Ectopic Hoxa2 induction after neural crest migration results in homeosis of jaw elements in Xenopus.

Hox genes are required to pattern neural crest (NC) derived craniofacial and visceral skeletal structures. However, the temporal requirement of Hox patterning activity is not known. Here, we use an inducible system to establish Hoxa2 activity at distinct NC migratory stages in Xenopus embryos. We uncover stage-specific effects of Hoxa2 gain-of-function suggesting a multistep patterning process for hindbrain NC. Most interestingly, we show that Hoxa2 induction at postmigratory stages results in mirror image homeotic transformation of a subset of jaw elements, normally devoid of Hox expression, towards hyoid morphology. This is the reverse phenotype to that observed in the Hoxa2 knockout. These data demonstrate that the skeletal pattern of rhombomeric mandibular crest is not committed before migration and further implicate Hoxa2 as a true selector of hyoid fate. Moreover, the demonstration that the expression of Hoxa2 alone is sufficient to transform the upper jaw and its joint selectively may have implications for the evolution of jaws.

[1]  J. Clarke,et al.  Stability and plasticity of neural crest patterning and branchial arch Hox code after extensive cephalic crest rotation. , 1998, Developmental biology.

[2]  A. Graham,et al.  Printed in Great Britain © The Company of Biologists Limited 1999 , 1998 .

[3]  R. Mayor,et al.  Induction of the prospective neural crest of Xenopus. , 1995, Development.

[4]  H. Sive,et al.  Efficient hormone-inducible protein function in Xenopus laevis. , 1995, Developmental biology.

[5]  Edoardo Boncinelli,et al.  A distinct Hox code for the branchial region of the vertebrate head , 1991, Nature.

[6]  David G Wilkinson,et al.  Eph receptors and ephrins in neural development , 1999, Current Opinion in Neurobiology.

[7]  V. Prince,et al.  Hoxa-2 expression in normal and transposed rhombomeres: independent regulation in the neural tube and neural crest. , 1994, Development.

[8]  J. Hanken,et al.  Jaw muscle development as evidence for embryonic repatterning in direct–developing frogs , 1997, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[9]  Y. Yan,et al.  Ectopic expression of Hoxa-1 in the zebrafish alters the fate of the mandibular arch neural crest and phenocopies a retinoic acid-induced phenotype. , 1996, Development.

[10]  David G. Wilkinson,et al.  The EphA4 and EphB1 receptor tyrosine kinases and ephrin-B2 ligand regulate targeted migration of branchial neural crest cells , 1997, Current Biology.

[11]  S. Ruffins,et al.  Dorsal hindbrain ablation results in rerouting of neural crest migration and changes in gene expression, but normal hyoid development. , 1997, Development.

[12]  R. Krumlauf,et al.  Hoxa2 and Hoxb2 Control Dorsoventral Patterns of Neuronal Development in the Rostral Hindbrain , 1999, Neuron.

[13]  S. Aizawa,et al.  Development of cephalic neural crest cells in embryos of Lampetra japonica, with special reference to the evolution of the jaw. , 1999, Developmental biology.

[14]  S. Kuratani,et al.  Developmental patterning and evolution of the mammalian viscerocranium: Genetic insights into comparative morphology , 1997, Developmental dynamics : an official publication of the American Association of Anatomists.

[15]  A. Graham,et al.  Segmental origin and migration of neural crest cells in the hindbrain region of the chick embryo. , 1991, Development.

[16]  M. Capecchi,et al.  Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants. , 1999, Development.

[17]  Pierre Chambon,et al.  A homeotic transformation is generated in the rostral branchial region of the head by disruption of Hoxa-2, which acts as a selector gene , 1993, Cell.

[18]  A. Grapin-Botton,et al.  The regeneration of the cephalic neural crest, a problem revisited: the regenerating cells originate from the contralateral or from the anterior and posterior neural fold. , 1996, Development.

[19]  A. Grapin-Botton,et al.  Determination of the identity of the derivatives of the cephalic neural crest: incompatibility between Hox gene expression and lower jaw development. , 1998, Development.

[20]  J. Greer,et al.  Maintenance of functional equivalence during paralogous Hox gene evolution , 2000, Nature.

[21]  P. Chambon,et al.  Role of Hoxa-2 in axon pathfinding and rostral hindbrain patterning. , 1997, Development.

[22]  E. D. De Robertis,et al.  Duplicated homeobox genes in Xenopus. , 1989, Developmental biology.

[23]  D M Noden,et al.  The role of the neural crest in patterning of avian cranial skeletal, connective, and muscle tissues. , 1983, Developmental biology.

[24]  J. Postlethwait,et al.  Ectopic expression of hoxb2 after retinoic acid treatment or mRNA injection: Disruption of hindbrain and craniofacial morphogenesis in zebrafish embryos , 1998, Developmental dynamics : an official publication of the American Association of Anatomists.

[25]  A. Lumsden,et al.  Rhombencephalic neural crest segmentation is preserved throughout craniofacial ontogeny. , 1996, Development.

[26]  J. Langeland,et al.  Otx expression during lamprey embryogenesis provides insights into the evolution of the vertebrate head and jaw. , 1999, Developmental biology.

[27]  P. Helbling,et al.  Requirement for EphA receptor signaling in the segregation of Xenopus third and fourth arch neural crest cells , 1998, Mechanisms of Development.

[28]  N M Le Douarin,et al.  The triple origin of skull in higher vertebrates: a study in quail-chick chimeras. , 1993, Development.

[29]  S. Fraser,et al.  Segmental migration of the hindbrain neural crest does not arise from its segmental generation. , 1993, Development.

[30]  Moisés Mallo,et al.  Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest , 1993, Cell.

[31]  M. Mallo,et al.  Hoxa-2 restricts the chondrogenic domain and inhibits bone formation during development of the branchial area. , 1998, Development.

[32]  F. Mavilio,et al.  Functional dissection of a transcriptionally active, target‐specific Hox–Pbx complex , 1997, The EMBO journal.

[33]  P. Krieg,et al.  Xbap, a vertebrate gene related to bagpipe, is expressed in developing craniofacial structures and in anterior gut muscle. , 1997, Developmental biology.

[34]  S. J. Marcus,et al.  Developmental regulation of transcription factor AP-2 during Xenopus laevis embryogenesis , 1991, Nucleic Acids Res..

[35]  S. Fraser,et al.  Segmentation in the chick embryo hindbrain is defined by cell lineage restrictions , 1990, Nature.

[36]  R. Ho,et al.  Zebrafish hox genes: expression in the hindbrain region of wild-type and mutants of the segmentation gene, valentino. , 1998, Development.

[37]  R. Harland,et al.  In situ hybridization: an improved whole-mount method for Xenopus embryos. , 1991, Methods in cell biology.

[38]  P. Chambon,et al.  The expression pattern of the mouse receptor tyrosine kinase gene MDK1 is conserved through evolution and requires Hoxa-2 for rhombomere-specific expression in mouse embryos. , 1996, Developmental biology.

[39]  B. Hall.  Evolutionary issues in craniofacial biology. , 1990, The Cleft palate journal.

[40]  M Manzanares,et al.  Regulation of Hoxa2 in cranial neural crest cells involves members of the AP-2 family. , 1999, Development.

[41]  D M Noden,et al.  Patterning of avian craniofacial muscles. , 1986, Developmental biology.

[42]  M Nirenberg,et al.  Murine Hox-1.11 homeobox gene structure and expression. , 1992, Proceedings of the National Academy of Sciences of the United States of America.

[43]  H. Ruley,et al.  An Enhancer Element in the EphA2 (Eck) Gene Sufficient for Rhombomere-specific Expression Is Activated by HOXA1 and HOXB1 Homeobox Proteins* , 1998, The Journal of Biological Chemistry.

[44]  M. Castagna,et al.  Distribution and cellular localization of the serotonin type 2C receptor messenger RNA in human brain , 1999, Neuroscience.

[45]  B. Sadaghiani,et al.  Neural crest development in the Xenopus laevis embryo, studied by interspecific transplantation and scanning electron microscopy. , 1987, Developmental biology.

[46]  R. Krumlauf,et al.  Rhombomere of origin determines autonomous versus environmentally regulated expression of Hoxa-3 in the avian embryo. , 1996, Development.

[47]  P. Forey,et al.  Agnathans and the origin of jawed vertebrates , 1993, Nature.

[48]  P. Sharpe,et al.  Temporospatial cell interactions regulating mandibular and maxillary arch patterning. , 2000, Development.