mutant embryos have somites of variable size, showed partly abnormal Lfng expression and, consistently defective anterior-posterior somite patterning and axial skeleton development but had virtually no defects in several other Notch-regulated early developmental processes outside the paraxial mesoderm that we analyzed.

CONCLUSION: Notch-dependent processes apparently differ with respect to their requirement for levels of POFUT1. Normal Lfng expression and anterior-posterior somite patterning is highly sensitive to reduced POFUT1 levels in early mammalian embryos, whereas other early Notch-dependent processes such as establishment of left-right asymmetry or neurogenesis are not. Thus, it appears that in the presomitic mesoderm (PSM) Notch signalling is particularly sensitive to POFUT1 levels. Reduced POFUT1 levels might affect Notch trafficking or overall O-fucosylation. Alternatively, reduced O-fucosylation might preferentially affect sites that are substrates for LFNG and thus important for somite formation and patterning.

PMID: 19161597