...-restricted units called rhombomeres. Loss-of-function mutants and ectopic expression assays reveal that Hoxb4 and its paralogue Hoxd4 are necessary and sufficient for cell segregation, and for the most caudal rhombomere boundary (r6/r7). Hox4 proteins regulate Eph/ephrins and other cell-surface proteins...

...Isaac Skromne; Dean Thorsen; Melina Hale; Victoria E. Prince; Robert K. Ho The spinal cord is a unique vertebrate feature that originates, together with the hindbrain, from the caudal neural plate. Whereas the hindbrain subdivides into rhombomeres, the spinal cord remains unsegmented. We have...

... the anteroposterior (AP) axis. Like neural crest cells and motoneurons, first-order sensory relay interneurons also require specification along the AP axis. Hox genes are prime candidates for providing this information. In support of this hypothesis, we show that distinct combinations of Hox genes in rhombomeres (r...

... of the hindbrain; formation of otocysts, pharyngeal arches and forelimb buds; and in the closure of the primitive gut. The hindbrain of E8.5 Aα/Aγ embryos shows a posterior expansion of rhombomere 3 and 4 (R3 and R4) markers, but fails to express kreisler , a normal marker of R5 and R6. This abnormal hindbrain...

... preferentially reduced in size during development. Specification of the midbrain region and of the rostralmost rhombomeres is apparently normal in the absence of RA synthesis. In contrast, marked alterations are seen throughout the caudal hindbrain of mutant embryos. Instead of being expressed in two alternate...

... , genes that encode signaling molecules thought to be key components of the mid/hindbrain (isthmic) organizer. In the absence of Gbx2 function, isthmic nuclei, the cerebellum, motor nerve V, and other derivatives of rhombomeres 1-3 fail to form. Additionally, the posterior midbrain in the mutant embryos...

...Ronald Nittenberg; Ketan Patel; Yogish Joshi; Robb Krumlauf; David G. Wilkinson; Paul M. Brickell; Cheryll Tickle; Jonathan D. W. Clarke ABSTRACT Rhombomeres are segmental units of the hindbrain that are separated from each other by a specialised zone of boundary cells. Retinoic acid application...

...Anne Grapin-Botton; Marie-Ange Bonnin; Nicole M. Le Douarin ABSTRACT It has been previously shown that Hox gene expression in the rhombencephalon is controlled by environmental cues. Thus posterior transposition of anterior rhombomeres to the r7/8 level results in the activation of Hox genes...

.... We find that this enhancer plays an important role in the early establishment of the Hoxa-1 anterior expression boundary in the neural plate. This early disturbance in Hoxa-1 activation results in rhombomere and cranial nerve abnormalities reminiscent of those obtained in the Hoxa-1 total knockout...

... single rhombomere, by means of the quail-chick chimera technique. Expression of certain Hox genes ( Hoxa-2, Hoxa-3 and Hoxb-4 ) was recorded in the branchial arches of chick and quail embryos at embryonic days 3 (E3) and E4. This was a pre-requisite for studying the regeneration capacities of the neural...

... connectivity was found that precisely respects the positional origin of its constitutive crest: each rhombomeric population remains coherent throughout ontogeny, forming both the connective tissues of specific muscles and their respective attachment sites onto the neuro- and viscerocranium. Finally, focal...

...Christiane Niederländer; Andrew Lumsden ABSTRACT Morphological segmentation of the avian hindbrain into rhombomeres is also reflected by the emergent organisation of branchiomotor nerves. In each case, the motor neurons of these nerves lie in two adjacent rhombomeres (e.g. of the Vth nerve in r2...

... (e-mail: [email protected] ) 19 03 1996 © 1996 by Company of Biologists 1996 forebrain midbrain hindbrain rhombomeres dorsoventral patterning cyclops axial pax-2 hlx-1 The establishment of the dorsoventral axis of the neural plate is one...

...Stefan Nonchev; Christine Vesque; Mark Maconochie; Tania Seitanidou; Linda Ariza-McNaughton; Monique Frain; Heather Marshall; Mai Har Sham; Robb Krumlauf; Patrick Charnay ABSTRACT The hindbrain is a segmented structure divided into repeating metameric units termed rhombomeres (r). The Hox family...

...Anne Grapin-Botton; Marie-Ange Bonnin; Linda Ariza McNaughton; Robb Krumlauf; Nicole M. Le Douarin ABSTRACT In this study we have analysed the expression of Hoxb-4, Hoxb-1, Hoxa-3, Hoxb-3, Hoxa-4 and Hoxd-4 in the neural tube of chick and quail embryos after rhombomere (r) heterotopic...

... to day 8.25). Exposure to RA prior to the onset of somitic segmentation results in suppression of rhombomeric (but not somitic) segmentation, and conversion of the genetic identity of the whole preotic hindbrain to that of rhombomere 4. In contrast, exposure to RA at early somite stages results in near...

... possible phenotypes. These single-phenotype clones were not positionally restricted within a rhombomere but were interspersed with other clones containing distinct phenotypes. The assignment of neuronal phenotype in this brain region may, therefore, be made in early precursors and remembered through...

...Victoria Prince; Andrew Lumsden ABSTRACT In this study we have cloned the chick Hoxa-2 gene and analysed its expression during early development. We find that Hoxa-2 has a rostral limit of expression in the rhombencephalic neural tube corresponding precisely to the boundary between rhombomeres (r)1...

.... Lufkin, A. Dierich, M. LeMeur, M. Mark and P. Chambon, 1991; Cell 66, 1105-1119). Three-dimensional reconstructions of the Hoxa-1 −/− rhombencephalon reveals that it bears only five rhombomeric structures (ie. morphological segments) instead of the normal seven. The first three of these rhombomeres...

...Anthony Graham; Isobel Heyman; Andrew Lumsden ABSTRACT Neural crest cells originate at three discontinuous levels along the rostrocaudal axis of the chick rhomben-cephalon, centred on rhombomeres 1 and 2, 4 and 6, respectively. These are separated by the odd-numbered rhombomeres r3 and r5 which...