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Biomedical subjects

Rolf Zeller

Publications and source records attributed to Rolf Zeller.

17 recordsLinked to original sources
PubMed2006

Differential regulation of gene expression in the digit forming area of the mouse limb bud by SHH and gremlin 1/FGF-mediated epithelial-mesenchymal signalling.

Spatially and temporally coordinated changes in gene expression are crucial to orderly progression of embryogenesis. We combine mouse genetics with experimental manipulation of signalling to analyze the kinetics by which the SHH morphogen and the BMP antagonist gremlin 1 (GREM1) control gene expression in the digit-forming mesenchyme of mouse limb buds. Although most mesenchymal cells respond rapidly to SHH signalling, the transcriptional upregulation of specific SHH target signals in the mesenchyme occurs with differential temporal kinetics and in a spatially restricted fashion. In particular, the expression of the BMP antagonist Grem1 is always upregulated in mesenchymal cells located distal to the SHH source and acts upstream of FGF signalling by the apical ectodermal ridge. GREM1/FGF-mediated feedback signalling is, in turn, required to propagate SHH and establish the presumptive digit expression domains of the Notch ligand jagged 1 (Jag1) and 5'Hoxd genes in the distal limb bud mesenchyme. Their establishment is significantly delayed in Grem1-deficient limb buds and cannot be rescued by specific restoration of SHH signalling in mutant limb buds. This shows that GREM1/FGF feedback signalling is required for regulation of the temporal kinetics of the mesenchymal response to SHH signalling. Finally, inhibition of SHH signal transduction at distinct time points reveals the differential temporal dependence of Grem1, Jag1 and 5'Hoxd gene expression on SHH signalling. In particular, the expression of Hoxd13 depends on SHH signal transduction significantly longer than does Hoxd11 expression, revealing that the reverse co-linear establishment, but not maintenance of their presumptive digit expression domains, depends on SHH signalling.

Animals↗
PubMed2005

Genetic interaction of Gli3 and Alx4 during limb development.

The Gli3 and Alx4 transcriptional regulators are expressed in the anterior limb bud mesenchyme and their disruption in mice results in preaxial polydactyly. While the polydactylous phenotype of Alx4 deficient limb buds depends on SHH, the one of Gli3 deficient limb buds is completely independent of SHH signalling, suggesting that these genes act in parallel pathways. Analysis of limb buds lacking both Gli3 and Alx4 now shows that these two genes interact during limb skeletal morphogenesis. In addition to the defects in single mutants, the stylopod is severely malformed and the anterior element of the zeugopod is lost in double mutant limbs. However, limb bud patterning in Gli3-/-; Alx4-/- double mutant embryos is not affected more than in single mutants as the expression domains of key regulators remain the same. Most interestingly, the loss of the severe preaxial polydactyly characteristic of Gli3-/- limbs in double mutant embryos establishes that this type of polydactyly requires Alx4 function.

Animals↗
PubMed2004

It takes time to make a pinky: unexpected insights into how SHH patterns vertebrate digits.

It is widely accepted that the diffusible Sonic Hedgehog (SHH) morphogen signal establishes a spatial gradient that patterns embryonic structures by long-range signaling. In response, cell fates are determined by linear thresholds according to the position of cells within the gradient field. Two recent studies of SHH signaling during vertebrate limb development challenge this spatial gradient model. They establish that a large fraction of limb bud cells patterned by SHH are descendants of cells that have previously expressed Shh. These cells are endowed with a kinetic memory that integrates their exposure to SHH rather than sensing their position in a SHH gradient. In addition, a fraction of cells changes their SHH responsiveness progressively during limb bud pattering, which is indicative of local nonlinear modulation of cell fate specification.

Animals↗
PubMed2004

Gremlin-mediated BMP antagonism induces the epithelial-mesenchymal feedback signaling controlling metanephric kidney and limb organogenesis.

Epithelial-mesenchymal feedback signaling is the key to diverse organogenetic processes such as limb bud development and branching morphogenesis in kidney and lung rudiments. This study establishes that the BMP antagonist gremlin (Grem1) is essential to initiate these epithelial-mesenchymal signaling interactions during limb and metanephric kidney organogenesis. A Grem1 null mutation in the mouse generated by gene targeting causes neonatal lethality because of the lack of kidneys and lung septation defects. In early limb buds, mesenchymal Grem1 is required to establish a functional apical ectodermal ridge and the epithelial-mesenchymal feedback signaling that propagates the sonic hedgehog morphogen. Furthermore, Grem1-mediated BMP antagonism is essential to induce metanephric kidney development as initiation of ureter growth, branching and establishment of RET/GDNF feedback signaling are disrupted in Grem1-deficient embryos. As a consequence, the metanephric mesenchyme is eliminated by apoptosis, in the same way as the core mesenchymal cells of the limb bud.

Alleles↗
PubMed2004

Mouse limb deformity mutations disrupt a global control region within the large regulatory landscape required for Gremlin expression.

The mouse limb deformity (ld) mutations cause limb malformations by disrupting epithelial-mesenchymal signaling between the polarizing region and the apical ectodermal ridge. Formin was proposed as the relevant gene because three of the five ld alleles disrupt its C-terminal domain. In contrast, our studies establish that the two other ld alleles directly disrupt the neighboring Gremlin gene, corroborating the requirement of this BMP antagonist for limb morphogenesis. Further doubts concerning an involvement of Formin in the ld limb phenotype are cast, as a targeted mutation removing the C-terminal Formin domain by frame shift does not affect embryogenesis. In contrast, the deletion of the corresponding genomic region reproduces the ld limb phenotype and is allelic to mutations in Gremlin. We resolve these conflicting results by identifying a cis-regulatory region within the deletion that is required for Gremlin activation in the limb bud mesenchyme. This distant cis-regulatory region within Formin is also altered by three of the ld mutations. Therefore, the ld limb bud patterning defects are not caused by disruption of Formin, but by alteration of a global control region (GCR) required for Gremlin transcription. Our studies reveal the large genomic landscape harboring this GCR, which is required for tissue-specific coexpression of two structurally and functionally unrelated genes.

Amino Acid Sequence↗
PubMed2004

Liver regeneration in FGF-2-deficient mice: VEGF acts as potential functional substitute for FGF-2.

BACKGROUND/AIMS: The angiogenic properties, its role in mesoderm differentiation and cell culture studies implicate an important role of fibroblast growth factor (FGF-2) in liver regeneration. The aim of the study was to evaluate this role in a FGF-2 knockout mouse model. METHODS: Liver regeneration after left hemihepatectomy (partial hepatectomy, PH) was evaluated in homozygous FGF-2 deficient (-/-) mice (male C57BL/6J) and their FGF-2 competent (+/+) littermates (controls) (day 0-10). RESULTS: FGF-2-(-/-) mice displayed normal dynamics in liver regeneration. FGF-2 protein was overexpressed 4 days post PH in controls. BrdU incorporation showed a biphasic pattern in FGF-2-(-/-) mice, whereas it decreased continuously after one peak (day 2) in controls. In FGF-2-(-/-) livers hepatic growth factor mRNA post PH was 1 day longer decreased and markedly less elevated thereafter compared with control. Vascular endothelial growth factor (VEGF) mRNA levels were clearly increased in FGF-2-(-/-) mice pre- and postoperatively in contrast to controls. VEGF protein levels in livers of FGF-2-(-/-) mice were elevated preoperatively, but similar in both groups after PH. With SU5416, a VEGF-receptor inhibitor, liver regeneration in FGF-2-(-/-) mice was reduced significantly, whereas it remained unchanged in controls. CONCLUSIONS: Liver regeneration dynamics in FGF-2-(-/-) mice were comparable with controls, potentially due to a functional substitution of FGF-2 by VEGF.

Angiogenesis Inhibitors↗
PubMed2003

Glypican 4 modulates FGF signalling and regulates dorsoventral forebrain patterning in Xenopus embryos.

Heparan sulphate proteoglycans such as glypicans are essential modulators of intercellular communication during embryogenesis. In Xenopus laevis embryos, the temporal and spatial distribution of Glypican 4 (Gpc4) transcripts during gastrulation and neurulation suggests functions in early development of the central nervous system. We have functionally analysed the role of Xenopus Gpc4 by using antisense morpholino oligonucleotides and show that Gpc4 is part of the signalling network that patterns the forebrain. Depletion of GPC4 protein results in a pleiotropic phenotype affecting both primary axis formation and early patterning of the anterior central nervous system. Molecular analysis shows that posterior axis elongation during gastrulation is affected in GPC4-depleted embryos, whereas head and neural induction are apparently normal. During neurulation, loss of GPC4 disrupts expression of dorsal forebrain genes, such as Emx2, whereas genes marking the ventral forebrain and posterior central nervous system continue to be expressed. This loss of GPC4 activity also causes apoptosis of forebrain progenitors during neural tube closure. Biochemical studies establish that GPC4 binds FGF2 and modulates FGF signal transduction. Inhibition of FGF signal transduction, by adding the chemical SU5402 to embryos from neural plate stages onwards, phenocopies the loss of gene expression and apoptosis in the forebrain. We propose that GPC4 regulates dorsoventral forebrain patterning by positive modulation of FGF signalling.

Animals↗
PubMed2003

Synaptopodin-deficient mice lack a spine apparatus and show deficits in synaptic plasticity.

The spine apparatus is a cellular organelle that is present in many dendritic spines of excitatory neurons in the mammalian forebrain. Despite its discovery >40 years ago, the function of the spine apparatus is still unknown although calcium buffering functions as well as roles in synaptic plasticity have been proposed. We have recently shown that the 100-kDa protein synaptopodin is associated with the spine apparatus. Here, we now report that mice homozygous for a targeted deletion of the synaptopodin gene completely lack spine apparatuses. Interestingly, this absence of the spine apparatus is accompanied by a reduction in hippocampal long-term potentiation (LTP) in the CA1 region of the hippocampus and by an impairment of spatial learning in the radial arm maze test. This genetic analysis points to a role of the spine apparatus in synaptic plasticity.

Animals↗
PubMed2003

Patterning the limb before and after SHH signalling.

The vertebrate limb is one of the most relevant experimental models for analysing cell-cell signalling during patterning of embryonic fields and organogenesis. Recently, the combination of molecular and genetic studies with experimental manipulation of developing limb buds has significantly advanced our understanding of the complex molecular interactions co-ordinating limb bud outgrowth and patterning. Some of these studies have shown that there is a need to revise some of the textbook views of vertebrate limb development. In this review, we discuss how signalling by the polarizing region is established and how limb bud morphogenesis is controlled by both long-range and signal relay mechanisms. We also discuss recent results showing that differential mesenchymal responsiveness to SHH signalling is established prior to its expression by the polarizing region.

Animals↗
PubMed2003

Reduced mobility of fibroblast growth factor (FGF)-deficient myoblasts might contribute to dystrophic changes in the musculature of FGF2/FGF6/mdx triple-mutant mice.

Development and regeneration of muscle tissue is a highly organized, multistep process that requires cell proliferation, migration, differentiation, and maturation. Previous data implicate fibroblast growth factors (FGFs) as critical regulators of these processes, although their precise role in vivo is still not clear. We have explored the consequences of the loss of multiple FGFs (FGF2 and FGF6 in particular) for muscle regeneration in mdx mice, which serve as a model for chronic muscle damage. We show that the combined loss of FGF2 and FGF6 leads to severe dystrophic changes in the musculature. We found that FGF6 mutant myoblasts had decreased migration ability in vivo, whereas wild-type myoblasts migrated normally in a FGF6 mutant environment after transplantation of genetically labeled myoblasts from FGF6 mutants in wild-type mice and vice versa. In addition, retrovirus-mediated expression of dominant-negative versions of Ras and Ral led to a reduced migration of transplanted myoblasts in vivo. We propose that FGFs are critical components of the muscle regeneration machinery that enhance skeletal muscle regeneration, probably by stimulation of muscle stem cell migration.

Animals↗
PubMed2002

Progression of vertebrate limb development through SHH-mediated counteraction of GLI3.

Distal limb development and specification of digit identities in tetrapods are under the control of a mesenchymal organizer called the polarizing region. Sonic Hedgehog (SHH) is the morphogenetic signal produced by the polarizing region in the posterior limb bud. Ectopic anterior SHH signaling induces digit duplications and has been suspected as a major cause underlying congenital malformations that result in digit polydactyly. Here, we report that the polydactyly of Gli3-deficient mice arises independently of SHH signaling. Disruption of one or both Gli3 alleles in mouse embryos lacking Shh progressively restores limb distal development and digit formation. Our genetic analysis indicates that SHH signaling counteracts GLI3-mediated repression of key regulator genes, cell survival, and distal progression of limb bud development.

Animals↗
PubMed2002

Mutual genetic antagonism involving GLI3 and dHAND prepatterns the vertebrate limb bud mesenchyme prior to SHH signaling.

The bHLH transcription factor dHAND is required for establishment of SHH signaling by the limb bud organizer in posterior mesenchyme, a step crucial to development of vertebrate paired appendages. We show that the transcriptional repressor GLI3 restricts dHAND expression to posterior mesenchyme prior to activation of SHH signaling in mouse limb buds. dHAND, in turn, excludes anterior genes such as Gli3 and Alx4 from posterior mesenchyme. Furthermore, genetic interaction of GLI3 and dHAND directs establishment of the SHH/FGF signaling feedback loop by restricting the BMP antagonist GREMLIN posteriorly. These interactions polarize the nascent limb bud mesenchyme prior to SHH signaling.

Animals↗
PubMed2002

FGF2 signaling is required for the development of neuronal circuits regulating blood pressure.

Fibroblast growth factor 2 (FGF2) signaling is involved in angiogenesis, vascular contractility, and cardiac hypertrophy. Mice lacking a functional FGF2 gene (FGF2(-/-)) are hypotensive, but the primary physiological role of FGF2 in cardiovascular homeostasis remained unknown. Using a chicken FGF2 (cFGF2) transgene under control of the Wnt-1 promotor, we selectively re-expressed FGF2 in the developing nervous system of FGF2(-/-) (transgenic FGF2 mutant) embryos. Expression of the cFGF2 transgene in the developing nervous system, including its autonomic region, was limited to the period between embryonic day 9.5 and 14.5. Significantly, no FGF2 re-expression was detected in developing heart and blood vessels. Pharmacological analysis revealed a normalization of the blood pressure response to isoproterenol-induced vasodilation in adult transgenic FGF2 mutant mice. In addition, the hypotensive phenotype was rescued in 1 line (of 2) transgenic FGF2 mutant adult mice having expressed higher levels of cFGF2 proteins during nervous system development. These genetic studies indicate that FGF2 signaling is essential for complete development of the neural circuitry required for central regulation of blood pressure, whereas it appears dispensable for blood pressure control in the healthy adult. The full text of this article is available at http://www.circresaha.org.

Animals↗
PubMed2002

Mouse Twist is required for fibroblast growth factor-mediated epithelial-mesenchymal signalling and cell survival during limb morphogenesis.

Mouse Twist is essential for cranial neural tube, limb and somite development. [Genes Dev. 9 (1995) 686]. To identify the molecular defects disrupting limb morphogenesis, we have analysed expression of mesenchymal transcription factors involved in patterning and the cell-cell signalling cascades controlling limb bud development. These studies establish that Twist is essential for maintenance and progression of limb bud morphogenesis. In particular, the SHH/FGF signalling feedback loop operating between the polarizing region and the apical ectodermal ridge (AER) is disrupted. These defects in epithelial-mesenchymal signalling are most likely a direct consequence of disrupted fibroblast growth factor (FGF) signalling in Twist-deficient limb buds. In early limb buds, down-regulation of Fgf receptor 1 and Fgf10 expression in the mesenchyme occurs concurrent with loss of Fgf4 and Fgf8 expression in the AER. Finally, Twist function, most likely by regulating FGF signalling, is required for cell survival as apoptotic cells are detected in posterior and distal limb bud mesenchyme.

Animals↗
PubMed2002

1 Patterning the limb before and after SHH.

The Summer Meeting of the Anatomical Society of Great Britain and Ireland was held at the University of Dundee, from 23rd to 25th July 2002. It included a symposium on 'How to make a hand'. The following are abstracts of communications and posters presented at the meeting.

Journal Article↗
PubMed2000

Hepatocyte growth factor induces MAPK-dependent formin IV translocation in renal epithelial cells.

Renal epithelial tubule formation in cultured cells occurs after the addition of tubulogenic growth factors such as the hepatocyte growth factor (HGF). HGF activates the tyrosine kinase receptor c-met, initiating a series of complex events that regulate cell morphology, cell-cell interactions, and cell-matrix interactions and eventually result in the formation of branching tubular structures. The discovery that disruption of the formin gene locus in mice causes agenesis of the kidneys secondary to failure of ureteric bud outgrowth and branching tubule formation suggested that this family of proteins may be critical to the development of renal epithelial tubules. In this study, we investigated whether formin is involved in the HGF/c-met signaling pathway of in vitro tubulogenesis in renal epithelial cells. mIMCD-3 cells were analyzed by reverse transcription-PCR and found to express formin IV mRNA. With the use of an antibody that recognizes the carboxy terminus of all known formin isoforms, it was observed a formin isoform of approximately 165 kD markedly increased in the detergent soluble cell lysate after 10 min of stimulation with HGF. An antibody that is specific for formin IV was then generated and confirmed that the formin isoform regulated by HGF was formin IV. Cell fractionation and confocal localization of formin IV revealed that formin IV is primarily found in a submembranous band that co-localizes with the actin cytoskeleton and in a perinuclear location in quiescent epithelial cells but undergoes a rapid relocalization after HGF stimulation with translocation into the cell cytosol and into the nucleus. Formin IV was found to be a phosphorylation substrate for activated extracellular signal-regulated kinase in vitro, and pretreatment of cells with the mitogen-activated protein kinase inhibitor U0126 prevented the translocation of formin IV and inhibited HGF-dependent phosphorylation of formin IV in intact cells. In conclusion, activation of the c-met receptor results in cellular relocalization of formin IV in a mitogen-activated protein kinase-dependent manner.

Animals↗