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Charles B Kimmel

Publications and source records attributed to Charles B Kimmel.

At least 19 recordsLinked to original sources
PubMed2006

Tbx16 cooperates with Wnt11 in assembling the zebrafish organizer.

The organizer, the signaling center that specifies vertebrate axial polarity and the nervous system, is a dorsal midline mesodermal domain in the gastrula that will form prechordal plate and anterior notochord. We show that in zebrafish the organizer is not a single domain when it first arises in the nascent mesoderm at the onset of gastrulation. Rather, in the presumptive prechordal plate region, the organizer is subdivided into two side-by-side cellular fields. Within minutes, concurrent medial and anterior cellular movements merge, or 'coalesce', the two fields to form the well-known singular midline field. Coalescence forms a symmetrical domain because the cell movements on the left and right sides initiate simultaneously and occur synchronously. However, in embryos with reduced function of the T-box transcription factor Tbx16 (Spadetail) or its genetic target paraxial protocadherin (Papc), synchrony is lost, coalesence is disrupted, and the midline domain is misshaped. Furthermore, with combined loss of Tbx16 and Wnt11 (Silberblick), coalesence is essentially absent. Possibly as a consequence, both the anterior movement of presumptive prechordal plate and organizer function, as assayed by eye-field separation, are disrupted. Our findings thus reveal that Tbx16, in combination with Wnt11, are critical components not only in morphogenesis but also in initial assembly of the organizer.

Animals↗
PubMed2006

Moz-dependent Hox expression controls segment-specific fate maps of skeletal precursors in the face.

Development of the facial skeleton depends on interactions between intrinsic factors in the skeletal precursors and extrinsic signals in the facial environment. Hox genes have been proposed to act cell-intrinsically in skeletogenic cranial neural crest cells (CNC) for skeletal pattern. However, Hox genes are also expressed in other facial tissues, such as the ectoderm and endoderm, suggesting that Hox genes could also regulate extrinsic signalling from non-CNC tissues. Here we study moz mutant zebrafish in which hoxa2b and hoxb2a expression is lost and the support skeleton of the second pharyngeal segment is transformed into a duplicate of the first-segment-derived jaw skeleton. By performing tissue mosaic experiments between moz(-) and wild-type embryos, we show that Moz and Hox genes function in CNC, but not in the ectoderm or endoderm, to specify the support skeleton. How then does Hox expression within CNC specify a support skeleton at the cellular level? Our fate map analysis of skeletal precursors reveals that Moz specifies a second-segment fate map in part by regulating the interaction of CNC with the first endodermal pouch (p1). Removal of p1, either by laser ablation or in the itga5(b926) mutant, reveals that p1 epithelium is required for development of the wild-type support but not the moz(-) duplicate jaw-like skeleton. We present a model in which Moz-dependent Hox expression in CNC shapes the normal support skeleton by instructing second-segment CNC to undergo skeletogenesis in response to local extrinsic signals.

Animals↗
PubMed2006

Zebrafish furin mutants reveal intricacies in regulating Endothelin1 signaling in craniofacial patterning.

Endothelin1 (Edn1) signaling promotes ventral character to the facial skeleton. In zebrafish edn1 mutants, the ventral jaw structures are severely reduced and fused to their dorsal counterparts, with a loss of joints that normally form at an intermediate dorsal-ventral position. Loss of function at another locus, sturgeon, also yields joint losses, but only mild reductions in the ventral jaw structures. We show that sturgeon encodes one of two orthologs of Furin present in zebrafish, and that both furin genes may function partially redundantly to activate Edn1 signaling. Supporting this hypothesis, early expression of edn1-dependent genes is downregulated in sturgeon (furinA) mutants. Later in development, expression of most of these genes recovers to near wild-type levels in furinA mutants but not in edn1 mutants. The recovery explains the less severe furinA mutant skeletal phenotype and suggests that late gene expression is dependent on a critical level of Edn1 signaling not present in the more severe edn1 mutants. However, expression defects in the intermediate joint-forming domains in both mutants persist, explaining the joint losses observed later in both mutants. We further show that in both mutants the arches fail to correctly undergo ventral elongation before skeletogenesis begins and propose a model in which this failure is largely responsible for the loss of an Edn1-dependent compartmentation of the arch into the intermediate and ventral domains.

Amino Acid Sequence↗
PubMed2006

Early Hedgehog signaling from neural to oral epithelium organizes anterior craniofacial development.

Hedgehog (Hh) signaling plays multiple roles in the development of the anterior craniofacial skeleton. We show that the earliest function of Hh is indirect, regulating development of the stomodeum, or oral ectoderm. A subset of post-migratory neural crest cells, that gives rise to the cartilages of the anterior neurocranium and the pterygoid process of the palatoquadrate in the upper jaw, condenses upon the upper or roof layer of the stomodeal ectoderm in the first pharyngeal arch. We observe that in mutants for the Hh co-receptor smoothened (smo) the condensation of this specific subset of crest cells fails, and expression of several genes is lost in the stomodeal ectoderm. Genetic mosaic analyses with smo mutants show that for the crest cells to condense the crucial target tissue receiving the Hh signal is the stomodeum, not the crest. Blocking signaling with cyclopamine reveals that the crucial stage, for both crest condensation and stomodeal marker expression, is at the end of gastrulation--some eight to ten hours before crest cells migrate to associate with the stomodeum. Two Hh genes, shh and twhh, are expressed in midline tissue at this stage, and we show using mosaics that for condensation and skeletogenesis only the ventral brain primordium, and not the prechordal plate, is an important Hh source. Thus, we propose that Hh signaling from the brain primordium is required for proper specification of the stomodeum and the stomodeum, in turn, promotes condensation of a subset of neural crest cells that will form the anterior neurocranial and upper jaw cartilage.

Animals↗
PubMed2005

Dynamic and sequential patterning of the zebrafish posterior hindbrain by retinoic acid.

A prominent region of the vertebrate hindbrain is subdivided along the anterior-posterior axis into a series of seven segments, or rhombomeres. The identity of each rhombomere is specified by the expression of conserved transcription factors, including Krox-20, vHnf1, Val (Kreisler, Mafb) and several Hox proteins. Previous work has shown that retinoic acid (RA) signaling plays a critical role in regulating the expression of these factors and that more posterior rhombomeres require higher levels of RA than more anterior rhombomeres. Models to account for RA concentration dependency have proposed either a static RA gradient or increasing time periods of RA exposure. Here, we provide evidence against both of these models. We show that early zebrafish rhombomere-specification genes, including vhnf1 in r5-r6 and hoxd4a in r7, initiate expression sequentially in the hindbrain, each adjacent to the source of RA synthesis in paraxial mesoderm. By knocking down RA signaling, we show that progressively more posterior rhombomeres require increasingly higher levels of RA signaling, and vhnf1 and hoxd4a expression are particularly RA-dependent. RA synthesis is required just at the time of initiation, but not for maintenance, of vhnf1 and hoxd4a expression. Furthermore, a premature RA increase causes premature activation of vhnf1 and hoxd4a expression. Our results support a new model of dynamic RA action in the hindbrain, in which a temporally increasing source of RA is required to sequentially initiate progressively more posterior rhombomere identities.

Animals↗
PubMed2005

Evolution and development of facial bone morphology in threespine sticklebacks.

How do developmental mechanisms evolve to control changing skeletal morphology, the shapes and sizes of individual bones? We address this question with studies of the opercle (OP), a large facial bone that has undergone marked morphological evolution in the ray-finned fish. Attributes for developmental analysis motivated us to examine how OP shape and size evolve and develop in threespine sticklebacks, a model system for understanding vertebrate evolution. We find that when Alaskan anadromous fish take up permanent residence in lakes, they evolve smaller and reshaped OPs. The change is a reduction in the amount of bone laid down along one body axis, and it arises at or shortly after the onset of OP development. A quantitative trait locus is present on linkage group 19 that contributes in a major way to this phenotype.

Alaska↗
PubMed2004

An integrin-dependent role of pouch endoderm in hyoid cartilage development.

Pharyngeal endoderm is essential for and can reprogram development of the head skeleton. Here we investigate the roles of specific endodermal structures in regulating craniofacial development. We have isolated an integrinalpha5 mutant in zebrafish that has region-specific losses of facial cartilages derived from hyoid neural crest cells. In addition, the cranial muscles that normally attach to the affected cartilage region and their associated nerve are secondarily reduced in integrinalpha5- animals. Earlier in development, integrinalpha5 mutants also have specific defects in the formation of the first pouch, an outpocketing of the pharyngeal endoderm. By fate mapping, we show that the cartilage regions that are lost in integrinalpha5 mutants develop from neural crest cells directly adjacent to the first pouch in wild-type animals. Furthermore, we demonstrate that Integrinalpha5 functions in the endoderm to control pouch formation and cartilage development. Time-lapse recordings suggest that the first pouch promotes region-specific cartilage development by regulating the local compaction and survival of skeletogenic neural crest cells. Thus, our results reveal a hierarchy of tissue interactions, at the top of which is the first endodermal pouch, which locally coordinates the development of multiple tissues in a specific region of the vertebrate face. Lastly, we discuss the implications of a mosaic assembly of the facial skeleton for the evolution of ray-finned fish.

Animals↗
PubMed2004

Parallel genetic basis for repeated evolution of armor loss in Alaskan threespine stickleback populations.

Most adaptation is thought to occur through the fixation of numerous alleles at many different loci. Consequently, the independent evolution of similar phenotypes is predicted to occur through different genetic mechanisms. The genetic basis of adaptation is still largely unknown, however, and it is unclear whether adaptation to new environments utilizes ubiquitous small-effect polygenic variation or large-effect alleles at a small number of loci. To address this question, we examined the genetic basis of bony armor loss in three freshwater populations of Alaskan threespine stickleback, Gasterosteus aculeatus, that evolved from fully armored anadromous populations in the last 14,000 years. Crosses between complete-armor and low-armor populations revealed that a single Mendelian factor governed the formation of all but the most anterior lateral plates, and another independently segregating factor largely determined pelvic armor. Genetic mapping localized the Mendelian genes to different chromosomal regions, and crosses among these same three widely separated populations showed that both bony plates and pelvic armor failed to fully complement, implicating the same Mendelian armor reduction genes. Thus, rapid and repeated armor loss in Alaskan stickleback populations appears to be occurring through the fixation of large-effect variants in the same genes.

Animals↗
PubMed2004

moz regulates Hox expression and pharyngeal segmental identity in zebrafish.

In vertebrate embryos, streams of cranial neural crest (CNC) cells migrate to form segmental pharyngeal arches and differentiate into segment-specific parts of the facial skeleton. To identify genes involved in specifying segmental identity in the vertebrate head, we screened for mutations affecting cartilage patterning in the zebrafish larval pharynx. We present the positional cloning and initial phenotypic characterization of a homeotic locus discovered in this screen. We show that a zebrafish ortholog of the human oncogenic histone acetyltransferase MOZ (monocytic leukemia zinc finger) is required for specifying segmental identity in the second through fourth pharyngeal arches. In moz mutant zebrafish, the second pharyngeal arch is dramatically transformed into a mirror-image duplicated jaw. This phenotype resembles a similar but stronger transformation than that seen in hox2 morpholino oligo (hox2-MO) injected animals. In addition, mild anterior homeotic transformations are seen in the third and fourth pharyngeal arches of moz mutants. moz is required for maintenance of most hox1-4 expression domains and this requirement probably at least partially accounts for the moz mutant homeotic phenotypes. Homeosis and defective Hox gene expression in moz mutants is rescued by inhibiting histone deacetylase activity with Trichostatin A. Although we find early patterning of the moz mutant hindbrain to be normal, we find a late defect in facial motoneuron migration in moz mutants. Pharyngeal musculature is transformed late, but not early, in moz mutants. We detect relatively minor defects in arch epithelia of moz mutants. Vital labeling of arch development reveals no detectable changes in CNC generation in moz mutants, but later prechondrogenic condensations are mispositioned and misshapen. Mirror-image hox2-dependent gene expression changes in postmigratory CNC prefigure the homeotic phenotype in moz mutants. Early second arch ventral expression of goosecoid (gsc) in moz mutants and in animals injected with hox2-MOs shifts from lateral to medial, mirroring the first arch pattern. bapx1, which is normally expressed in first arch postmigratory CNC prefiguring the jaw joint, is ectopically expressed in second arch CNC of moz mutants and hox2-MO injected animals. Reduction of bapx1 function in wild types causes loss of the jaw joint. Reduction of bapx1 function in moz mutants causes loss of both first and second arch joints, providing functional genetic evidence that bapx1 contributes to the moz-deficient homeotic pattern. Together, our results reveal an essential embryonic role and a crucial histone acetyltransferase activity for Moz in regulating Hox expression and segmental identity, and provide two early targets, bapx1 and gsc, of moz and hox2 signaling in the second pharyngeal arch.

Acetyltransferases↗
PubMed2004

An essential role for Fgfs in endodermal pouch formation influences later craniofacial skeletal patterning.

Fibroblast growth factor (Fgf) proteins are important regulators of pharyngeal arch development. Analyses of Fgf8 function in chick and mouse and Fgf3 function in zebrafish have demonstrated a role for Fgfs in the differentiation and survival of postmigratory neural crest cells (NCC) that give rise to the pharyngeal skeleton. Here we describe, in zebrafish, an earlier, essential function for Fgf8 and Fgf3 in regulating the segmentation of the pharyngeal endoderm into pouches. Using time-lapse microscopy, we show that pharyngeal pouches form by the directed lateral migration of discrete clusters of endodermal cells. In animals doubly reduced for Fgf8 and Fgf3, the migration of pharyngeal endodermal cells is disorganized and pouches fail to form. Transplantation and pharmacological experiments show that Fgf8 and Fgf3 are required in the neural keel and cranial mesoderm during early somite stages to promote first pouch formation. In addition, we show that animals doubly reduced for Fgf8 and Fgf3 have severe reductions in hyoid cartilages and the more posterior branchial cartilages. By examining early pouch and later cartilage phenotypes in individual animals hypomorphic for Fgf function, we find that alterations in pouch structure correlate with later cartilage defects. We present a model in which Fgf signaling in the mesoderm and segmented hindbrain organizes the segmentation of the pharyngeal endoderm into pouches. Moreover, we argue that the Fgf-dependent morphogenesis of the pharyngeal endoderm into pouches is critical for the later patterning of pharyngeal cartilages.

Animals↗
PubMed2003

Shaping the zebrafish notochord.

Promptly after the notochord domain is specified in the vertebrate dorsal mesoderm, it undergoes dramatic morphogenesis. Beginning during gastrulation, convergence and extension movements change a squat cellular array into a narrow, elongated one that defines the primary axis of the embryo. Convergence and extension might be coupled by a highly organized cellular intermixing known as mediolateral intercalation behavior (MIB). To learn whether MIB drives early morphogenesis of the zebrafish notochord, we made 4D recordings and quantitatively analyzed both local cellular interactions and global changes in the shape of the dorsal mesodermal field. We show that MIB appears to mediate convergence and can account for extension throughout the dorsal mesoderm. Comparing the notochord and adjacent somitic mesoderm reveals that extension can be regulated separately from convergence. Moreover, mutational analysis shows that extension does not require convergence. Hence, a cellular machine separate from MIB that can drive dorsal mesodermal extension exists in the zebrafish gastrula. The likely redundant control of morphogenesis may provide for plasticity at this critical stage of early development.

Animals↗
PubMed2003

Endothelin 1-mediated regulation of pharyngeal bone development in zebrafish.

Endothelin 1 (Edn1), a secreted peptide expressed ventrally in the primordia of the zebrafish pharyngeal arches, is required for correct patterning of pharyngeal cartilage development. We have studied mutants and morpholino-injected larvae to examine the role of the Edn1 signal in patterning anterior pharyngeal arch bone development during the first week after fertilization. We observe a remarkable variety of phenotypic changes in dermal bones of the anterior arches after Edn1 reduction, including loss, size reduction and expansion, fusion and shape change. Notably, the changes that occur appear to relate to the level of residual Edn1. Mandibular arch dermal bone fusions occur with severe Edn1 loss. In the dorsal hyoid arch, the dermal opercle bone is usually absent when Edn1 is severely reduced and is usually enlarged when Edn1 is only mildly reduced, suggesting that the same signal can act both positively and negatively in controlling development of a single bone. Position also appears to influence the changes: a branchiostegal ray, a dermal hyoid bone normally ventral to the opercle, can be missing in the same arch where the opercle is enlarged. We propose that Edn1 acts as a morphogen; different levels pattern specific positions, shapes and sizes of bones along the dorso-ventral axis. Changes involving Edn1 may have occurred during actinopterygian evolution to produce the efficient gill-pumping opercular apparatus of teleosts.

Animals↗
PubMed2003

Two endothelin 1 effectors, hand2 and bapx1, pattern ventral pharyngeal cartilage and the jaw joint.

A conserved endothelin 1 signaling pathway patterns the jaw and other pharyngeal skeletal elements in mice, chicks and zebrafish. In zebrafish, endothelin 1 (edn1 or sucker) is required for formation of ventral cartilages and joints in the anterior pharyngeal arches of young larvae. Here we present genetic analyses in the zebrafish of two edn1 downstream targets, the bHLH transcription factor Hand2 and the homeobox transcription factor Bapx1, that mediate dorsoventral (DV) patterning in the anterior pharyngeal arches. First we show that edn1-expressing cells in the first (mandibular) and second (hyoid) pharyngeal arch primordia are located most ventrally and surrounded by hand2-expressing cells. Next we show that along the DV axis of the early first arch primordia, bapx1 is expressed in an intermediate domain, which later marks the jaw joint, and this expression requires edn1 function. bapx1 function is required for formation of the jaw joint, the joint-associated retroarticular process of Meckel's cartilage, and the retroarticular bone. Jaw joint expression of chd and gdf5 also requires bapx1 function. Similar to edn1, hand2 is required for ventral pharyngeal cartilage formation. However, the early ventral arch edn1-dependent expression of five genes (dlx3, EphA3, gsc, msxe and msxb) are all present in hand2 mutants. Further, msxe and msxb are upregulated in hand2 mutant ventral arches. Slightly later, an edn1-dependent ventral first arch expression domain of gsc is absent in hand2 mutants, providing a common downstream target of edn1 and hand2. In hand2 mutants, bapx1 expression is present at the joint region, and expanded ventrally. In addition, expression of eng2, normally restricted to first arch dorsal mesoderm, expands ventrally in hand2 and edn1 mutants. Thus, ventral pharyngeal specification involves repression of dorsal and intermediate (joint region) fates. Together our results reveal two critical edn1 effectors that pattern the vertebrate jaw: hand2 specifies ventral pharyngeal cartilage of the lower jaw and bapx1 specifies the jaw joint.

Animals↗
PubMed2003

Zebrafish fgf24 functions with fgf8 to promote posterior mesodermal development.

Fibroblast growth factor (Fgf) signaling plays an important role during development of posterior mesoderm in vertebrate embryos. Blocking Fgf signaling by expressing a dominant-negative Fgf receptor inhibits posterior mesoderm development. In mice, Fgf8 appears to be the principal ligand required for mesodermal development, as mouse Fgf8 mutants do not form mesoderm. In zebrafish, Fgf8 is encoded by the acerebellar locus, and, similar to its mouse otholog, is expressed in early mesodermal precursors during gastrulation. However, zebrafish fgf8 mutants have only mild defects in posterior mesodermal development, suggesting that it is not the only Fgf ligand involved in the development of this tissue. We report here the identification of an fgf8-related gene in zebrafish, fgf24, that is co-expressed with fgf8 in mesodermal precursors during gastrulation. Using morpholino-based gene inactivation, we have analyzed the function of fgf24 during development. We found that inhibiting fgf24 function alone has no affect on the formation of posterior mesoderm. Conversely, inhibiting fgf24 function in embryos mutant for fgf8 blocks the formation of most posterior mesoderm. Thus, fgf8 and fgf24 are together required to promote posterior mesodermal development. We provide both phenotypic and genetic evidence that these Fgf signaling components interact with no tail and spadetail, two zebrafish T-box transcription factors that are required for the development of all posterior mesoderm. Last, we show that fgf24 is expressed in early fin bud mesenchyme and that inhibiting fgf24 function results in viable fish that lack pectoral fins.

Amino Acid Sequence↗
PubMed2002

The zebrafish T-box genes no tail and spadetail are required for development of trunk and tail mesoderm and medial floor plate.

T-box genes encode transcriptional regulators that control many aspects of embryonic development. Here, we demonstrate that the mesodermally expressed zebrafish spadetail (spt)/VegT and no tail (ntl)/Brachyury T-box genes are semi-redundantly and cell-autonomously required for formation of all trunk and tail mesoderm. Despite the lack of posterior mesoderm in spt(-);ntl(-) embryos, dorsal-ventral neural tube patterning is relatively normal, with the notable exception that posterior medial floor plate is completely absent. This contrasts sharply with observations in single mutants, as mutations singly in ntl or spt enhance posterior medial floor plate development. We find that ntl function is required to repress medial floor plate and promote notochord fate in cells of the wild-type notochord domain and that spt and ntl together are required non cell-autonomously for medial floor plate formation, suggesting that an inducing signal present in wild-type mesoderm is lacking in spt(-);ntl(-) embryos.

Alleles↗
PubMed2002

Two linked hairy/Enhancer of split-related zebrafish genes, her1 and her7, function together to refine alternating somite boundaries.

The formation of somites, reiterated structures that will give rise to vertebrae and muscles, is thought to be dependent upon a molecular oscillator that may involve the Notch pathway. hairy/Enhancer of split related [E(spl)]-related (her or hes) genes, potential targets of Notch signaling, have been implicated as an output of the molecular oscillator. We have isolated a zebrafish deficiency, b567, that deletes two linked her genes, her1 and her7. Homozygous b567 mutants have defective somites along the entire embryonic axis. Injection of a combination of her1 and her7 (her1+7) morpholino modified antisense oligonucleotides (MOs) phenocopies the b567 mutant somitic phenotype, indicating that her1 and her7 are necessary for normal somite formation and that defective somitogenesis in b567 mutant embryos is due to deletion of her1 and her7. Analysis at the cellular level indicates that somites in her1+7-deficient embryos are enlarged in the anterior-posterior dimension. Weak somite boundaries are often found within these enlarged somites which are delineated by stronger, but imperfect, boundaries. In addition, the anterior-posterior polarity of these enlarged somites is disorganized. Analysis of her1 MO-injected embryos and her7 MO-injected embryos indicates that although these genes have partially redundant functions in most of the trunk region, her1 is necessary for proper formation of the anteriormost somites and her7 is necessary for proper formation of somites posterior to somite 11. By following somite development over time, we demonstrate that her genes are necessary for the formation of alternating strong somite boundaries. Thus, even though two potential downstream components of Notch signaling are lacking in her1+7-deficient embryos, somite boundaries form, but do so with a one and a half to two segment periodicity.

Animals↗
PubMed2002

FGF3 and FGF8 mediate a rhombomere 4 signaling activity in the zebrafish hindbrain.

The segmentation of the vertebrate hindbrain into rhombomeres is highly conserved, but how early hindbrain patterning is established is not well understood. We show that rhombomere 4 (r4) functions as an early-differentiating signaling center in the zebrafish hindbrain. Time-lapse analyses of zebrafish hindbrain development show that r4 forms first and hindbrain neuronal differentiation occurs first in r4. Two signaling molecules, FGF3 and FGF8, which are both expressed early in r4, are together required for the development of rhombomeres adjacent to r4, particularly r5 and r6. Transplantation of r4 cells can induce expression of r5/r6 markers, as can misexpression of either FGF3 or FGF8. Genetic mosaic analyses also support a role for FGF signaling acting from r4. Taken together, our findings demonstrate a crucial role for FGF-mediated inter-rhombomere signaling in promoting early hindbrain patterning and underscore the significance of organizing centers in patterning the vertebrate neural plate.

Animals↗