Neural crest defects in ephrin-B2 mutant mice are non-autonomous and originate from defects in the vasculature

Abstract

Ephrin-B2, a member of the Eph/ephrin family of cell signaling molecules, has been implicated in the guidance of cranial and trunk neural crest cells (NCC) and development of the branchial arches(BA), but detailed examination in mice has been hindered by embryonic lethality of Efnb2 null loss of function due to a requirement in angiogenic remodeling. To elucidate the developmental roles for Efnb2, we generated a conditional rescue knock-in allele that allows rescue of ephrin-B2 specifically in the vascular endothelium (VE), but is otherwise ephrin-B2 deficient. Restoration of ephrin-B2 expression specifically to the VE completely circumvents angiogenic phenotypes, indicating that the requirement of ephrin-B2 in angiogenesis is limited to the VE. Surprisingly, we find that expression of ephrin-B2 specifically in the VE is also sufficient for normal NCC migration and that conversely, embryos in which ephrin-B2 is absent specifically from the VE exhibit NCC migration and survival defects. Disruption of vascular development independent of loss of ephrin-B2 function also leads to defects in NCC and BA development. Together, these data indicate that direct ephrin-B2 signaling to NCCs is not required for NCC guidance, which instead depends on proper organization of the embryonic vasculature.

Angiopoietin 2 signaling plays a critical role in neural crest cell migration

“…Furthermore, Ang2 has been studied for its role in destabilizing endothelial cell junctions, and in the presence of VEGF or other growth factors, it can induce sprouting of disassembled endothelial cells [15, 44, 45]. Previous static analyses in mouse [46] and chick [4, 47] hinted at a potential dynamic interplay between migrating neural crest and endothelial cells during head patterning. By combining cell labeling, molecular perturbation, and time-lapse microscopy within a Tie1:H2B-YFP transgenic quail embryo, we were able to address our hypothesis and describe novel aspects about the spatio-temporal dynamics of neural crest and endothelial cells in the same embryo.…”

EphrinB2-EphB4-RASA1 Signaling in Human Cerebrovascular Development and Disease

“…Conditional mouse knockout of ephrinB2 specifically in the endothelium and endocardium of the developing vasculature and heart (ephrinB2 lacZ/loxP ; Tie2-Cre + ) showed angiogenic remodeling defects [20] identical to those seen in global ephrinB2 knockout mice [20,21], indicating that sufficient expression of ephrinB2 in endothelial and endocardial cells is required for angiogenesis and that the expression of ephrinB2 in surrounding mesenchymal cells and mural cells, including pericytes (PCs) and vascular smooth muscle cells (vSMCs), cannot compensate for the loss of ephrinB2 in vascular cells [20]. Furthermore, restoration of ephrinB2 expression specifically in vascular ECs of Efnb2 null mice (Eftib2 CR/GFP ; Tie2-Cre Tg/+ ) was able to completely rescue defects in angiogenesis, suggesting the role of ephrinB2 for normal angiogenesis is restricted to vascular ECs [22], even though failure of rescuing cardiovascular defects in Efnb2 null mice by ECs specific ephrinB2 restoration (Efnb2 GFP/GFP ; T g ) possibly due to insufficient ephrinB2 level was also reported [23]. However, conditional mouse knockout of ephrinB2 in mural cells (Efnb2 ΔPC/vSMC ) resulted in perinatal lethality and caused edema and extensive hemorrhaging in the skin in addition to vascular defects in a range of organs [24] due to the scatter and loose attachment of PCs and vSMCs to the micro-vessels, suggesting a role of ephrinB2 in mediating interactions between mural cells as well as between PCs and the endothelium.…”

Cellular organization and boundary formation in craniofacial development

“…The fact that EphA4 and ephrin‐B2‐expressing cells come into contact in the hindbrain and during early NCC migration, but are separated during migration into the arches, suggests that the NCC segmentation function of Eph/ephrin signaling occurs early; to what extent these functions may be related to even earlier disruption of rhombomere boundaries is not clear, but the fact that overexpression of ephrin‐B2 can lead to a variety of redirections of the NCCs indicates that Eph/ephrin signaling is capable of redirecting NCCs relatively late in their migration. Though loss of function of ephrin‐B2 in mice also results in disruption of NCC development and a hypoplastic second branchial arch, this phenotype is attributable to a role for ephrin‐B2 within the vascular endothelium for NCC survival rather than migratory guidance (Davy & Soriano, ; Lewis, Hwa, Wang, Soriano, & Bush, ). It is possible that redundancy in function may explain the lack of an obvious guidance phenotype in ephrin‐B2 loss of function models.…”