Biomedical subjects

Erich Roessler

Publications and source records attributed to Erich Roessler.

10 recordsLinked to original sources

PubMed2006

Functional analysis of mutations in TGIF associated with holoprosencephaly.

Holoprosencephaly (HPE) is the most common structural malformation of the forebrain and face in humans. Our current understanding of the pathogenesis of HPE attempts to integrate genetic susceptibility, evidenced by mutations in the known HPE genes, with the epigenetic influence of environmental factors. Mutations or deletions of the human TGIF gene have been associated with HPE in multiple population cohorts. Here we examine the functional effects of all previously reported mutations, and describe four additional variants. Of the eleven sequence variations in TGIF, all but four can be demonstrated to be functionally abnormal. In contrast, no potentially pathogenic sequence alterations were detected in the related gene TGIF2. These results provide further evidence of a role for TGIF in HPE and demonstrate the importance of functional analysis of putative disease-associated alleles.

Animals↗

PubMed2006

A functional screen for sonic hedgehog regulatory elements across a 1 Mb interval identifies long-range ventral forebrain enhancers.

The secreted protein sonic hedgehog (Shh) plays an integral role in forming the ventral midline of the vertebrate central nervous system (CNS). In the absence of Shh function, ventral midline development is perturbed resulting in holoprosencephaly (HPE), a structural malformation of the brain, as well as in neuronal patterning and path finding defects along the length of the anteroposterior neuraxis. Central to the understanding of ventral neural tube development is how Shh transcription is regulated in the CNS. To address this issue, we devised an enhancer trap assay to systematically screen 1 Mb of DNA surrounding the Shh locus for the ability to target reporter gene expression to sites of Shh transcription in transgenic mouse embryos. This analysis uncovered six enhancers distributed over 400 kb, the combined activity of which covered all sites of Shh expression in the mouse embryonic CNS from the ventral forebrain to the posterior extent of the spinal cord. To evaluate the relative contribution of these enhancers to the overall pattern of Shh expression, individual elements were deleted in the context of a transgenic Bac reporter assay. Redundant mechanisms were found to control Shh-like reporter activity in the ventral spinal cord, hindbrain and regions of the telencephalon, whereas unique elements regulated Shh-like expression in the ventral midbrain, the majority of the ventral diencephalon and parts of the telencephalon. Three ventral forebrain enhancers locate on the distal side of translocation breakpoints that occurred upstream of Shh in human cases of HPE, suggesting that displacement of these regulatory elements from the Shh promoter is a likely cause of HPE in these individuals.

Animals↗

PubMed2005

A previously unidentified amino-terminal domain regulates transcriptional activity of wild-type and disease-associated human GLI2.

Zinc finger-containing Gli proteins mediate responsiveness to Hedgehog (Hh) signaling, with Gli2 acting as the major transcriptional activator in this pathway in mice. The discovery of disease-associated mutations points to a critical role for GLI2 in human Hh signaling as well. Here, we show that human GLI2 contains previously undescribed 5' sequence, extending the amino-terminus an additional 328 amino acids. In vitro, transcriptional activity of full-length GLI2 is up to 30 times lower than that of GLI2DeltaN (previously thought to represent the entire GLI2 protein), revealing the presence of an amino-terminal repressor domain in the full-length protein. GLI2DeltaN also exhibits potent transcriptional activity in vivo: overexpression in mouse skin leads to the formation of Hh-independent epithelial downgrowths resembling basal cell carcinomas, which in humans are associated with constitutive Hh signaling. The discovery of this additional, functionally relevant GLI2 sequence led us to re-examine several pathogenic human GLI2 mutants, now containing the entire amino-terminal domain. On the basis of the functional domains affected by the mutations, mutant GLI2 proteins exhibited either loss-of-function or dominant-negative activity. Moreover, deletion of the amino-terminus abrogated dominant-negative activity of mutant GLI2, revealing that this domain is required for transcriptional repressor activity of pathogenic GLI2. Our results establish the presence of an amino-terminal transcriptional repressor domain that plays a critical role in modulating the function of wild-type GLI2 and is essential for dominant-negative activity of a GLI2 mutant associated with human disease.

Animals↗

PubMed2003

Loss-of-function mutations in the human GLI2 gene are associated with pituitary anomalies and holoprosencephaly-like features.

Diminished Sonic Hedgehog (Shh) signaling is associated with the most common forebrain defect in humans, holoprosencephaly (HPE), which includes cyclopia, a phenotype also seen in mice and other vertebrates with defective Shh signaling. The secreted protein Shh acts as a crucial factor that patterns the ventral forebrain and is required for the division of the primordial eye field and brain into two discrete halves. Gli2 is one of three vertebrate transcription factors implicated as obligatory mediators of Shh signal transduction. Here, we show that loss-of-function mutations in the human GLI2 gene are associated with a distinctive phenotype (within the HPE spectrum) whose primary features include defective anterior pituitary formation and pan-hypopituitarism, with or without overt forebrain cleavage abnormalities, and HPE-like midfacial hypoplasia. We also demonstrate that these mutations lack GLI2 activity. We report on a functional association between GLI2 and human disease and highlight the role of GLI2 in human head development.

Alleles↗

PubMed2003

SONIC HEDGEHOG mutations causing human holoprosencephaly impair neural patterning activity.

Holoprosencephaly (HPE) is a common forebrain malformation associated with mental retardation and craniofacial anomalies. Multiple lines of evidence indicate that loss of ventral neurons is associated with HPE. The condition is etiologically heterogeneous, and abnormalities in any of several genes can cause human HPE. Among these genes, mutations in SONIC HEDGEHOG ( SHH) are the most commonly identified single gene defect causing human HPE. SHH mediates a number of processes in central nervous system development and is required for the normal induction of ventral cell types in the brain and spinal cord. Although a number of missense mutations in SHH have been identified in patients with HPE, the functional significance of these mutations has not yet been determined. We demonstrate that two SHH mutations that cause human HPE result in decreased in vivo activity of SHH in the developing nervous system. These mutant forms of SHH fail to regulate genes properly that are normally responsive to SHH signaling and do not induce ventrally expressed genes. In addition, the immunoreactivity of the mutant proteins is altered, suggesting that the conformation of the SHH protein has been disrupted. These studies are the first demonstration that mutations in SHH associated with human HPE perturb the in vivo patterning function of SHH in the developing nervous system.

Amino Acid Sequence↗

PubMed2003

How a Hedgehog might see holoprosencephaly.

Detailed knowledge of the Hedgehog signaling pathway is fundamental to an understanding of vertebrate development as well as several birth defects in humans. Here we review various aspects of Hedgehog synthesis, secretion, distribution and function in the context of the most common anomaly of the developing forebrain in humans, holoprosencephaly. Genetic studies in numerous model organisms are beginning to elucidate the factors that are likely candidates for the causes of early embryonic defects in humans, including holoprosencephaly.

Animals↗

PubMed2003

Novel mutation in sonic hedgehog in non-syndromic colobomatous microphthalmia.

Ocular (uveoretinal) colobomas occur in one in 10,000 individuals and present a substantive cause of congenital poor vision. The genetic bases of most forms of uveoretinal coloboma are elusive; mutations in PAX2 are found in only a few cases of coloboma of the retina and optic nerve that occur with renal anomalies as part of the renal-coloboma syndrome (MIM#120330; #167409). From experimental data that upstream expression of sonic hedgehog (SHH) controls Pax2 expression in mice and zebrafish, and from clinical experience that colobomas are observed frequently in patients with holoprosencephaly, we hypothesized that SHH could be a candidate for non-syndromic ocular colobomas (NSOC). We identified a three-generation family in which both a proband and his mother presented with iris and uveoretinal colobomas without optic nerve involvement. A novel 24 bp deletion in the gene SHH was identified in these affected family members, and cosegregated with the phenotype. This is the first report of the association of SHH mutations and uveoretinal coloboma.

Adult↗

PubMed2002

A loss-of-function mutation in the CFC domain of TDGF1 is associated with human forebrain defects.

TDGF1 (CRIPTO) is an EGF-CFC family member and an obligate co-receptor involved in NODAL signaling, a developmental program implicated in midline, forebrain, and left-right axis development in model organisms. Previous studies of CFC1 (CRYPTIC), another member of the EGF-CFC family, demonstrated that normal function of this protein is required for proper laterality development in humans. Here we identify a mutation in the conserved CFC domain of TDGF1 in a patient with midline anomalies of the forebrain. The mutant protein is inactive in a zebrafish rescue assay, indicating a role for TDGF1 in human midline and forebrain development.

Amino Acid Motifs↗

PubMed2002

Mutations in PATCHED-1, the receptor for SONIC HEDGEHOG, are associated with holoprosencephaly.

Holoprosencephaly (HPE) is the most commonly occurring congenital structural forebrain anomaly in humans. HPE is associated with mental retardation and craniofacial malformations. The genetic causes of HPE have recently begun to be identified, and we have previously shown that HPE can be caused by haploinsufficiency for SONIC HEDGEHOG ( SHH). We hypothesize that mutations in genes encoding other components of the SHH signaling pathway could also be associated with HPE. PATCHED-1 (PTCH), the receptor for SHH, normally acts to repress SHH signaling. This repression is relieved when SHH binds to PTCH. We analyzed PTCH as a candidate gene for HPE. Four different mutations in PTCHwere detected in five unrelated affected individuals. We predict that by enhancing the repressive activity of PTCH on the SHH pathway, these mutations cause decreased SHH signaling, and HPE results. The mutations could affect the ability of PTCH to bind SHH or perturb the intracellular interactions of PTCH with other proteins involved in SHH signaling. These findings further demonstrate the genetic heterogeneity associated with HPE, as well as showing that mutations in different components of a single signaling pathway can result in the same clinical condition.

Child↗

PubMed2002

CFC1 mutations in patients with transposition of the great arteries and double-outlet right ventricle.

Recent investigations identified heterozygous CFC1 mutations in subjects with heterotaxy syndrome, all of whom had congenital cardiac malformations, including malposition of the great arteries. We hypothesized that a subset of patients with similar types of congenital heart disease---namely, transposition of the great arteries and double-outlet right ventricle, in the absence of laterality defects---would also have CFC1 mutations. Our analysis of the CFC1 gene in patients with these cardiac disorders identified two disease-related mutations in 86 patients. The present study identifies the first autosomal single-gene defect for these cardiac malformations and indicates that some cases of transposition of the great arteries and double-outlet right ventricle can share a common genetic etiology with heterotaxy syndrome. In addition, these results demonstrate that the molecular pathway involving CFC1 plays a critical role in normal and abnormal cardiovascular development.

Base Sequence↗