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S Mundlos

Publications and source records attributed to S Mundlos.

At least 19 recordsLinked to original sources
PubMed2001

A recurrent RNA-splicing mutation in the SEDL gene causes X-linked spondyloepiphyseal dysplasia tarda.

Spondyloepiphyseal dysplasia tarda (SEDL) is a genetically heterogeneous disorder characterized by mild-to-moderate short stature and early-onset osteoarthritis. Both autosomal and X-linked forms have been described. Elsewhere, we have reported the identification of the gene for the X-linked recessive form, which maps to Xp22.2. We now report characterization of an exon-skipping mutation (IVS3+5G-->A at the intron 3 splice-donor site) in two unrelated families with SEDL. Using reverse transcriptase (RT)-PCR, we demonstrated that the mutation resulted in elimination of the first 31 codons of the open reading frame. The mutation was not detected in 120 control X chromosomes. Articular cartilage from an adult who had SEDL and carried this mutation contained chondrocytes with abundant Golgi complexes and dilated rough endoplasmic reticulum (ER). RT-PCR experiments using mouse/human cell hybrids revealed that the SEDL gene escapes X inactivation. Homologues of the SEDL gene include a transcribed retropseudogene on chromosome 19, as well as expressed genes in mouse, rat, Drosophila melanogaster Caenorhabditis elegans, and Saccharomyces cerevisiae. The latter homologue, p20, has a putative role in vesicular transport from ER to Golgi complex. These data suggest that SEDL mutations may perturb an intracellular pathway that is important for cartilage homeostasis.

Adult↗
PubMed2001

Defects of human skeletogenesis--models and mechanisms.

Heritable diseases of the skeleton are a highly complex group of genetic disorders. Skeletal morphogenesis involves, in principle, four distinct developmental processes: patterning, organogenesis, growth and homeostasis. Defects in patterning affect the number and shape of bones and will result in dysostosis. Organogenesis involves the formation of bone and cartilage as an organ. Defects in growth plate function lead to abnormal proliferation and/or differentiation of chondrocytes resulting in dwarfism and dysplasia. Bone mass, shape and strength are maintained in equilibrium throughout development and adulthood (homeostasis). Animal studies are providing good correlations between specific embryological events and gene function, and consequently a framework for understanding the fundamental pathways that build and pattern bone. Based on the remarkable conservation of basic developmental mechanisms between animal species, connections to human disorders are frequently possible. As examples for recent advances in our understanding of the processes that underlie skeletal pathology, the molecular basis of a patterning defect, synpolydactyly, and a defect of organogenesis, cleidocranial dysplasia, will be presented and discussed.

Animals↗
PubMed2001

Heterozygous mutations in ANKH, the human ortholog of the mouse progressive ankylosis gene, result in craniometaphyseal dysplasia.

Craniometaphyseal dysplasia (CMD) is a bone dysplasia characterized by overgrowth and sclerosis of the craniofacial bones and abnormal modeling of the metaphyses of the tubular bones. Hyperostosis and sclerosis of the skull may lead to cranial nerve compressions resulting in hearing loss and facial palsy. An autosomal dominant form of the disorder (MIM 123000) was linked to chromosome 5p15.2-p14.1 (ref. 3) within a region harboring the human homolog (ANKH) of the mouse progressive ankylosis (ank) gene. The ANK protein spans the outer cell membrane and shuttles inorganic pyrophosphate (PPi), a major inhibitor of physiologic and pathologic calcification, bone mineralization and bone resorption. Here we carry out mutation analysis of ANKH, revealing six different mutations in eight of nine families. The mutations predict single amino acid substitutions, deletions or insertions. Using a helix prediction program, we propose for the ANK molecule 12 membrane-spanning helices with an alternate inside/out orientation and a central channel permitting the passage of PPi. The mutations occur at highly conserved amino acid residues presumed to be located in the cytosolic portion of the protein. Our results link the PPi channel ANK with bone formation and remodeling.

Amino Acid Sequence↗
PubMed2001

Sonic hedgehog is a survival factor for hypaxial muscles during mouse development.

Sonic hedgehog (Shh) has been proposed to function as an inductive and trophic signal that controls development of epaxial musculature in vertebrate embryos. In contrast, development of hypaxial muscles was assumed to occur independently of Shh. We here show that formation of limb muscles was severely affected in two different mouse strains with inactivating mutations of the Shh gene. The limb muscle defect became apparent relatively late and initial stages of hypaxial muscle development were unaffected or only slightly delayed. Micromass cultures and cultures of tissue fragments derived from limbs under different conditions with or without the overlaying ectoderm indicated that Shh is required for the maintenance of the expression of myogenic regulatory factors (MRFs) and, consecutively, for the formation of differentiated limb muscle myotubes. We propose that Shh acts as a survival and proliferation factor for myogenic precursor cells during hypaxial muscle development. Detection of a reduced but significant level of Myf5 expression in the epaxial compartment of somites of Shh homozygous mutant embryos at E9.5 indicated that Shh might be dispensable for the initiation of myogenesis both in hypaxial and epaxial muscles. Our data suggest that Shh acts similarly in both somitic compartments as a survival and proliferation factor and not as a primary inducer of myogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Distinct mutations in the receptor tyrosine kinase gene ROR2 cause brachydactyly type B.

Brachydactyly type B (BDB) is an autosomal dominant skeletal disorder characterized by hypoplasia/aplasia of distal phalanges and nails. Recently, heterozygous mutations of the orphan receptor tyrosine kinase (TK) ROR2, located within a distinct segment directly after the TK domain, have been shown to be responsible for BDB. We report four novel mutations in ROR2 (two frameshifts, one splice mutation, and one nonsense mutation) in five families with BDB. The mutations predict truncation of the protein within two distinct regions immediately before and after the TK domain, resulting in a complete or partial loss of the intracellular portion of the protein. Patients affected with the distal mutations have a more severe phenotype than do those with the proximal mutation. Our analysis includes the first description of homozygous BDB in an individual with a 5-bp deletion proximal to the TK domain. His phenotype resembles an extreme form of brachydactyly, with extensive hypoplasia of the phalanges and metacarpals/metatarsals and absence of nails. In addition, he has vertebral anomalies, brachymelia of the arms, and a ventricular septal defect-features that are reminiscent of Robinow syndrome, which has also been shown to be caused by mutations in ROR2. The BDB phenotype, as well as the location and the nature of the BDB mutations, suggests a specific mutational effect that cannot be explained by simple haploinsufficiency and that is distinct from that in Robinow syndrome.

Amino Acid Sequence↗
PubMed2000

Mouse mutant "rib-vertebrae" (rv): a defect in somite polarity.

The recessive mouse mutant rib-vertebrae (rv) affects the morphogenesis of the axial skeleton. The phenotype is characterized by vertebral defects such as fusion of adjacent segments, hemivertebrae, or open neural arches and rib defects including fusions, forked ribs, and additional ribs. We have analyzed this mutant in detail and are able to show that defective somite patterning underlies the vertebral malformations. The rv mutation leads to an elongation of the presomitic mesoderm and a disruption of the anterior-posterior polarization of somites, as indicated by the abnormal expression of Pax1 and Mox1. Somites are irregular in size but the overall formation of somites appears unaffected. These changes are reminiscent of somite defects obtained in loss of function alleles of the Delta-Notch pathway. Expression of the Notch pathway components Delta-like-1 (Dll1) and lunatic fringe (Lfng) are altered in rv mutants. To investigate possible interactions of rv with components of the Notch pathway, we crossed rv into Dll1(lacZ). Double heterozygous (rv/+; Dll1(lacZ)/+) mice show vertebral defects and homozygous animals with one inactive Dll1 allele (rv/rv; Dll1(lacZ)/+) exhibit a dramatic increase in phenotypic severity, indicating that rv and Dll1 genetically interact. We have mapped rv to a region on chromosome 7 that is syntenic to human chromosomes 11p, 10q, and 11p. rv is phenotypically similar to human vertebral malformations syndromes and can serve as a model for these conditions.

Animals↗
PubMed1999

Polytopic anomalies with agenesis of the lower vertebral column.

We describe clinical, pathological and radiological findings in 15 cases of sporadic and familial lower spine agenesis with additional anomalies of the axial skeleton and internal organs and speculate about the cause and pathogenesis of this malformation complex. We show that all of these findings are defects of blastogenesis, originate in the primary developmental field and/or the progenitor fields, thus representing polytopic field defects. This concept appears applicable in our cases and makes such terms such as "caudal regression syndrome" or "axial mesodermal dysplasia spectrum" redundant.

Abnormalities, Multiple↗
PubMed1999

Regulation of chondrocyte differentiation by Cbfa1.

Cbfa1, a developmentally expressed transcription factor of the runt family, was recently shown to be essential for osteoblast differentiation. We have investigated the role of Cbfa1 in endochondral bone formation using Cbfa1-deficient mice. Histology and in situ hybridization with probes for indian hedgehog (Ihh), collagen type X and osteopontin performed at E13.5, E14.5 and E17.5 demonstrated a lack of hypertrophic chondrocytes in the anlagen of the humerus and the phalanges and a delayed onset of hypertrophy in radius/ulna in Cbfa1-/- mice. Detailed analysis of Cbfa1 expression using whole mount in situ hybridization and a lacZ reporter gene reveled strong expression not only in osteoblasts but also in pre-hypertrophic and hypertrophic chondrocytes. Our studies identify Cbfa1 as a major positive regulator of chondrocyte differentiation.

Animals↗
PubMed1999

Mutation analysis of core binding factor A1 in patients with cleidocranial dysplasia.

Cleidocranial dysplasia (CCD) is a dominantly inherited disorder characterized by patent fontanelles, wide cranial sutures, hypoplasia of clavicles, short stature, supernumerary teeth, and other skeletal anomalies. We recently demonstrated that mutations in the transcription factor CBFA1, on chromosome 6p21, are associated with CCD. We have now analyzed the CBFA1 gene in 42 unrelated patients with CCD. In 18 patients, mutations were detected in the coding region of the CBFA1 gene, including 8 frameshift, 2 nonsense, and 9 missense mutations, as well as 2 novel polymorphisms. A cluster of missense mutations at arginine 225 (R225) identifies this residue as crucial for CBFA1 function. In vitro green fluorescent protein fusion studies show that R225 mutations interfere with nuclear accumulation of CBFA1 protein. There is no phenotypic difference between patients with deletions or frameshifts and those with other intragenic mutations, suggesting that CCD is generally caused by haploinsufficiency. However, we were able to extend the CCD phenotypic spectrum. A missense mutation identified in one family with supernumerary teeth and a radiologically normal skeleton indicates that mutations in CBFA1 can be associated exclusively with a dental phenotype. In addition, one patient with severe CCD and a frameshift mutation in codon 402 had osteoporosis leading to recurrent bone fractures and scoliosis, providing first evidence that CBFA1 may help maintain adult bone, in addition to its function in bone development.

Bone and Bones↗
PubMed1999

Cleidocranial dysplasia: clinical and molecular genetics.

Cleidocranial dysplasia (CCD) (MIM 119600) is an autosomal dominant skeletal dysplasia characterised by abnormal clavicles, patent sutures and fontanelles, supernumerary teeth, short stature, and a variety of other skeletal changes. The disease gene has been mapped to chromosome 6p21 within a region containing CBFA1, a member of the runt family of transcription factors. Mutations in the CBFA1 gene that presumably lead to synthesis of an inactive gene product were identified in patients with CCD. The function of CBFA1 during skeletal development was further elucidated by the generation of mutated mice in which the Cbfa1 gene locus was targeted. Loss of one Cbfa1 allele (+/-) leads to a phenotype very similar to human CCD, featuring hypoplasia of the clavicles and patent fontanelles. Loss of both alleles (-/-) leads to a complete absence of bone owing to a lack of osteoblast differentiation. These studies show that haploinsufficiency of CBFA1 causes the CCD phenotype. CBFA1 controls differentiation of precursor cells into osteoblasts and is thus essential for membranous as well as endochondral bone formation.

Animals↗
PubMed1998

Characterization of a human homologue of the Saccharomyces cerevisiae transcription factor spt3 (SUPT3H).

Spt3 is a Saccharomyces cerevisiae transcription factor that is required in vivo for the transcription of a number of RNA polymerase II-transcribed genes. We report the cloning of the gene encoding the human homologue of Spt3, SUPT3H, and its initial functional analysis. The human and yeast Spt3 homologues share an overall identity of 30% that defines three conserved regions, suggesting possible functional domains. To determine whether SUPT3H is a true functional Spt3 homologue, we tested for complementation of an spt3Delta mutation in yeast. While expression of the full-length SUPT3H is unable to complement an spt3Delta mutation, expression of a human-yeast chimeric gene that contains 42% human sequences can partially complement an spt3Delta mutation. These data suggest that the transcriptional control carried out by Spt3 has been conserved from yeast to human.

Amino Acid Sequence↗
PubMed1998

Acromesomelic dysplasia Maroteaux type maps to human chromosome 9.

Acromesomelic dysplasias are skeletal disorders that disproportionately affect the middle and distal segments of the appendicular skeleton. We report genetic mapping studies in four families with acromesomelic dysplasia Maroteaux type (AMDM), an autosomal recessive osteochondrodysplasia. A peak LOD score of 5.1 at recombination fraction 0 was obtained with fully informative markers on human chromosome 9. In three of the four families, the affected offspring are products of consanguineous marriages; if it is assumed that these affected offspring are homozygous by descent for the region containing the AMDM locus, a 6.9-cM AMDM candidate interval can be defined by markers D9S1853 and D9S1874. The mapping of the AMDM locus to human chromosome 9 indicates that AMDM is genetically distinct from the two other mapped acromesomelic dysplasias, Hunter-Thompson type and Grebe type, which are caused by mutations in CDMP1 on human chromosome 20.

Bone and Bones↗
PubMed1997

Synpolydactyly phenotypes correlate with size of expansions in HOXD13 polyalanine tract.

Synpolydactyly (SPD) is a dominantly inherited congenital limb malformation. Typical cases have 3/4 finger and 4/5 toe syndactyly, with a duplicated digit in the syndactylous web, but incomplete penetrance and variable expressivity are common. The condition has recently been shown to be caused by expansions of an imperfect trinucleotide repeat sequence encoding a 15-residue polyalanine tract in HOXD13. We have studied 16 new and 4 previously published SPD families, with between 7 and 14 extra residues in the tract, to analyze the molecular basis for the observed variation in phenotype. Although there is no evidence of change in expansion size within families, even over six generations, there is a highly significant increase in the penetrance and severity of phenotype with increasing expansion size, affecting both hands (P = 0.012) and feet (P < 0. 00005). Affected individuals from a family with a 14-alanine expansion, the largest so far reported, all have a strikingly similar and unusually severe limb phenotype, involving the first digits and distal carpals. Affected males from this family also have hypospadias, not previously described in SPD, but consistent with HOXD13 expression in the developing genital tubercle. The remarkable correlation between phenotype and expansion size suggests that expansion of the tract leads to a specific gain of function in the mutant HOXD13 protein, and has interesting implications for the role of polyalanine tracts in the control of transcription.

Base Sequence↗
PubMed1997

Cbfa1, a candidate gene for cleidocranial dysplasia syndrome, is essential for osteoblast differentiation and bone development.

We have generated Cbfa1-deficient mice. Homozygous mutants die of respiratory failure shortly after birth. Analysis of their skeletons revealed an absence of osteoblasts and bone. Heterozygous mice showed specific skeletal abnormalities that are characteristic of the human heritable skeletal disorder, cleidocranial dysplasia (CCD). These defects are also observed in a mouse Ccd mutant for this disease. The Cbfa1 gene was shown to be deleted in the Ccd mutation. Analysis of embryonic Cbfa1 expression using a lacZ reporter gene revealed strong expression at sites of bone formation prior to the earliest stages of ossification. Thus, the Cbfa1 gene is essential for osteoblast differentiation and bone formation, and the Cbfa1 heterozygous mouse is a paradigm for a human skeletal disorder.

Animals↗
PubMed1997

Mutations involving the transcription factor CBFA1 cause cleidocranial dysplasia.

Cleidocranial dysplasia (CCD) is an autosomal-dominant condition characterized by hypoplasia/aplasia of clavicles, patent fontanelles, supernumerary teeth, short stature, and other changes in skeletal patterning and growth. In some families, the phenotype segregates with deletions resulting in heterozygous loss of CBFA1, a member of the runt family of transcription factors. In other families, insertion, deletion, and missense mutations lead to translational stop codons in the DNA binding domain or in the C-terminal transactivating region. In-frame expansion of a polyalanine stretch segregates in an affected family with brachydactyly and minor clinical findings of CCD. We conclude that CBFA1 mutations cause CCD and that heterozygous loss of function is sufficient to produce the disorder.

Alleles↗
PubMed1997

Mouse clavicular development: analysis of wild-type and cleidocranial dysplasia mutant mice.

Cleidocranial dysplasia (CCD) is an autosomal dominant disease characterized by hypoplasia or aplasia of clavicles, open fontanelles, and other skeletal anomalies. A mouse mutant, shown by clinical and radiographic analysis to be strikingly similar to the human disorder and designated Ccd, was used as a model for the human disorder. Since malformation of the clavicle is the hallmark of CCD, we studied clavicular development in wild-type and Ccd mice. Histology and in situ hybridization experiments were performed to compare the temporal and spatial expression of several genes in wild-type and Ccd mutant mouse embryos. Bone and cartilage specific markers--type I, II, and X collagens, Sox9, aggrecan, and osteopontin were used as probes. The analyses covered the development of the clavicle from the initial mesenchymal condensation at embryonic day 13 (E13) to the late mineralization stage at embryonic day 15.5. At day 13.5, cells in the center of the condensation differentiate into characteristic precursor cells that were not observed in other bone anlagen. In the medial part of the anlage these cells express markers of the early cartilage lineage (type II collagen and Sox9), whereas cells of the lateral part express markers of the osteoblast lineage (type I collagen). With further development the medial cells differentiate into chondrocytes and start to express chondrocyte-specific markers such as aggrecan. Cells of the lateral part differentiate into osteoblasts as indicated by the production of bone matrix and the expression of osteopontin. At day 14.5 a regular growth plate has developed between the two parts where type X collagen expression can be demonstrated in hypertrophic chondrocytes. The data indicate that the medial part of the clavicle develops by endochondral bone formation while the lateral part ossifies as a membranous bone. The clavicle of Ccd mice showed a smaller band of mesenchymal cell condensation than in wild-type mice. Cells of the condensation failed to express type I and type II collagen at E13.5. In the lateral part of the clavicle type I collagen expression was not detected until E14.5 and osteopontin expression only appeared at E15.5. At E15.5, a small ossification center appears in the lateral part which is, in contrast to the wild-type clavicular bone, solid and without primary spongiosa as well as bone marrow. In the medial portion, type II collagen expression and endochondral ossification never occurs in Ccd mice; this portion of the clavicle is therefore missing in Ccd.

Animals↗
PubMed1997

The role of sonic hedgehog in vertebrate development.

Members of the hedgehog family are important signalling molecules during embryonic development. One member, Sonic hedgehog, is expressed in embryonic structures such as the zone of polarizing activity in the posterior limb bud, the notochord, and the floor plate of the neural tube, where it plays a role in patterning of the embryo. Sonic hedgehog is synthesized as an inactive precursor which must be proteolytically cleaved and modified by the addition of a cholesterol moiety to become active as a signalling molecule. In this processing, the C-terminal region of Sonic hedgehog serves as both the endoprotease and a cholesterol transferase. The importance of cholesterol for Sonic hedgehog function may explain many of the profound developmental defects caused by perturbations of cholesterol metabolism. The receptor for Sonic hedgehog is Patched, a multi-pass transmembrane protein which forms a complex with Smoothened Mutations in Patched are associated with basal cell naevus syndrome, while mutations in Sonic hedgehog cause holoprosencephaly. Downstream targets of Sonic hedgehog signalling are transcription factors like Gli3, responsible for Greigs polycephalosyndactyly in humans and Hoxd13, responsible for polysyndactyly.

Animals↗