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D G Wilkinson

Publications and source records attributed to D G Wilkinson.

At least 55 records · Page 3Linked to original sources
PubMed1996

Progressive spatial restriction of Sek-1 and Krox-20 gene expression during hindbrain segmentation.

After segmentation of the vertebrate hindbrain, expression of the zinc-finger gene Krox-20 and the receptor tyrosine kinase gene Sek-1 is precisely restricted to rhombomeres (r) 3 and 5. This precise segmental expression is likely to reflect a critical requirement for these rhombomeres to acquire a distinct and homogeneous identity and raises the question as to how this relates to the intermingling and restriction of cell movement during segmentation. We have analysed Krox-20 and Sek-1 expression in the mouse and chick hindbrain at single-cell resolution using whole-mount in situ hybridisation and immunocytochemistry. We find that, in the mouse, the presumptive r3 and r5 expression domains each arise as narrow stripes that then broaden, suggestive of a recruitment of cells to an r3/r5 identity and/or a segmental regulation of cell proliferation. In addition, we find that expression of these genes initially occurs in fuzzy domains, and that these are progressively restricted to segmental domains, although occasional "violating" cells are observed even after segmentation. We propose that the establishment and maintenance of these segmental domains may involve both a dynamic regulation of r3/r5 identity and the restriction of cell movement across rhombomere boundaries.

Animals↗
PubMed1996

Expression and regulation of Cek-8, a cell to cell signalling receptor in developing chick limb buds.

The Eph-related receptor tyrosine kinase gene, Cek-8, is expressed in mesenchyme at the tip of chick limb buds, with high levels of transcripts posteriorly and apically but fading out anteriorly. Expression of Cek-8 in distal mesenchyme is regulated by apical ridge- and FGF-polarising signals and retinoic acid, and is uniform across the anteroposterior axis in talpid3 mutants. These data indicate that Cek-8 expression responds to regulatory signals during limb patterning and suggest that this receptor tyrosine kinase may have a role in coordinating responses to signals in the progress zone of early buds. Later on in limb development, Cek-8 expression is associated with cell condensations that form tendons and their attachments to cartilage rudiments and then in developing feather buds.

Animals↗
PubMed1996

Cell-cell interactions and segmentation in the developing vertebrate hindbrain.

During development of the vertebrate hindbrain, regulatory gene expression becomes precisely restricted to specific segments. Studies at the cellular and molecular levels suggest that establishment of this precise pattern of gene expression may involve a dynamic regulation of cell identity and a restriction of cell movement across rhombomere boundaries. Candidates for mediating such interactions are several members of the Eph-related receptor tyrosine kinase (RTK) family that have segmental expression in the hindbrain. Ligands for members of this RTK family are membrane-bound, and may therefore mediate cell contact-dependent signalling. We discuss the expression patterns of Eph-related receptors in the hindbrain and the potential roles that these may play in patterning.

Animals↗
PubMed1995

Relationship between spatially restricted Krox-20 gene expression in branchial neural crest and segmentation in the chick embryo hindbrain.

Previous studies have suggested that the rostrocaudal patterning of branchial arches in the vertebrate embryo derives from a coordinate segmental specification of gene expression in rhombomeres (r) and neural crest. However, expression of the Krox-20 gene is restricted to neural crest cells migrating to the third branchial arch, apparently from r5, whereas this rhombomere contributes cells to both the second and third arches. We examined in the chick embryo how this spatially restricted expression is established. Expression occurs in precursors in both r5 and r6, and we show by cell labelling that both rhombomeres contribute to Krox-20-expressing neural crest, emigration occurring first from r6 and later caudally from r5. Krox-20 transcripts are not detected in some precursors in rostral r5, presaging the lack of expression in cells migrating rostrally from this rhombomere. After transposition of r6 to the position of r4 or r5, many Krox-20-expressing cells migrate rostral to the otic vesicle, whereas when r5 is transplanted to the position of r4, only a small number of migrating cells express Krox-20. These results indicate that, in the chick, Krox-20 expression in branchial neural crest does not correlate with rhombomeric segmentation, and that there may be intrinsic differences in regulation between the r5 and r6 Krox-20-expressing populations.

Animals↗
PubMed1995

Cloning, sequencing, and expressional analysis of the chick homologue of follistatin.

Follistatin, a secreted glycoprotein, has been shown to act as a potent neural inducer during early amphibian development. The function of this protein during embryogenesis in higher vertebrates is unclear, and to further our understanding of its role we have cloned, sequenced, and performed an in-depth expressional analysis of the chick homologue of follistatin. In addition we also describe the expression pattern of activin beta A and activin beta B, proteins that have previously been shown to be able to interact with follistatin. In this study we show that the expression of follistatin and the activins do not always overlap. Follistatin was first detected in Hensen's node and subsequently in the region described by Spratt [1952] as the neuralising area. In older embryos it was also expressed in a highly dynamic manner in the hindbrain as well as in the somites. We also present evidence that follistatin may have a later role in the resegmentation of the somites. We were unable to detect the expression of activin beta A during early embryogenesis, whereas activin beta B was first expressed in the extending primitive streak and subsequently in the neural folds. The results from this study are consistent with a role for follistatin in neural induction but suggest it has additional functions unrelated to its inhibitory actions on activins.

Activins↗
PubMed1995

Murine Wnt-11 and Wnt-12 have temporally and spatially restricted expression patterns during embryonic development.

The Wnt gene family encodes a set of signalling molecules implicated in the development of a wide range of organisms. We have recently cloned partial cDNA sequences of murine Wnt-11 and Wnt-12. Here, we describe the spatio-temporal expression patterns of both genes during mouse embryogenesis. Wnt-11 expression is first detected within the truncus arteriosus from 8.25 dpc. By 9.5 dpc, Wnt-11 expression is detected in the somites at the medial junction of the dermatome and the myotome. Wnt-11 transcripts are also detected in limb bud mesenchyme from the time the bud is first visible. Wnt-12 is detected in the apical ectodermal ridge from 10.5 dpc. The implications of these expression patterns are discussed.

Amino Acid Sequence↗
PubMed1995

RNA detection using non-radioactive in situ hybridization.

Methods of non-radioactive in situ hybridization to RNA now enable the simultaneous detection of two RNAs in the same tissue. Sensitivity has been increased by several modifications, including the use of the polymerase chain reaction. Recently, in situ hybridization has been combined with lineage tracing to determine the origin of cells expressing a specific gene.

Animals↗
PubMed1995

Expression of truncated Sek-1 receptor tyrosine kinase disrupts the segmental restriction of gene expression in the Xenopus and zebrafish hindbrain.

During development of the vertebrate hindbrain regulatory gene expression is confined to precise segmental domains. Studies of cell lineage and gene expression suggest that establishment of these domains may involve a dynamic regulation of cell identity and restriction of cell movement between segments. We have taken a dominant negative approach to interfere with the function of Sek-1, a member of the Eph-related receptor tyrosine kinase family expressed in rhombomeres r3 and r5. In Xenopus and zebrafish embryos expressing truncated Sek-1, lacking kinase sequences, expression of r3/r5 markers occurs in adjacent even-numbered rhombomeres, in domains contiguous with r3 or r5. This disruption is rescued by full-length Sek-1, indicating a requirement for the kinase domain in the segmental restriction of gene expression. These data suggest that Sek-1, perhaps with other Eph-related receptors, is required for interactions that regulate the segmental identity or movement of cells.

Amino Acid Sequence↗
PubMed1995

Genetic control of segmentation in the vertebrate hindbrain.

Studies of cell commitment and gene expression suggest that the subdivision of the hindbrain into segments and the specification of their anteroposterior identity emerges from a prepattern in the early neural plate. This prepattern imposes a regional specification, but not a commitment of individual cells to specific segments, and may involve the spatial expression of the Krox-20 and Hox genes. The generation of null mutants has shown that the Krox-20 gene is required for the formation of definitive r3 and r5, and the Hoxa-1 gene is required for r4 and r5 development. A mouse mutant, kreisler, has disrupted hindbrain segmentation, with r5 and r6 failing to form. Studies of gene expression in these mutants suggest that the kreisler gene has an early role, whereas the Krox-20 and Hoxa-1 genes have later roles in the formation of definitive segments. I propose that a community effect of cell-cell signaling may underlie the commitment of cells to specific segments and discuss the implications of this for the phenotype of segmentation mutants. The receptor tyrosine kinases encoded by the Sek-1, Sek-2, Sek-3, and Sek-4 genes are segmentally expressed and could mediate cell-cell interactions that regulate cell commitment and hindbrain segmentation.

Animals↗
PubMed1994

Control of cell behavior during vertebrate development by Slug, a zinc finger gene.

Slug, a vertebrate gene encoding a zinc finger protein of the Snail family, is expressed in the neural crest and in mesodermal cells emigrating from the primitive streak. Early chick embryos were incubated with antisense oligonucleotides to chick Slug. These oligonucleotides specifically inhibit the normal change in cell behavior that occurs at the two sites in the emerging body plan in which the gene is expressed. This change, which is the transition from epithelial to mesenchymal character, occurs at the formation of mesoderm during gastrulation and on emigration of the neutral crest from the neural tube.

Amino Acid Sequence↗
PubMed1994

Several receptor tyrosine kinase genes of the Eph family are segmentally expressed in the developing hindbrain.

Pattern formation in the hindbrain involves a segmentation process leading to the formation of metameric units, manifested as successive swellings known as rhombomeres (r). In search for genes involved in cell-cell interactions during hindbrain segmentation, we have screened for protein kinase genes with restricted expression patterns in this region of the CNS. We present the cloning of three novel mouse genes, Sek-2, Sek-3 and Sek-4 (members of the Eph subfamily of putative transmembrane receptor protein tyrosine kinases (RTKs)), the identification of their chromosomal locations, and the analysis of their expression between 7.5 and 10.5 days of development. Before morphological segmentation, Sek-2 is transcribed in a transverse stripe corresponding to prospective r4 and the adjacent mesoderm, suggesting possible roles both in hindbrain segmentation and signalling between neuroepithelium and mesoderm. Sek-3 and Sek-4 have common domains of expression, including r3, r5 and part of the midbrain, as well as specific domains in the diencephalon, telencephalon, spinal cord and in mesodermal and neural crest derivatives. Together with our previous finding that Sek (Sek-1) is expressed in r3 and r5 (Gilardi-Hebenstreit et al., 1992; Nieto et al., 1992), these data indicate that members of the Eph family of RTKs may co-operate in the segmental patterning of the hindbrain.

Amino Acid Sequence↗
PubMed1993

Molecular mechanisms of segmental patterning in the vertebrate hindbrain and neural crest.

Recent work has shown that segmentation underlies the patterning of the vertebrate hindbrain and its neural crest derivatives. Several genes have been identified with segment-restricted expression, and evidence is now emerging regarding their function and regulatory relationships. The expression patterns of Hox genes and the phenotype of null mutants indicate roles in specifying segment identity. A zinc finger gene Krox-20 is a segment-specific regulator of Hox expression, and it seems probable that retinoic acid receptors also regulate Hox genes in the hindbrain. The receptor tyrosine kinase gene Sek may mediate cell-cell interactions that lead to segmentation. These studies provide a starting point for understanding the molecular basis of segmental patterning in the hindbrain.

Animals↗
PubMed1993

The structure and expression of the Xenopus Krox-20 gene: conserved and divergent patterns of expression in rhombomeres and neural crest.

Recent studies in the chick have indicated that rhombomeres (r) are segments that underlie the patterning of hindbrain nerves. These segments may also be important for the specification of branchial arch structures since alternating rhombomeres, r2, r4 and r6, each contribute crest to a specific arch. Krox-20 has been implicated in the segmental patterning of the hindbrain in the mouse by its expression prior to segment formation in alternating domains, which later correspond to r3 and r5. Here, we describe the sequence and developmental expression of the Xenopus Krox-20 gene, XKrox-20. Alternating domains of XKrox-20 expression appear in the early neurula, later correspond to r3 and r5, and persist until late tadpole stages. In contrast to this conserved spatial expression in rhombomeres, we find a pattern in the neural crest of Xenopus that appears different from that found in the mouse: expression occurs in crest that migrates from r5 into the third visceral arch. We speculate that this may reflect a distinct route of neural crest migration due to anatomical differences between these systems, rather than a difference in the site of origin of Krox-20-expressing crest.

Amino Acid Sequence↗
PubMed1993

Molecular mechanisms of segmental patterning in the vertebrate hindbrain.

The finding that pattern formation in the vertebrate hindbrain occurs through a process of segmentation raises the question of the underlying molecular mechanisms. A number of genes have been implicated in this pattern through their segment-restricted expression, and the function and possible regulatory relationships of these are discussed. There is now strong evidence that certain Hox genes are involved in specifying hindbrain segments and neural crest derivatives that contribute to cranial ganglia and the branchial arches. It is likely that retinoic acid receptors either directly or indirectly regulate Hox gene expression in the hindbrain. The zinc finger gene Krox-20 controls the segment-restricted up-regulation of at least one Hox gene, Hox-B2. Studies of the Krox-20 gene reveal a progressive sharpening of its expression domains that reflect cellular interactions leading to segment formation. A receptor tyrosine kinase gene, Sek, has been implicated in such cellular interactions by its rhombomeric expression pattern. In addition, this receptor kinase may be involved in mesoderm segmentation.

Animals↗
PubMed1992

Molecular mechanisms of pattern formation in the vertebrate hindbrain.

During early stages of neural development a series of repeated bulges, termed rhombomeres, form in the vertebrate hindbrain. Studies in the chick have shown that rhombomeres are segments that underlie the patterning of nerves in the hindbrain, and this raises the question of the molecular basis of segment development. Several genes have been found with expression patterns consistent with roles in the formation or differentiation of rhombomeres. The zinc finger gene Krox-20 is expressed in two alternating rhombomeres, r3 and r5, in the mouse hindbrain; these stripes of gene expression are established prior to the morphological appearance of segments. Krox-20 is also expressed in this pattern in the chick and Xenopus, suggesting that it has a conserved role, possibly in the formation of rhombomeres. Four members of the Hox-2 homeobox gene cluster have limits of expression at rhombomere boundaries. Three genes, Hox-2.6, -2.7 and -2.8 have progressively more anterior limits of expression at two-segment intervals, whereas expression of Hox-2.9 is restricted to one rhombomere, r4. The Hox-2 genes are expressed in spatially restricted patterns in early neural crest cells. These findings suggest that the Hox genes have roles in specifying the identity of rhombomeres and of neural crest.

Animals↗