Notch signaling regulates left–right asymmetry determination by inducingNodalexpression

Abstract

Generation of left-right asymmetry is an integral partGeneration of left-right asymmetry during development is an integral part of the establishment of the vertebrate body plan (Capdevila et al. 2000;Mercola and Levin 2001;Wright 2001;Yost 2001;Hamada et al. 2002). Specification of the left-right axis requires multiple steps: (1) generation of an initial asymmetric signal in or near the embryonic node, (2) transfer of asymmetric signals from the node to the lateral plate mesoderm (LPM), (3) induction of an evolutionarily conserved cascade of gene expression in the left LPM, and (4) transformation of these left-right asymmetric signals into morphological asymmetries of the visceral organs. In mice, generation of the initial asymmetric signal requires directional fluid flow on the ventral surface of the node (Nonaka et al. 2002). This fluid flow is generated by motile monocilia on cells of the node, and the presence of nodal cilia is conserved in other vertebrates (Essner et al. 2002). However, the mechanism by which directional fluid flow at the node specifies orientation of the left-right axis is controversial (Stern and Wolpert 2002;Tabin and Vogan 2003). In addition, the mechanism for transfer of the initial asymmetric signal from the node to the LPM is unknown.The Notch signaling pathway is an evolutionarily conserved intercellular signaling mechanism. Mutations in Notch pathway components disrupt embryonic development in diverse multicellular organisms and cause in- Here we demonstrate that the Notch signaling pathway plays a primary role in the establishment of leftright asymmetry in mice by directly regulating expression of the Nodal gene. Embryos mutant for the Notch ligand Dll1 or doubly mutant for the Notch1 and Notch2 receptors exhibit multiple defects in left-right asymmetry. Notably, Dll1 −/− embryos do not express Nodal in the region around the node. Analysis of the enhancer regulating node-specific Nodal expression (termed the NDE) revealed the presence of binding sites for the RBP-J protein. Mutation of these sites destroyed the ability of the NDE to direct node-specific gene expression in transgenic mice. These results demonstrate that Dll1-mediated Notch signaling is essential for generation of leftright asymmetry, and indicate that perinodal expression of the Nodal gene is an essential component of left-right asymmetry determination in mice. Results and Discussion Laterality defects in Dll1 mutant and Notch1/Notch2 double-mutant mouse embryosDuring studies on the role of the Dll1 gene during somitogenesis (Zhang et al. 2002), we observed that some Dll1 −/− embryos (Hrabé de Angelis et al. 1997) exhibited reversed heart looping. We examined this phenotype more closely by performing scanning electron micros-

Laterality defects are influenced by timing of treatments and animal model

“…A considerable number of studies have reported complete absence of nodal, lefty, or pitx2 expression (Field et al, 2011; Oki et al, 2010; Sakano et al, 2010; Gaio et al, 1999; Takeuchi et al, 2007; Zhang et al, 2001; Yan et al, 1999; Tsukui et al, 1999; Collignon et al, 1996; Kramer-Zucker et al, 2005; Krebs et al, 2003; Pennekamp et al, 2002), with some reporting 100% absent expression for all three genes. What does complete absence of gene expression mean?…”

Three types of cilia including a novel 9+4 axoneme on the notochordal plate of the rabbit embryo

“…The primary embryonic organizer, Spemann's organizer in the amphibian embryo, Hensen's node in rabbit and mouse, and the embryonic shield in the teleost fish embryo, from which the dorsal forerunner cells and hence Kupffer's vesicle (KV) are derived, thus sets the stage for the development of the PNC/GRP/KV or its equivalent in other vertebrates, which func-tionally may turn out to be primarily involved in LR axis development. Experimental manipulation of the organizer thus affects all three body axes, while defects in PNC/GRP/KV cause laterality defects without affecting the main body axes (Herrmann and Kispert, 1994;Nonaka et al, 1998;Krebs et al, 2003;Przemeck et al, 2003;Abdelkhalek et al, 2004).…”

NOTCH activation interferes with cell fate specification in the gastrulating mouse embryo

“…In the post-implantation epiblast at E5.5, Nodal expression is controlled by pluripotency factors, and notably by OCT4 and by an auto-regulatory loop involving NODAL signalling (Adachi et al, 1999;Norris et al, 2002;Norris and Robertson, 1999). In addition, WNT3/β-catenin signalling triggers Nodal upregulation in the E6.5 posterior epiblast and primitive streak (Ben-Haim et al, 2006;Vincent et al, 2003), and NOTCH/RBPJ signalling controls its expression in the node from E7.5 (Krebs et al, 2003;Raya et al, 2003). The ectopic anterior expression of Nodal observed in E7.5 N1ICD epi embryos might result from a direct action of N1ICD/ RBPJ on the Nodal node-specific enhancer (NDE) (Adachi et al, 1999;Krebs et al, 2003;Norris and Robertson, 1999; Raya et al, 2003).…”