Eliminating zebrafish pbx proteins reveals a hindbrain ground state.

The vertebrate hindbrain is divided into serially homologous segments, the rhombomeres (r). Pbx and Hox proteins are hypothesized to form heterodimeric, DNA binding transcription complexes which specify rhombomere identities. Here, we show that eliminating zebrafish Lzr/Pbx4 and Pbx2 function prevents hindbrain segmentation and causes a wholesale anterior homeotic transformation of r2-r6, to r1 identity. We demonstrate that Pbx proteins interact with Hox paralog group 1 proteins to specify segment identities broadly within the hindbrain, and that this process involves the Pbx:Hox-1-dependent induction of Fgf signals in r4. We propose that in the absence of Pbx function, r2-r6 acquire a homogeneous ground state identity, that of r1, and that Pbx proteins, functioning primarily with their Hox partners, function to modify this ground state identity during normal hindbrain development.

[1]  R. Krumlauf,et al.  Cross-regulation in the mouse HoxB complex: the expression of Hoxb2 in rhombomere 4 is regulated by Hoxb1. , 1997, Genes & development.

[2]  A. Lumsden,et al.  Specification of distinct motor neuron identities by the singular activities of individual Hox genes. , 1999, Development.

[3]  R. Krumlauf,et al.  Initiation of Rhombomeric Hoxb4 Expression Requires Induction by Somites and a Retinoid Pathway , 1998, Neuron.

[4]  R. Keynes,et al.  Segmental patterns of neuronal development in the chick hindbrain , 1989, Nature.

[5]  Stephen W. Wilson,et al.  Development of Noradrenergic Neurons in the Zebrafish Hindbrain Requires BMP, FGF8, and the Homeodomain Protein Soulless/Phox2a , 1999, Neuron.

[6]  S. Tapscott,et al.  A conserved motif N-terminal to the DNA-binding domains of myogenic bHLH transcription factors mediates cooperative DNA binding with pbx-Meis1/Prep1. , 1999, Nucleic acids research.

[7]  R. Krumlauf,et al.  Genetic interactions between Hoxa1 and Hoxb1 reveal new roles in regulation of early hindbrain patterning. , 1998, Development.

[8]  A. Waskiewicz,et al.  Zebrafish Meis functions to stabilize Pbx proteins and regulate hindbrain patterning. , 2001, Development.

[9]  K. G. Coleman,et al.  Expression of engrailed proteins in arthropods, annelids, and chordates , 1989, Cell.

[10]  R. Krumlauf,et al.  Segmental expression of Hox-2 homoeobox-containing genes in the developing mouse hindbrain , 1989, Nature.

[11]  I. Mason,et al.  Expression of FGFR1, FGFR2 and FGFR3 during early neural development in the chick embryo , 2000, Mechanisms of Development.

[12]  R. Krumlauf,et al.  The zinc finger gene Krox20 regulates HoxB2 (Hox2.8) during hindbrain segmentation , 1993, Cell.

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

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

[15]  C. Murre,et al.  Engrailed and Hox homeodomain proteins contain a related Pbx interaction motif that recognizes a common structure present in Pbx. , 1996, The EMBO journal.

[16]  P. Chambon,et al.  Hoxa1 and Krox-20 synergize to control the development of rhombomere 3. , 1998, Development.

[17]  S. Vaage.  The segmentation of the primitive neural tube in chick embryos (Gallus domesticus). A morphological, histochemical and autoradiographical investigation. , 1969, Ergebnisse der Anatomie und Entwicklungsgeschichte.

[18]  A. Flenniken,et al.  Segmental expression of the EphA4 (Sek-1) receptor tyrosine kinase in the hindbrain is under direct transcriptional control of Krox-20. , 1998, Development.

[19]  S. Carroll,et al.  Hox repression of a target gene: extradenticle-independent, additive action through multiple monomer binding sites. , 2002, Development.

[20]  R. Krumlauf,et al.  Independent regulation of initiation and maintenance phases of Hoxa3 expression in the vertebrate hindbrain involve auto- and cross-regulatory mechanisms. , 2001, Development.

[21]  Richard S. Mann,et al.  Segmental expression of Hoxb-1 is controlled by a highly conserved autoregulatory loop dependent upon exd/pbx , 1995, Cell.

[22]  I. McGonnell,et al.  Establishment of Hindbrain Segmental Identity Requires Signaling by FGF3 and FGF8 , 2002, Current Biology.

[23]  S. Chanda,et al.  Requirement for Pbx1 in skeletal patterning and programming chondrocyte proliferation and differentiation. , 2001, Development.

[24]  S. Fraser,et al.  Direct imaging of in vivo neuronal migration in the developing cerebellum , 2001, Current Biology.

[25]  N. Hopkins,et al.  vhnf1, the MODY5 and familial GCKD-associated gene, regulates regional specification of the zebrafish gut, pronephros, and hindbrain. , 2001, Genes & development.

[26]  V. Prince,et al.  Knockdown of duplicated zebrafish hoxb1 genes reveals distinct roles in hindbrain patterning and a novel mechanism of duplicate gene retention. , 2002, Development.

[27]  M. Ekker,et al.  fgfr3 and regionalization of anterior neural tube in zebrafish , 2001, Mechanisms of Development.

[28]  R. Mann,et al.  Extra specificity from extradenticle: the partnership between HOX and PBX/EXD homeodomain proteins. , 1996, Trends in genetics : TIG.

[29]  C. Kimmel,et al.  lazarus is a novel pbx gene that globally mediates hox gene function in zebrafish. , 2000, Molecular cell.

[30]  D. Wilkinson,et al.  Function of the Eph-related kinase rtk1 in patterning of the zebrafish forebrain , 1996, Nature.

[31]  M. Capecchi,et al.  Mice mutant for both Hoxa1 and Hoxb1 show extensive remodeling of the hindbrain and defects in craniofacial development. , 1999, Development.

[32]  C. Kimmel,et al.  FGF3 and FGF8 mediate a rhombomere 4 signaling activity in the zebrafish hindbrain. , 2002, Development.

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

[34]  M. Capecchi,et al.  Roles of Hoxa1 and Hoxa2 in patterning the early hindbrain of the mouse. , 2000, Development.

[35]  C. Kimmel,et al.  Stages of embryonic development of the zebrafish , 1995, Developmental dynamics : an official publication of the American Association of Anatomists.

[36]  H Okamoto,et al.  Visualization of Cranial Motor Neurons in Live Transgenic Zebrafish Expressing Green Fluorescent Protein Under the Control of the Islet-1 Promoter/Enhancer , 2000, The Journal of Neuroscience.

[37]  R. Krumlauf,et al.  Cross-regulatory interactions between Hox genes and the control of segmental expression in the vertebrate central nervous system. , 1997, Cold Spring Harbor symposia on quantitative biology.

[38]  M. Westerfield,et al.  Diversity of expression of engrailed-like antigens in zebrafish. , 1991, Development.

[39]  R. Krumlauf,et al.  Segmental expression of Hoxa-2 in the hindbrain is directly regulated by Krox-20. , 1996, Development.

[40]  A. Fritz,et al.  Techniques in neural development. , 1999, Methods in cell biology.

[41]  S. Bonner-Weir,et al.  PDX:PBX complexes are required for normal proliferation of pancreatic cells during development. , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[42]  B. Thisse,et al.  A zebrafish nanos-related gene is essential for the development of primordial germ cells. , 2001, Genes & development.

[43]  R. Krumlauf,et al.  Krox20 and kreisler co‐operate in the transcriptional control of segmental expression of Hoxb3 in the developing hindbrain , 2002, The EMBO journal.