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C Tickle

Publications and source records attributed to C Tickle.

At least 73 records · Page 4Linked to original sources
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

Activation of Fgf-4 and HoxD gene expression by BMP-2 expressing cells in the developing chick limb.

Bone morphogenetic protein-2 (BMP-2) has been implicated in the polarizing region signalling pathway, which specifies pattern across the antero-posterior of the developing vertebrate limb. Retinoic acid and Sonic Hedgehog (SHH) can act as polarizing signals; when applied anteriorly in the limb bud, they induce mirror-image digit duplications and ectopic Bmp-2 expression in anterior mesenchyme. In addition, the two signals can activate Fgf-4 expression in anterior ridge and HoxD expression in anterior mesenchyme. We tested the role of BMP-2 in this signalling cascade by ectopically expressing human BMP-2 (hBMP-2) at the anterior margin of the early wing bud using a replication defective retroviral vector, and found that ectopic expression of Fgf-4 was induced in the anterior part of the apical ectodermal ridge, followed later by ectopic expression of Hoxd-11 and Hoxd-13 in anterior mesenchyme. This suggests that BMP-2 is involved in regulating Fgf-4 and HoxD gene expression in the normal limb bud. Ectopically expressed hBMP-2 also induced duplication of digit 2 and bifurcation of digit 3, but could not produce the mirror-image digit duplications obtained with SHH-expressing cells. These results suggest that BMP-2 may be involved primarily in maintenance of the ridge, and in the link between patterning and outgrowth of the limb bud.

Animals↗
PubMed1995

Fibroblast growth factors induce additional limb development from the flank of chick embryos.

Fibroblast growth factors (FGFs) act as signals in the developing limb and can maintain proliferation of limb bud mesenchyme cells. Remarkably, beads soaked in FGF-1, FGF-2, or FGF-4 and placed in the presumptive flank of chick embryos induce formation of ectopic limb buds, which can develop into complete limbs. The entire flank can produce additional limbs, but generally wings are formed anteriorly and legs posteriorly. FGF application activates Sonic hedgehog in cells with polarizing potential to make a discrete polarizing region. Hoxd-13 is also expressed in the ectopic bud, and an apical ectodermal ridge forms. A limb bud is thus established that can generate the appropriate signals to develop into a complete limb. The additional limbs have reversed polarity. This can be explained by the distribution of cells in the flank with potential polarizing activity. The results suggest that local production of an FGF may initiate limb development.

Animals↗
PubMed1995

Expression of genes encoding bone morphogenetic proteins and sonic hedgehog in talpid (ta3) limb buds: their relationships in the signalling cascade involved in limb patterning.

The chicken mutant talpid3 (ta3) has polydactylous limbs with up to 7-8 morphologically similar digits. This lack of antero-posterior polarity in digit pattern is correlated with symmetrical expression of genes of the HoxD complex. We determined the distribution of polarizing activity in limb buds of the chick mutant ta3 by assessing the ability of mesenchyme from various positions along the antero-posterior axis to induce digit duplications when grafted anteriorly into a normal limb. Cells with highest polarizing activity were found at the posterior margin of the wing as in the polarizing region of normal limb buds. However, in contrast to normal limb buds, ta3 anterior mesenchyme also had low polarizing activity. Application of retinoic acid or a polarizing region graft to the anterior of ta3 limb buds changed digit morphology but did not induce digit duplications or digits with any characteristic a-p pattern. To determine which genes are associated with polarizing activity and which are associated with patterning of the digits, we examined expression of the genes Sonic hedgehog (shh), Bmp-2, and Bmp-7, whose expression is normally confined to the posterior margin of the early wing bud and is associated with the polarizing region. In addition, we determined the distribution of Fgf-4 transcripts which in normal limb buds are restricted to the posterior part of the apical ectodermal ridge. In ta3 limb buds, shh expression is restricted to the posterior limb mesenchyme, which has high polarizing activity, but is not expressed in regions which have low polarizing activity. In contrast, Bmp-2 and Bmp-7 are expressed uniformly along the a-p axis. Fgf-4 transcripts are present throughout the apical ectodermal ridge in ta3 limb buds. In the ta3 mutant, there is both an abnormal distribution of signalling activity and response to polarizing signals. In addition, the dissociation between the expression of shh and Bmps suggests distinct roles for the encoded molecules in signalling and response in a-p patterning of limb buds.

Animals↗
PubMed1995

Gnot1, a member of a new homeobox gene subfamily, is expressed in a dynamic, region-specific domain along the proximodistal axis of the developing limb.

Limb development endures as an excellent model for pattern formation in vertebrates. We have identified Gnot1 as a member of a new homeobox gene subfamily. Gnot1 is expressed in a dynamic temporospatial distribution in the developing limb, initially correlating with regions destined to form distal structures and then becoming progressively more restricted to specific regions determined to give rise to wrist and ankle. Micro-surgical alteration of the developmental program of the limb reveals that Gnot1 is expressed in a position- and fate-dependent manner, responding both to signals from the apical ridge and the polarizing zone. Furthermore, Gnot1 activation by polarizing signals occurs temporally downstream of Hoxd gene activation, but well before the first appearance of condensations that will give rise to the carpus of the wrist. The features of Gnot1 expression suggest a role for this gene in regulating pattern formation during limb development.

Age Factors↗
PubMed1995

Vertebrate limb development.

The recent identification of Wnt-7a as a signalling molecule in dorsal/ventral patterning means that we now have a known signal for control of each of the three limb axes. Fibroblast growth factors can allow proximal/distal patterning and Sonic hedgehog gene expression signals anterior/posterior patterning. Networks of these signals not only coordinate cell responses, but also mutually maintain each other. A positive feedback loop is established which coordinates expression of Sonic hedgehog in mesenchyme cells of the polarizing region and Fgf-4 expression in overlying apical ridge ectoderm. Wnt-7a expression in dorsal ectoderm also influences Sonic hedgehog expression in the polarizing region. Initiation of development of a complete limb can be achieved with just one signal, a growth factor.

Animals↗
PubMed1994

A positive feedback loop coordinates growth and patterning in the vertebrate limb.

Limb development depends on signals from the apical ectodermal ridge and underlying mesenchyme. Fibroblast growth factor (FGF) can replace the ridge and, because Fgf4 RNA is localized to the mouse posterior ridge, we proposed that FGF4 is the endogenous ridge signal. Ridge signals control limb outgrowth and maintain the zone of polarizing activity (ZPA) at the limb posterior margin, which is important in limb pattering: a ZPA graft to limb anterior mesenchyme causes cell respecification and mirror-image duplications. Sonic hedgehog (SHH) has polarizing activity, and Shh RNA co-localizes with ZPA activity, suggesting SHH is the endogenous polarizing signal. We have investigated the molecular regulation of Fgf4 and Shh expression. We report here that Fgf4 expression in the ridge can be regulated by Shh-expressing cells. Moreover, Shh expression in mesenchyme can be activated by FGF4 in combination with retinoic acid. Once induced, Shh expression can be maintained by FGF4 alone, thus establishing a positive feedback loop between ZPA and ridge.

Amino Acid Sequence↗
PubMed1994

Function of FGF-4 in limb development.

The apical ectodermal ridge plays a central role in limb development through its interactions with the underlying mesenchyme. Removal of the AER results in cessation of limb outgrowth and leads to truncation of the limb along the proximo-distal axis. The many functions attributed to the ridge include maintenance of the progress zone mesenchyme. Here, cells are stimulated to proliferate, are maintained in an undifferentiated state, and are assigned progressively more distal positional values as the limb grows. The AER also functions to maintain the activity of the polarizing region, a region of mesenchyme which is thought to provide the primary signal for patterning along the antero-posterior axis. We have begun to explore the function of fibroblast growth factor-4 (FGF-4) during limb development. FGF-4, which encodes an efficiently secreted protein, is expressed in the AER. We have previously demonstrated that FGF-4 protein can stimulate limb mesenchyme proliferation and can induce the expression of a downstream homeobox gene, Evx-1 (homologue of the Drosophila even-skipped gene), that is normally regulated by a signal from the AER. To determine to what extent FGF-4 protein can substitute for the AER to allow normal limb outgrowth, we performed experiments on the developing chick limb in ovo. Remarkably, we find that after AER removal, the FGF-4 protein can provide all the signals required for virtually normal outgrowth and patterning of the limb.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Expression of the connexin43 gap junctional protein in tissues at the tip of the chick limb bud is related to the epithelial-mesenchymal interactions that mediate morphogenesis.

The pattern of connexin43 expression in developing chick limb buds was examined using a site-specific polyclonal antibody and confocal microscopy. Connexin43 is expressed at stages of limb development when epithelial-mesenchymal interactions are occurring that mediate morphogenesis. Extensive labeling was observed in the apical ectodermal ridge and labeling was also found in underlying mesenchyme cells at the tip of the bud. In mouse limb buds, the same gap junction protein is expressed only in the apical ridge. Manipulations of developing chick wing buds show that mesenchymal expression of connexin43 appears to be controlled by the apical ectodermal ridge. When the apical ridge is surgically removed and limb truncations result, mesenchymal labeling is markedly reduced and conversely the grafting of an additional ridge induces connexin43 expression between underlying mesenchymal cells which do not normally show expression at this stage of development. In addition, a treatment with retinoic acid that flattens the apical ridge and inhibits bud outgrowth reduces expression in both mesenchymal and epithelial tissues. The abolition of connexin43 expression in mesenchymal and epithelial domains when bud outgrowth is halted suggests that synthesis of this gap junction protein is related to the epithelial-mesenchymal interactions that mediate morphogenesis of the bud.

Animals↗
PubMed1994

Bone morphogenetic proteins and a signalling pathway that controls patterning in the developing chick limb.

We show here that bone morphogenetic protein 2 (BMP-2) is involved in patterning the developing chick limb. During early stages of limb development, mesenchymal expression of the Bmp-2 gene is restricted to the posterior part of the bud, in a domain that colocalizes with the polarizing region. The polarizing region is a group of cells at the posterior margin of the limb bud that can respecify the anteroposterior axis of the limb when grafted anteriorly and can activate expression of genes of the HoxD complex. We dissect possible roles of BMP-2 in the polarizing region signalling pathway by manipulating the developing wing bud. Retinoic acid application, which mimics the effects of polarizing region grafts, activates Bmp-2 gene expression in anterior cells. This shows that changes in anteroposterior pattern are correlated with changes in Bmp-2 expression. When polarizing region grafts are placed at the anterior margin of the wing bud, the grafts continue to express the Bmp-2 gene and also activate Bmp-2 expression in the adjacent anterior host mesenchyme. These data suggest that BMP-2 is part of the response pathway to the polarizing signal, rather than being the signal itself. In support of this, BMP-2 protein does not appear to have any detectable polarizing activity when applied to the wing bud. The pattern of Bmp-4 gene expression in the developing wing bud raises the possibility that BMP-2 and BMP-4 could act in concert. There is a close relationship, both temporal and spatial, between the activation of the Bmp-2 and Hoxd-13 genes in response to retinoic acid and polarizing region grafts, suggesting that expression of the two genes might be linked.

Amino Acid Sequence↗
PubMed1994

Tissue and cellular patterning of the musculature in chick wings.

Development of the musculature involves generation of a precise number of individual muscles arranged in appropriate locations, each with the correct cellular patterning. To find out the rules that govern muscle number and arrangement, the forearm musculature of chick wing buds was analysed following grafts of the polarizing region or application of retinoic acid. Muscle patterns appear symmetrical with 'posterior' muscles now forming in the anterior part of the wing. When the number of muscles that develop is reduced, pattern symmetry is maintained, with loss of anterior muscles in the mid-line, especially dorsally. Strict anteroposterior ordering of muscles in duplicated patterns does not always occur. The number of muscles that develops bears some relationship to the number of forearm elements. Each muscle has a characteristic pattern of fast and slow fibres. In duplicated wings, each pair of symmetrically arranged muscles has the same fibre type pattern. Not only are proportions of fast and slow fibres similar, but local variations in fibre type arrangement within the muscle are also reproduced. This suggests that the cellular pattern within the new 'posterior' muscles at the anterior of the limb has been re-specified. In manipulated limb buds, which will develop a duplicated muscle pattern, there are no detectable changes in distribution and number of potentially myogenic cells, and fibre type patterning within early muscle masses also appears normal. In contrast, the splitting process that divides up muscle masses is altered. The appropriate fibre type arrangement only emerges after splitting is complete. This suggests that tissue patterning and cellular patterning occur at different times during muscle development.

Animals↗
PubMed1993

FGF-4 replaces the apical ectodermal ridge and directs outgrowth and patterning of the limb.

The apical ectodermal ridge plays a key role in limb development. We show that recombinant FGF-4 can substitute for the ridge to provide all the signals necessary for virtually complete outgrowth and patterning of the chick limb. FGF-4 stimulates proliferation of cells in the distal mesenchyme and maintains a signal from the posterior to the distal mesenchyme that appears to be required for elaboration of skeletal elements in the normal proximodistal sequence. Moreover, retinoic acid, which is capable of providing polarizing activity, can supply this signal. This suggests that polarizing activity plays a role in patterning along the proximodistal axis, in addition to its well-established role in anteroposterior patterning. Taken together, the data suggest a simple mechanism whereby FGF-4 links growth and pattern formation during limb development.

Animals↗
PubMed1993

Syndactylies and polydactylies: embryological overview and suggested classification.

In 1978, Temtamy and McKusick classified isolated, non-syndromic polydactyly and syndactyly, using a logical anatomical approach, into five distinct types for each group. Since then, there have been considerable advances in the molecular embryology of the developing limb bud. These include the proposal that retinoic acid and/or related retinoids are the morphogens responsible for the morphogenetic gradient giving rise to anterior-posterior pattern formation of the limb bud, the suggestion that the HOX4 complex and other homeotic genes may also be involved in patterning, and a greater understanding of other mechanisms such as programmed cell death in the shaping of the final hand and foot. This paper briefly reviews the molecular embryology of limb development and outlines the 'end-organ responsiveness' of the limbs to a variety of single-gene mutations. An alternative classification of syndactylies and polydactylies is suggested. It is still too early to match specific defects to individual genes with precision, and it is obvious that many important developmental genes remain to be identified; nevertheless, it is envisaged that clues from molecular embryological studies will become increasingly more useful.

Animals↗
PubMed1993

FGF-4 maintains polarizing activity of posterior limb bud cells in vivo and in vitro.

The polarizing region is a major signalling tissue involved in patterning the tissues of the vertebrate limb. The polarizing region is located at the posterior margin of the limb bud and can be recognized by its ability to induce additional digits when grafted to the anterior margin of a chick limb bud. The signal from the polarizing region operates at the tip of the bud in the progress zone, a zone of undifferentiated mesenchymal cells, maintained by interactions with the apical ectodermal ridge. A number of observations have pointed to a link between the apical ectodermal ridge and signalling by the polarizing region. To test this possibility, we removed the posterior apical ectodermal ridge of chick wing buds and assayed posterior mesenchyme for polarizing activity. When the apical ectodermal ridge is removed, there is a marked decrease in polarizing activity of posterior cells. The posterior apical ectodermal ridge is known to express FGF-4 and we show that the decrease in polarizing activity of posterior cells of wing buds that normally follows ridge removal can be prevented by implanting a FGF-4-soaked bead. Furthermore, we show that both ectoderm and FGF-4 maintain polarizing activity of limb bud cells in culture.

Animals↗
PubMed1993

Experimental analysis of the control of expression of the homeobox-gene Msx-1 in the developing limb and face.

Mouse mesenchyme was grafted into chick embryos to investigate the control of mesenchymal expression of Msx-1 in the developing limb and face. In situ hybridization, using species-specific probes, allows a comparison between Msx-1 expression in the graft and the host tissue. The results show that Msx-1 expression in both limb-to-limb and face-to-face grafts corresponds closely with the level of Msx-1 expression in the surrounding chick mesenchyme. Cells in grafts that end up within the host domain of Msx-1 express the gene irrespective of whether they were from normally expressing, or non-expressing, regions. Therefore Msx-1 expression in both the developing limb and the developing face appears to be position-dependent. Mesenchyme from each of the three major facial primordia behaved in the same way when grafted to the chick maxillary primordium. Reciprocal grafts between face and limb gave a different result: Msx-1 expression was activated when facial mesenchyme was grafted to the limb but not when limb mesenchyme was grafted to the face. This suggests either that there are quantitative or qualitative differences in two local signalling systems or that additional factors determine the responsiveness of the mesenchyme cells.

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