ABSTRACT
During the development of forebrain connectivity, ascending thalamocortical and descending corticofugal axons first intermingle at the pallial-subpallial boundary to form the internal capsule (IC). However, the identity of molecular cues that guide these axons remains largely unknown. Here, we show that the transmembrane protein Linx is robustly expressed in the prethalamus and lateral ganglionic eminence-derived corridor and on corticofugal axons, but not on thalamocortical axons, and that mice with a null mutation of Linx exhibit a complete absence of the IC. Moreover, regional inactivation of Linx either in the prethalamus and LGE or in the neocortex leads to a failure of IC formation. Furthermore, Linx binds to thalamocortical projections, and it promotes outgrowth of thalamic axons. Thus, Linx guides the extension of thalamocortical axons in the ventral forebrain, and subsequently, it mediates reciprocal interactions between thalamocortical and corticofugal axons to form the IC.
Subject(s)
Axons/metabolism , Internal Capsule/metabolism , Nerve Tissue Proteins/physiology , Prosencephalon/physiology , Thalamus/physiology , Animals , Axons/physiology , Internal Capsule/physiology , Mice , Mice, Inbred C57BL , Mice, Knockout , Nerve Tissue Proteins/deficiency , Neural Pathways/physiology , Organ Culture Techniques , Protein Binding/physiologyABSTRACT
The development of a patterned vasculature is essential for normal organogenesis. We found that signaling by semaphorin 3E (Sema3E) and its receptor plexin-D1 controls endothelial cell positioning and the patterning of the developing vasculature in the mouse. Sema3E is highly expressed in developing somites, where it acts as a repulsive cue for plexin-D1-expressing endothelial cells of adjacent intersomitic vessels. Sema3E-plexin-D1 signaling did not require neuropilins, which were previously presumed to be obligate Sema3 coreceptors. Moreover, genetic ablation of Sema3E or plexin-D1 but not neuropilin-mediated Sema3 signaling disrupted vascular patterning. These findings reveal an unexpected semaphorin signaling pathway and define a mechanism for controlling vascular patterning.
Subject(s)
Blood Vessels/embryology , Glycoproteins/metabolism , Membrane Glycoproteins/metabolism , Membrane Proteins/metabolism , Nerve Tissue Proteins/metabolism , Somites/metabolism , Animals , Binding Sites , Blood Vessels/metabolism , Body Patterning , COS Cells , Chick Embryo , Chlorocebus aethiops , Cytoskeletal Proteins , Endothelial Cells/cytology , Endothelial Cells/physiology , Endothelium, Vascular/cytology , Endothelium, Vascular/embryology , In Situ Hybridization , Intracellular Signaling Peptides and Proteins , Ligands , Mice , Morphogenesis , Mutation , Neuropilin-1/metabolism , Neuropilin-2/metabolism , Phenotype , Protein Binding , Recombinant Fusion Proteins/metabolism , Semaphorins , Signal Transduction , TransfectionABSTRACT
Neuropilin-1 (Npn-1) is a receptor that binds multiple ligands from structurally distinct families, including secreted semaphorins (Sema) and vascular endothelial growth factors (VEGF). We generated npn-1 knockin mice, which express an altered ligand binding site variant of Npn-1, and npn-1 conditional null mice to establish the cell-type- and ligand specificity of Npn-1 function in the developing cardiovascular and nervous systems. Our results show that VEGF-Npn-1 signaling in endothelial cells is required for angiogenesis. In striking contrast, Sema-Npn-1 signaling is not essential for general vascular development but is required for axonal pathfinding by several populations of neurons in the CNS and PNS. Remarkably, both Sema-Npn-1 signaling and VEGF-Npn-1 signaling are critical for heart development. Therefore, Npn-1 is a multifunctional receptor that mediates the activities of structurally distinct ligands during development of the heart, vasculature, and nervous system.
