In vertebrate embryos, neural crest cells migrate only through the anterior half of each somite while avoiding the posterior half. We demonstrate that neural crest cells express the receptor neuropilin 2 (Npn2), while its repulsive ligand semaphorin 3F (Sema3f) is restricted to the posterior-half somite. In Npn2 and Sema3f mutant mice, neural crest cells lose their segmental migration pattern and instead migrate as a uniform sheet, although somite polarity itself remains unchanged. Furthermore, Npn2 is cell autonomously required for neural crest cells to avoid Sema3f in vitro. These data show that Npn2/Sema3f signaling guides neural crest migration through the somite. Interestingly, neural crest cells still condense into segmentally arranged dorsal root ganglia in Npn2 nulls, suggesting that segmental neural crest migration and segmentation of the peripheral nervous system are separable processes.KEY WORDS: Trunk neural crest migration, Sclerotome, Neuropilin 2, Semaphorin 3F, Mouse, Chick Development 133, 99-106 doi:10.1242 DEVELOPMENT 100 performed in 50% formamide, 1.3ϫ SSC (pH 5), 5 mM EDTA, 50 g/ml yeast RNA, 0.2% Tween 20, 0.5% CHAPS and 50 g/ml heparin at 70°C. Embryos were washed twice in hybridization mix at 70°C, three times in wash solution I at 65°C, and antibody pre-treatment was performed in 100 mM maleic acid, 150 mM NaCl, 0.1% Tween (pH 7.5) with 2% Blocking Reagent (Boehringer Mannheim). Templates for digoxigenin-labeled antisense riboprobes were as follows: chick Npn2 (Gammill and BronnerFraser, 2002), mouse Npn2 (Giger et al., 2000), Sox10 (Kuhlbrodt et al., 1998), Sema3f (Giger et al., 2000), ephrinB2 (Wang and Anderson, 1997), Tbx18 (Kraus et al., 2001) and Uncx4.1 (Mansouri et al., 1997). Stained embryos were infiltrated with 5% sucrose, 15% sucrose and 7.5% gelatin in 15% sucrose, frozen in liquid nitrogen, sectioned at 20 M by cryostat (Microm) and mounted in permafluor (Thermo Electron Corporation). ImmunohistochemistryNeural crest cells with were stained with 1:50 anti-HNK-1 (American Type Culture; Tucker et al., 1984) followed by 1:400 anti-mouse-IgM-Rhodamine Red X (Jackson Immuno Research) or 1:2000 anti-p75 (Weskamp and Reichardt, 1991) followed by 1:400 anti-rabbit-Rhodamine Red X (Jackson Immuno Research). Sema3f spots were visualized using an anti-mouse IgG Alexa 488 secondary at 1:1000 (Molecular Probes). Unstained embryos were infiltrated with 5% sucrose, 15% sucrose and 7.5% gelatin in 15% sucrose, frozen in liquid nitrogen, sectioned at 15 M by cryostat (Microm) and degelatinized for 20 minutes at 42°C in PBS. Dorsal root ganglia were stained with 1:500 anti-TUJ1 (neuron specific class III ␤-tubulin; Babco) followed by 1:500 anti-mouse-Biotin (Jackson Immuno Research), and developed using the ABC-horseradish peroxidase kit (Vector Laboratories) and 0.1 mg/ml 3,3Ј-diaminobenzidine tetrahydrochloride (DAB; Sigma) with 0.009% hydrogen peroxide according to the manufacturer's instructions. Conditioned medium293T cells were transfected with 24 g of AP-Sema3f (Giger et al., 2000) o...

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The vertebrate neural crest is a migratory stem cell population that arises within the central nervous system. Here, we combine embryological techniques with array technology to describe 83 genes that provide the first gene expression profile of a newly induced neural crest cell. This profile contains numerous novel markers of neural crest precursors and reveals previously unrecognized similarities between neural crest cells and endothelial cells, another migratory cell population. We have performed a secondary screen using in situ hybridization that allows us to extract temporal information and reconstruct the progression of neural crest gene expression as these cells become different from their neighbors and migrate. Our results reveal a sequential 'migration activation' process that reflects stages in the transition to a migratory neural crest cell and suggests that migratory potential is established in a pool of cells from which a subset are activated to migrate.

In the head of vertebrate embryos, neural crest cells migrate from the neural tube into the presumptive facial region and condense to form cranial ganglia and skeletal elements in the branchial arches. We show that newly formed neural folds and migrating neural crest cells express the neuropilin 2 (npn2) receptor in a manner that is highly conserved in amniotes. The repulsive npn2 ligand semaphorin (sema) 3F is expressed in a complementary pattern in the mouse. Furthermore, mice carrying null mutations for either npn2 or sema3F have abnormal cranial neural crest migration. Most notably, \bridges" of migrating cells are observed crossing between neural crest streams entering branchial arches 1 and 2. In addition, trigeminal ganglia fail to form correctly in the mutants and are improperly condensed and loosely organized. These data show that npn2/sema3F signaling is required for proper cranial neural crest development in the head.

Neural crest cell migration is crucial to head and trunk development The neural crest is a migratory, multipotent cell type that forms a vast array of vertebrate structures including the craniofacial skeleton and peripheral nervous system. Abnormalities in the ability of neural crest cells to reach precise target sites cause myriad birth defects. Unraveling the mechanisms that generate neural crest migratory patterns are essential to understanding how molecular signals sculpt the migration, morphogenesis, and differentiation of structures during development. Furthermore, neural crest migration resembles cancer metastasis, and insights into the programmed invasion of a highly migratory cell type may yield clues into the unprogrammed events during cancer. Neural crest cells emerge from the dorsal neural tube (orange line) in a rostrocaudal progression, so that neural crest development is more advanced in the head than in the trunk ("Developmental Age" arrow). Neural crest cells invade surrounding tissues along stereotypical pathways (grey), exhibiting three distinct phases in their migratory behaviors (side bar). This idealized embryo illustrates the patterns, phases, and signals of cranial and trunk neural crest migration in a condensed format.