1: Dev Cell. 2005 Feb;8(2):179-92. The transcriptional control of trunk neural crest induction, survival, and delamination. Cheung M, Chaboissier MC, Mynett A, Hirst E, Schedl A, Briscoe J. Developmental Neurobiology, National Institute for Medical Research, Mill Hill, London, NW7 1AA, UK. Trunk neural crest cells are generated at the border between the neural plate and nonneural ectoderm, where they initiate a distinct program of gene expression, undergo an epithelial-mesenchymal transition (EMT), and delaminate from the neuroepithelium. Here, we provide evidence that members of three families of transcription induce these properties in premigratory neural crest cells. Sox9 acts to provide the competence for neural crest cells to undergo an EMT and is required for trunk neural crest survival. In the absence of Sox9, cells apoptose prior to or shortly after delamination. Slug/Snail, in the presence of Sox9, is sufficient to induce an EMT in neural epithelial cells, while FoxD3 regulates the expression of cell-cell adhesion molecules required for neural crest migration. Together, the data suggest a model in which a combination of transcription factors regulates the acquisition of the diverse properties of neural crest cells. PMID: 15691760 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 2: Development. 2005 Mar;132(5):1069-83. Epub 2005 Feb 2. A pair of Sox: distinct and overlapping functions of zebrafish sox9 co-orthologs in craniofacial and pectoral fin development. Yan YL, Willoughby J, Liu D, Crump JG, Wilson C, Miller CT, Singer A, Kimmel C, Westerfield M, Postlethwait JH. Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA. Understanding how developmental systems evolve after genome amplification is important for discerning the origins of vertebrate novelties, including neural crest, placodes, cartilage and bone. Sox9 is important for the development of these features, and zebrafish has two co-orthologs of tetrapod SOX9 stemming from an ancient genome duplication event in the lineage of ray-fin fish. We have used a genotype-driven screen to isolate a mutation deleting sox9b function, and investigated its phenotype and genetic interactions with a sox9a null mutation. Analysis of mutant phenotypes strongly supports the interpretation that ancestral gene functions partitioned spatially and temporally between Sox9 co-orthologs. Distinct subsets of the craniofacial skeleton, otic placode and pectoral appendage express each gene, and are defective in each single mutant. The double mutant phenotype is additive or synergistic. Ears are somewhat reduced in each single mutant but are mostly absent in the double mutant. Loss-of-function animals from mutations and morpholino injections, and gain-of-function animals injected with sox9a and sox9b mRNAs showed that sox9 helps regulate other early crest genes, including foxd3, sox10, snai1b and crestin, as well as the cartilage gene col2a1 and the bone gene runx2a; however, tfap2a was nearly unchanged in mutants. Chondrocytes failed to stack in sox9a mutants, failed to attain proper numbers in sox9b mutants and failed in both morphogenetic processes in double mutants. Pleiotropy can cause mutations in single copy tetrapod genes, such as Sox9, to block development early and obscure later gene functions. By contrast, subfunction partitioning between zebrafish co-orthologs of tetrapod genes, such as sox9a and sox9b, can relax pleiotropy and reveal both early and late developmental gene functions. PMID: 15689370 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 3: Development. 2004 Nov;131(21):5327-39. Epub 2004 Sep 29. Canonical Wnt activity regulates trunk neural crest delamination linking BMP/noggin signaling with G1/S transition. Burstyn-Cohen T, Stanleigh J, Sela-Donenfeld D, Kalcheim C. Department of Anatomy and Cell Biology, Hebrew University-Hadassah Medical School, PO Box 12272, Jerusalem 91120, Israel. Delamination of premigratory neural crest cells depends on a balance between BMP/noggin and on successful G1/S transition. Here, we report that BMP regulates G1/S transition and consequent crest delamination through canonical Wnt signaling. Noggin overexpression inhibits G1/S transition and blocking G1/S abrogates BMP-induced delamination; moreover, transcription of Wnt1 is stimulated by BMP and by the developing somites, which concomitantly inhibit noggin production. Interfering with beta-catenin and LEF/TCF inhibits G1/S transition, neural crest delamination and transcription of various BMP-dependent genes, which include Cad6B, Pax3 and Msx1, but not that of Slug, Sox9 or FoxD3. Hence, we propose that developing somites inhibit noggin transcription in the dorsal tube, resulting in activation of BMP and consequent Wnt1 production. Canonical Wnt signaling in turn stimulates G1/S transition and generation of neural crest cell motility independently of its proposed role in earlier neural crest specification. PMID: 15456730 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 4: Development. 2004 Sep;131(18):4455-65. Epub 2004 Aug 11. LSox5 regulates RhoB expression in the neural tube and promotes generation of the neural crest. Perez-Alcala S, Nieto MA, Barbas JA. Instituto Cajal CSIC, Doctor Arce 37, 28002 Madrid, Spain. Members of the Sox family of transcription factors are involved in a number of crucial developmental processes, including sex determination, neurogenesis and skeletal development. LSox5 is a member of the group D Sox factors that, in conjunction with Sox6 and Sox9, promotes chondrogenesis by activating the expression of cartilage-specific extracellular matrix molecules. We have cloned the chicken homologue of LSox5 and found that it is initially expressed in the premigratory and migratory neural crest after Slug and FoxD3. Subsequently, the expression of LSox5 is maintained in cephalic crest derivatives, and it appears to be required for the development of the glial lineage, the Schwann cells and satellite glia in cranial ganglia. Misexpression of LSox5 in the cephalic neural tube activated RhoB expression throughout the dorsoventral axis. Furthermore, the prolonged forced expression of LSox5 enlarged the dorsal territory in which the neural crest is generated, extended the 'temporal window' of neural crest segregation, and led to an overproduction of neural crest cells in cephalic regions. In addition to HNK-1, the additional neural crest cells expressed putative upstream markers (Slug, FoxD3) indicating that a regulatory feedback mechanism may operate during neural crest generation. Thus, our data show that in addition to the SoxE genes (Sox9 and Sox10) a SoxD gene (Sox5) also participates in neural crest development and that a cooperative interaction may operate during neural crest generation, as seen during the formation of cartilage. PMID: 15306568 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 5: Development. 2003 Jul;130(14):3111-24. Neural crest induction by paraxial mesoderm in Xenopus embryos requires FGF signals. Monsoro-Burq AH, Fletcher RB, Harland RM. Department of Molecular and Cellular Biology, University of California at Berkeley, CA 94720, USA. monsoro@uclink.berkeley.edu At the border of the neural plate, the induction of the neural crest can be achieved by interactions with the epidermis, or with the underlying mesoderm. Wnt signals are required for the inducing activity of the epidermis in chick and amphibian embryos. Here, we analyze the molecular mechanisms of neural crest induction by the mesoderm in Xenopus embryos. Using a recombination assay, we show that prospective paraxial mesoderm induces a panel of neural crest markers (Slug, FoxD3, Zic5 and Sox9), whereas the future axial mesoderm only induces a subset of these genes. This induction is blocked by a dominant negative (dn) form of FGFR1. However, neither dnFGFR4a nor inhibition of Wnt signaling prevents neural crest induction in this system. Among the FGFs, FGF8 is strongly expressed by the paraxial mesoderm. FGF8 is sufficient to induce the neural crest markers FoxD3, Sox9 and Zic5 transiently in the animal cap assay. In vivo, FGF8 injections also expand the Slug expression domain. This suggests that FGF8 can initiate neural crest formation and cooperates with other DLMZ-derived factors to maintain and complete neural crest induction. In contrast to Wnts, eFGF or bFGF, FGF8 elicits neural crest induction in the absence of mesoderm induction and without a requirement for BMP antagonists. In vivo, it is difficult to dissociate the roles of FGF and WNT factors in mesoderm induction and neural patterning. We show that, in most cases, effects on neural crest formation were parallel to altered mesoderm or neural development. However, neural and neural crest patterning can be dissociated experimentally using different dominant-negative manipulations: while Nfz8 blocks both posterior neural plate formation and neural crest formation, dnFGFR4a blocks neural patterning without blocking neural crest formation. These results suggest that different signal transduction mechanisms may be used in neural crest induction, and anteroposterior neural patterning. PMID: 12783784 [PubMed - indexed for MEDLINE] ---------------------------------------------------------------