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PubMed2004

Dorso-ventral asymmetric functions of teashirt in Drosophila eye development depend on spatial cues provided by early DV patterning genes.

The teashirt (tsh) gene has dorso-ventral (DV) asymmetric functions in Drosophila eye development: promoting eye development in dorsal and suppressing eye development in ventral by Wingless mediated Homothorax (HTH) induction [Development 129 (2002) 4271]. We looked for DV spatial cues required by tsh for its asymmetric functions. The dorsal Iroquois-Complex (Iro-C) genes and Delta (Dl) are required and sufficient for the tsh dorsal functions. The ventral Serrate (Ser), but not fringe (fng) or Lobe (L), is required and sufficient for the tsh ventral function. We propose that DV asymmetric function of tsh represents a novel tier of DV pattern regulation, which takes place after the spatial expression patterns of early DV patterning genes are established in the eye.

Animals↗
PubMed2005

Homeotic selector genes control the patterning of seven-up expressing cells in the Drosophila dorsal vessel.

The linear cardiac tube of Drosophila, the dorsal vessel, is an important model organ for the study of cardiac specification and patterning in vertebrates. In Drosophila, the Hox segmentation gene abdominal-A (abd-A) is required for the specification of a functionally distinct heart region at the posterior of the dorsal vessel, from which blood is pumped anteriorly through a tube termed the aorta. Since we have previously shown that the posterior part of the aorta is specified during embryogenesis to form the adult heart during metamorphosis, we determined if the embryonic aorta is also patterned by the function of Hox segmentation genes. Using gain- and loss-of-function experiments, we demonstrate that the three Hox genes expressed in the posterior aorta and heart are sufficient to confer heart or posterior aorta fate throughout the dorsal vessel. Additionally, we demonstrate that Ultrabithorax and abd-A, but not Antennapedia, function to control cell number in the dorsal vessel. These studies add robustness to the model that homeotic selector genes pattern the Drosophila dorsal vessel, and further extend our understanding of how the cardiac tube is patterned in animal models.

Animals↗
PubMed2004

Role of fibroblast growth factor receptors 1 and 2 in the ureteric bud.

Fibroblast growth receptors (FGFRs) consist of four signaling family members. Mice with deletions of fgfr1 or fgfr2 are embryonic lethal prior to the onset of kidney development. To determine roles of FGFR1 and FGFR2 in the ureteric bud, we used a conditional targeting approach. First, we generated transgenic mice using the Hoxb7 promoter to drive cre recombinase and green fluorescent protein expression throughout ureteric bud tissue. We crossed Hoxb7creEGFP mice with mice carrying lox-p sites flanking critical regions of fgfr1 and/or fgfr2. Absence of fgfr1 from the ureteric bud (fgfr1(UB-/-)) results in no apparent renal abnormalities. In contrast, fgfr2(UB-/-) mice have very aberrant ureteric bud branching, thin ureteric bud stalks, and fewer ureteric bud tips. Fgfr2(UB-/-) ureteric bud tips also demonstrate inappropriate regions of apoptosis and reduced proliferation. The nephrogenic mesenchymal lineage in fgfr2(UB-/-) mice develops normal-appearing glomeruli and tubules, and only slightly fewer nephrons than controls. In contrast, fgfr2(UB-/-) kidneys have abnormally thickened subcapsular cortical stromal mesenchyme. Ultimately, fgfr2(UB-/-) adult kidneys are small and abnormally shaped or are hydronephrotic. Finally, there are no additional abnormalities in the fgfr1/2(UB-/-) kidneys versus the fgfr2(UB-/-) kidneys. In conclusion, FGFR2, but not FGFR1, appears crucial for ureteric bud branching morphogenesis and stromal mesenchyme patterning.

Animals↗
PubMed2006

BMP receptor type IA in limb bud mesenchyme regulates distal outgrowth and patterning.

The mesenchyme of the developing vertebrate limb responds to inductive signals, giving rise to skeletal elements that define limb shape and size. Several signals emanate from the limb ectoderm and in particular from the specialized epithelium of the apical ectodermal ridge (AER), including three members of the bone morphogenetic protein (BMP) family of signaling molecules, BMP2, BMP4 and BMP7. Using the Cre/loxP system in mice, we rendered limb bud mesenchyme insensitive to BMP signals through the type I receptor, BMPR-IA. Conditional mutants had shortened limbs and almost complete agenesis of the autopod because of reduced cell proliferation. Reduced expression of downstream BMP signaling targets, Msx1, Msx2 and gremlin in the distal mesenchyme (progress zone) correlated with decreased levels of cyclin D1 and Wnt5a. Ectopic anterior activation of sonic hedgehog (SHH) signaling and Hox expression revealed alterations in anterior-posterior (AP) patterning. Abnormal localization of Lmx1b-expressing cells in the ventral mesenchyme, along with histological alterations and an abnormal melanization pattern of the limb, indicate altered dorsal-ventral (DV) boundaries. These findings suggest that signaling through BMPR-IA in limb mesenchyme is essential for distal outgrowth and also influences AP and DV patterning.

Animals↗
PubMed2000

The expression of teneurin-4 in the avian embryo.

The teneurins are a family of four transmembrane proteins expressed in the developing vertebrate nervous system, though the Drosophila teneurin ten-m is also a pair-rule gene. Whole-mount in situ hybridization was used to localize teneurin-4 transcripts in the chicken embryo. The earliest signal is detected at stage 19 in the somites and limb buds. By stage 20 teneurin-4 transcripts are detected in temporal periocular mesenchyme, branchial arches, diencephalon and somites. Teneurin-4 expression in the limbs changes dramatically during development. Between stages 19 and 21 teneurin-4 expression is concentrated proximally in the zone of polarizing activity. Between stages 24 and 26 teneurin-4 is expressed in the mesenchyme of the anterodistal part of the limb. As in Drosophila, vertebrate teneurins are expressed not only in the nervous system, but also in non-neuronal tissues during pattern formation.

Amino Acid Sequence↗
PubMed1997

A role for Xenopus Gli-type zinc finger proteins in the early embryonic patterning of mesoderm and neuroectoderm.

Gli-type zinc finger proteins play important regulatory roles in vertebrate and invertebrate embryogenesis. In Xenopus, the Gli-type proteins XGli-3 and XGli-4 are first expressed in earliest stages of mesoderm and neural development. Transient transfection assays reveal that XGli-3 and XGli-4 can function as transcription repressors. Counteracting the Gli-protein repressor activity by ectopic expression of a fusion protein that contains the Gli-zinc finger cluster connected to the E1A activator domain in Xenopus embryos results in specific morphological alterations in the developing somites and in the central nervous system. Altered expression characteristics for a broad set of molecular markers highlighting specific aspects of mesodermal and neural differentiation demonstrate an important role for Gli-type zinc finger proteins in the early mesodermal and neural patterning of Xenopus embryos.

Amino Acid Sequence↗
PubMed2003

Regulation of axial patterning of the retina and its topographic mapping in the brain.

Topographic maps are a fundamental organizational feature of axonal connections in the brain. A prominent model for studying axial polarity and topographic map development is the vertebrate retina and its projection to the optic tectum (or superior colliculus). Linked processes are controlled by molecules that are graded along the axes of the retina and its target fields. Recent studies indicate that ephrin-As control the temporal-nasal mapping of the retina in the optic tectum/superior colliculus by regulating the topographically-specific interstitial branching of retinal axons along the anterior-posterior tectal axis. This branching is mediated by relative levels of EphA receptor repellent signaling. A major recent advance is the demonstration that EphB receptor forward signaling and ephrin-B reverse signaling mediate axon attraction to control dorsal-ventral retinal mapping along the lateral-medial tectal axis. In addition, several classes of regulatory proteins have been implicated in the control of the axial patterning of the retina, and its ultimate readout of topographic mapping.

Animals↗
PubMed2001

Distinct mechanisms regulate slow-muscle development.

Vertebrate muscle development begins with the patterning of the paraxial mesoderm by inductive signals from midline tissues [1, 2]. Subsequent myotome growth occurs by the addition of new muscle fibers. We show that in zebrafish new slow-muscle fibers are first added at the end of the segmentation period in growth zones near the dorsal and ventral extremes of the myotome, and this muscle growth continues into larval life. In marine teleosts, this mechanism of growth has been termed stratified hyperplasia [3]. We have tested whether these added fibers require an embryonic architecture of muscle fibers to support their development and whether their fate is regulated by the same mechanisms that regulate embryonic muscle fates. Although Hedgehog signaling is required for the specification of adaxial-derived slow-muscle fibers in the embryo [4, 5], we show that in the absence of Hh signaling, stratified hyperplastic growth of slow muscle occurs at the correct time and place, despite the complete absence of embryonic slow-muscle fibers to serve as a scaffold for addition of these new slow-muscle fibers. We conclude that slow-muscle-stratified hyperplasia begins after the segmentation period during embryonic development and continues during the larval period. Furthermore, the mechanisms specifying the identity of these new slow-muscle fibers are different from those specifying the identity of adaxial-derived embryonic slow-muscle fibers. We propose that the independence of early, embryonic patterning mechanisms from later patterning mechanisms may be necessary for growth.

Animals↗
PubMed2003

The Drosophila embryonic patterning determinant torsolike is a component of the eggshell.

The development of the head and tail regions of the Drosophila embryo is dependent upon the localized polar activation of Torso (Tor), a receptor tyrosine kinase that is uniformly distributed in the membrane of the developing embryo. Trunk (Trk), the proposed ligand for Tor, is secreted as an inactive precursor into the perivitelline fluid that lies between the embryonic membrane and the vitelline membrane (VM), the inner layer of the eggshell. The spatial regulation of Trk processing is thought to be mediated by the secreted product of the torsolike (tsl) gene, which is expressed during oogenesis by a specialized population of follicle cells present at the two ends of the oocyte. We show here that Tsl protein is specifically localized to the polar regions of the VM in laid eggs. We further demonstrate that although Tsl can associate with nonpolar regions of the VM, the activity of polar-localized Tsl is enhanced, suggesting the existence of another spatially restricted factor acting in this pathway. The incorporation of Tsl into the VM provides a mechanism for the transfer of spatial information from the follicle cells to the developing embryo. To our knowledge, Tsl represents the first example of an embryonic patterning determinant that is a component of the eggshell.

Animals↗
PubMed2000

Conservation and elaboration of Hox gene regulation during evolution of the vertebrate head.

The comparison of Hox genes between vertebrates and their closest invertebrate relatives (amphioxus and ascidia) highlights two derived features of Hox genes in vertebrates: duplication of the Hox gene cluster, and an elaboration of Hox expression patterns and roles compared with non-vertebrate chordates. We have investigated how new expression domains and their associated developmental functions evolved, by testing the cis-regulatory activity of genomic DNA fragments from the cephalochordate amphioxus Hox cluster in transgenic mouse and chick embryos. Here we present evidence for the conservation of cis-regulatory mechanisms controlling gene expression in the neural tube for half a billion years of evolution, including a dependence on retinoic acid signalling. We also identify amphioxus Hox gene regulatory elements that drive spatially localized expression in vertebrate neural crest cells, in derivatives of neurogenic placodes and in branchial arches, despite the fact that cephalochordates lack both neural crest and neurogenic placodes. This implies an elaboration of cis-regulatory elements in the Hox gene cluster of vertebrate ancestors during the evolution of craniofacial patterning.

Animals↗
PubMed2003

Gli proteins and the control of spinal-cord patterning.

The secreted protein sonic hedgehog (Shh) is crucial for the specification of neuronal subtype identity in the vertebrate neural tube. Zinc-finger proteins of the Gli family are known to be transcriptional mediators of Shh signalling, and to coordinately pattern the dorsal-ventral axis of the spinal cord. Recent studies indicate that additional signals may provide positional information in parallel to Shh to specify neuronal fate in this tissue. We review the role of Gli proteins in spinal-cord development and propose that various upstream patterning signals may be integrated by the Gli proteins to direct a coherent programme of neurogenesis.

Animals↗
PubMed1996

Body size and subcutaneous fat patterning in adolescence.

Factors that influence low birth weight at term may also be associated with subcutaneous fat patterning in later life. This hypothesis was investigated in a comparative (retrospective) cohort study. The subjects, born in Cardiff between 1975 and 1977, were of mean age 15.7 years. Cases (low birth weight (< 2500 g) at term) were matched with controls (normal birth weight (3000-3800 g) at term) for sex, parity, place of birth, date of birth, and gestation. Subscapular skinfold (an index of central subcutaneous fat) and triceps skinfold (an index of peripheral subcutaneous fat) were measured using a Holtain skinfold caliper. The differences (cases minus controls) (95% confidence interval) for subscapular and triceps skinfolds were respectively -0.3 mm (-1.74 to 1.14) and -0.48 mm (-1.75 to 0.79). These findings are inconsistent with the hypothesis that low birth weight at term is associated with subcutaneous fat patterning in adolescence.

Adipose Tissue↗
PubMed2004

Dorsal-ventral patterning and neural induction in Xenopus embryos.

We review the current status of research in dorsal-ventral (D-V) patterning in vertebrates. Emphasis is placed on recent work on Xenopus, which provides a paradigm for vertebrate development based on a rich heritage of experimental embryology. D-V patterning starts much earlier than previously thought, under the influence of a dorsal nuclear -Catenin signal. At mid-blastula two signaling centers are present on the dorsal side: The prospective neuroectoderm expresses bone morphogenetic protein (BMP) antagonists, and the future dorsal endoderm secretes Nodal-related mesoderm-inducing factors. When dorsal mesoderm is formed at gastrula, a cocktail of growth factor antagonists is secreted by the Spemann organizer and further patterns the embryo. A ventral gastrula signaling center opposes the actions of the dorsal organizer, and another set of secreted antagonists is produced ventrally under the control of BMP4. The early dorsal -Catenin signal inhibits BMP expression at the transcriptional level and promotes expression of secreted BMP antagonists in the prospective central nervous system (CNS). In the absence of mesoderm, expression of Chordin and Noggin in ectoderm is required for anterior CNS formation. FGF (fibroblast growth factor) and IGF (insulin-like growth factor) signals are also potent neural inducers. Neural induction by anti-BMPs such as Chordin requires mitogen-activated protein kinase (MAPK) activation mediated by FGF and IGF. These multiple signals can be integrated at the level of Smad1. Phosphorylation by BMP receptor stimulates Smad1 transcriptional activity, whereas phosphorylation by MAPK has the opposite effect. Neural tissue is formed only at very low levels of activity of BMP-transducing Smads, which require the combination of both low BMP levels and high MAPK signals. Many of the molecular players that regulate D-V patterning via regulation of BMP signaling have been conserved between Drosophila and the vertebrates.

Animals↗
PubMed2001

Early anterior/posterior patterning of the midbrain and cerebellum.

Transplantation studies performed in chicken embryos indicated that early anterior/posterior patterning of the vertebrate midbrain and cerebellum might be regulated by an organizing center at the junction between the midbrain and hindbrain. More than a decade of molecular and genetic studies have shown that such an organizer is indeed central to development of the midbrain and anterior hindbrain. Furthermore, a complicated molecular network that includes multiple positive and negative feedback loops underlies the establishment and refinement of a mid/hindbrain organizer, as well as the subsequent function of the organizer. In this review, we first introduce the expression patterns of the genes known to be involved in this patterning process and the quail-chick transplantation experiments that have provided the foundation for understanding the genetic pathways regulating mid/hindbrain patterning. Subsequently, we discuss the molecular genetic studies that have revealed the roles for many genes in normal early patterning of this region. Finally, some of the remaining questions and future directions are discussed.

Animals↗
PubMed2004

Expression of FoxE4 and Rx visualizes the timing and dynamics of critical processes taking place during initial stages of vertebrate eye development.

Several transcription factors have a critical function during initial stages of vertebrate eye formation. In this paper, we discuss the role of the Rx subfamily of homeobox-containing genes in retinal development, and the role of the Foxe3 and FoxE4 subfamily of forkhead box-containing genes in lens development. Rx genes are expressed in the initial stages of retinal development and they play a critical role in eye formation. Elimination of Rx function in mice results in lack of eye formation. Abnormal eye development observed in the mouse mutation eyeless (ey1), the medakatemperature-sensitive mutation eyeless (el), and the zebrafish mutation chokh are caused by abnormal regulation or function of Rx genes. In humans, a mutation in Rx leads to anophthalmia. In contrast, Foxe3 and FoxE4 genes are expressed in the lens and they play an essential role in its formation. Mutations in the Foxe3 gene are the cause of the mouse mutation dysgenetic lens (dyl) and in humans, mutation in FOXE3 leads to anterior segment dysgenesis and cataracts. Since Rx and FoxE4 are expressed in the earliest stages of retina and lens development, their expression visualizes the timing and dynamics of the crucial processes that comprise eye formation. In this paper we present a model of eye development based on the expression pattern of these two genes.

Animals↗
PubMed2003

Neural crest patterning: autoregulatory and crest-specific elements co-operate for Krox20 transcriptional control.

Neural crest patterning constitutes an important element in the control of the morphogenesis of craniofacial structures. Krox20, a transcription factor gene that plays a critical role in the development of the segmented hindbrain, is expressed in rhombomeres (r) 3 and 5 and in a stream of neural crest cells migrating from r5 toward the third branchial arch. We have investigated the basis of the specific neural crest expression of Krox20 and identified a cis-acting enhancer element (NCE) located 26 kb upstream of the gene that is conserved between mouse, man and chick and can recapitulate the Krox20 neural crest pattern in transgenic mice. Functional dissection of the enhancer revealed the presence of two conserved Krox20 binding sites mediating direct Krox20 autoregulation in the neural crest. In addition, the enhancer included another essential element containing conserved binding sites for high mobility group (HMG) box proteins and which responded to factors expressed throughout the neural crest. Consistent with this the NCE was strongly activated in vitro by Sox10, a crest-specific HMG box protein, in synergism with Krox20, and the inactivation of Sox10 prevented the maintenance of Krox20 expression in the migrating neural crest. These results suggest that the dependency of the enhancer on both crest- (Sox10) and r5- (Krox20) specific factors limits its activity to the r5-derived neural crest. This organisation also suggests a mechanism for the transfer and maintenance of rhombomere-specific gene expression from the hindbrain neuroepithelium to the emerging neural crest and may be of more general significance for neural crest patterning.

Animals↗
PubMed2004

The Cerberus/Dan-family protein Charon is a negative regulator of Nodal signaling during left-right patterning in zebrafish.

We have isolated a novel gene, charon, that encodes a member of the Cerberus/Dan family of secreted factors. In zebrafish, Fugu and flounder, charon is expressed in regions embracing Kupffer's vesicle, which is considered to be the teleost fish equivalent to the region of the mouse definitive node that is required for left-right (L/R) patterning. Misexpression of Charon elicited phenotypes similar to those of mutant embryos defective in Nodal signaling or embryos overexpressing Antivin(Atv)/Lefty1, an inhibitor for Nodal and Activin. Charon also suppressed the dorsalizing activity of all three of the known zebrafish Nodal-related proteins (Cyclops, Squint and Southpaw), indicating that Charon can antagonize Nodal signaling. Because Southpaw functions in the L/R patterning of lateral plate mesoderm and the diencephalon, we asked whether Charon is involved in regulating L/R asymmetry. Inhibition of Charon's function by antisense morpholino oligonucleotides (MOs) led to a loss of L/R polarity, as evidenced by bilateral expression of the left side-specific genes in the lateral plate mesoderm (southpaw, cyclops, atv/lefty1, lefty2 and pitx2) and diencephalon (cyclops, atv/lefty1 and pitx2), and defects in early (heart jogging) and late (heart looping) asymmetric heart development, but did not disturb the notochord development or the atv/lefty1-mediated midline barrier function. MO-mediated inhibition of both Charon and Southpaw led to a reduction in or loss of the expression of the left side-specific genes, suggesting that Southpaw is epistatic to Charon in left-side formation. These data indicate that antagonistic interactions between Charon and Nodal (Southpaw), which take place in regions adjacent to Kupffer's vesicle, play an important role in L/R patterning in zebrafish.

Amino Acid Sequence↗
PubMed2006

Requirements for Endothelin type-A receptors and Endothelin-1 signaling in the facial ectoderm for the patterning of skeletogenic neural crest cells in zebrafish.

Genetic studies in mice and zebrafish have revealed conserved requirements for Endothelin 1 (Edn1) signaling in craniofacial development. Edn1 acts through its cognate type-A receptor (Ednra) to promote ventral skeletal fates and lower-jaw formation. Here, we describe the isolation and characterization of two zebrafish ednra genes - ednra1 and ednra2 - both of which are expressed in skeletal progenitors in the embryonic neural crest. We show that they play partially redundant roles in lower-jaw formation and development of the jaw joint. Knockdown of Ednra1 leads to fusions between upper- and lower-jaw cartilages, whereas the combined loss of Ednra1 and Ednra2 eliminates the lower jaw, similar to edn1-/- mutants. edn1 is expressed in pharyngeal arch ectoderm, mesoderm and endoderm. Tissue-mosaic studies indicate that, among these tissues, a crucial source of Edn1 is the surface ectoderm. This ectoderm also expresses ednrA1 in an edn1-dependent manner, suggesting that edn1 autoregulates its own expression. Collectively, our results indicate that Edn1 from the pharyngeal ectoderm signals through Ednra proteins to direct early dorsoventral patterning of the skeletogenic neural crest.

Amino Acid Sequence↗