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Ephrin-B1 forward and reverse signaling are required during mouse development.

Eph receptors and ephrin ligands are key players in many developmental processes including embryo patterning, angiogenesis, and axon guidance. Eph/ephrin interactions lead to the generation of a bidirectional signal, in which both the Eph receptors and the ephrins activate downstream signaling cascades simultaneously. To understand the role of ephrin-B1 and the importance of ephrin-B1-induced reverse signaling during embryonic development, we have generated mouse lines carrying mutations in the efnb1 gene. Complete ablation of ephrin-B1 resulted in perinatal lethality associated with a range of phenotypes, including defects in neural crest cell (NCC)-derived tissues, incomplete body wall closure, and abnormal skeletal patterning. Conditional deletion of ephrin-B1 demonstrated that ephrin-B1 acts autonomously in NCCs, and controls their migration. Last, a mutation in the PDZ binding domain indicated that ephrin-B1-induced reverse signaling is required in NCCs. Our results demonstrate that ephrin-B1 acts both as a ligand and as a receptor in a tissue-specific manner during embryogenesis.

Animals↗

The chicken talpid3 gene encodes a novel protein essential for Hedgehog signaling.

Talpid3 is a classical chicken mutant with abnormal limb patterning and malformations in other regions of the embryo known to depend on Hedgehog signaling. We combined the ease of manipulating chicken embryos with emerging knowledge of the chicken genome to reveal directly the basis of defective Hedgehog signal transduction in talpid3 embryos and to identify the talpid3 gene. We show in several regions of the embryo that the talpid3 phenotype is completely ligand independent and demonstrate for the first time that talpid3 is absolutely required for the function of both Gli repressor and activator in the intracellular Hedgehog pathway. We map the talpid3 locus to chromosome 5 and find a frameshift mutation in a KIAA0586 ortholog (ENSGALG00000012025), a gene not previously attributed with any known function. We show a direct causal link between KIAA0586 and the mutant phenotype by rescue experiments. KIAA0586 encodes a novel protein, apparently specific to vertebrates, that localizes to the cytoplasm. We show that Gli3 processing is abnormal in talpid3 mutant cells but that Gli3 can still translocate to the nucleus. These results suggest that the talpid3 protein operates in the cytoplasm to regulate the activity of both Gli repressor and activator proteins.

Amino Acid Sequence↗

A duplicated zone of polarizing activity in polydactylous mouse mutants.

The positional signaling along the anteroposterior axis of the developing vertebrate limb is provided by the zone of polarizing activity (ZPA) located at the posterior margin. Recently, it was established that the Sonic hedgehog (Shh) mediates ZPA activity. Here we report that a new mouse mutant, Recombination induced mutant 4 (Rim4), and two old mutants, Hemimelic extra toes (Hx) and Extra toes (Xt), exhibit mirror-image duplications of the skeletal pattern of the digits. In situ hybridization of the embryos of these mutants revealed ectopic expression of Shh and fibroblast growth factor-4 (Fgf-4) genes at the anterior margin of limb buds. The new mutation, Rim4, was mapped to chromosome 6 with linkage to HoxAbut segregated from HoxA. No linkage to other known polydactylous mutations was detected. In this mutant, ectopic expression of the Hoxd-11 gene, thought to be downstream of ZPA, was also observed at the anterior margin of the limb buds. All results indicate the presence of an additional ZPA at the anterior margin of limb buds in these mutants. Thus, it appears that multiple endogenous genes regulate the spatial localization of the ZPA in the developing mouse limb bud.

Animals↗

Triphalangeal thumb and brachyectrodactyly syndrome: an uncommon entity with evidence of geographic distribution.

A new Mexican family with the triphalangeal thumb-brachyectrodactyly syndrome is described. The proposita, a 17-year-old female, showed the classic malformation pattern: triphalangeal thumb, brachysyndactyly in the hands and ectrodactyly in the feet. Several members of the family had similar malformations, and others presented minor manifestations of the disease (brachydactyly and nail dysplasia). This is the fourth familial case reported in the literature with the triphalangeal thumb and brachyectrodactyly complex and the third of Mexican origin, reflecting a geographical predominance in the occurrence of this uncommon pathology.

Adolescent↗

Greig cephalopolysyndactyly syndrome: altered phenotype of a microdeletion syndrome due to the presence of a cytogenetic abnormality.

A male had several features of Greig cephalopolysyndactyly syndrome (GCPS) and significant developmental delay. He was found to have a de novo chromosomal deletion of chromosome no. 7 involving p13; this resulted in loss of the zinc finger gene, GLI3, which is the candidate gene in this syndrome. Modification of the CGPS phenotype in a sporadic case emphasizes the importance of searching for a chromosomal origin of this autosomal dominant disorder. Detection of a chromosomal deletion in these patients may be associated with a poor prognosis from the standpoint of cognitive development, and the potential for other structural abnormalities not normally associated with GCPS.

Abnormalities, Multiple↗

Sonic hedgehog expression in Gli3 depressed mouse embryo, Pdn/Pdn.

The phenotype of the genetic polydactyly/arhinencephaly mouse (Pdn/Pdn) is similar to Greig cephalopolysyndactyly syndrome (GCPS), which is induced by mutation of GLI3. Suppression of Gli3 gene expression has been observed in Pdn/Pdn. Thus, the gene responsible for Pdn/Pdn has been considered to be Gli3. Recently, the mutation point was demarcated, that is, a transposon was inserted into intron 3 of the Gli3 gene in the Pdn mouse. Forward and reverse primers were constructed in intron 3 near the insertion point. A forward primer in the long terminal repeat region of the transposon was also constructed. Now we can discriminate +/+, Pdn/+, Pdn/Pdn embryos from the PCR products. After genotyping of the Pdn embryos, Gli3 and other correlated gene expressions, such as sonic hedgehog (Shh), Bmp-2, Bmp-4, ptc-1, were analyzed by real-time PCR method. Gli3 gene expression in Pdn/Pdn was suppressed to 20-30% of +/+, and that in Pdn/+ was about 60% of +/+ through all the embryonic and neonatal periods examined. As Shh has been considered to be an antagonist of Gli3, Shh expression was analyzed, and a difference among genotypes was observed only on day 9 of gestation. We could not detect any alterations among genotypes in other gene expressions examined. Gli3 and Shh gene expression were also analyzed on day 9 by whole-mount in situ hybridization in the +/+ and Pdn/Pdn embryos. Neuroectoderm was positive by Gli3 probe in +/+ but not in Pdn/Pdn. Notochord, floor plate and prechordal mesoderm were positive by Shh probe both in +/+ and Pdn/Pdn embryos, but ectopic and/or over-expression of Shh were not observed in Pdn/Pdn embryos.

Animals↗

VACTERL association with a cleft hand.

Regarding radial ray deficiency, several reports suggest that preaxial limb anomalies occur frequently, while postaxial limb anomalies and cleft hand (split-hands) are rarely associated with VACTERL. We describe a rare clinical case of VACTERL with cleft hand and a number of visceral anomalies.

Abnormalities, Multiple↗

Exencephaly induction by valproic acid in the genetic polydactyly/arhinencephaly mouse, Pdn/Pdn.

Non-treated homozygous polydactyly/arhinencephaly (Pdn/Pdn) mouse fetuses exhibited exencephaly in 16.7% of cases. Treatment of Pdn/Pdn mice with 350 mg/kg of valproic acid (VPA) on days 8.5 and 9.5 of gestation increased the rate of exencephaly to 66.7%. The responsible gene for the Pdn mouse phenotype has been determined to be Gli3, and the suppression of Gli3 gene expression has been documented in Pdn/Pdn embryos. We investigated how the sonic hedgehog (Shh) and Fgf8 genes, the correlated genes of Gli3, are expressed in the VPA-treated exencephalic Pdn/Pdn embryos on day 10 of gestation, using whole mount in situ hybridization (WISH) and real-time PCR methods. We could not detect any alterations in Shh expression by real-time PCR, or WISH in the non-treated Pdn/Pdn and VPA-treated exencephalic Pdn/Pdn embryos. Altered Fgf8 expression patterns were observed in the commissural plate and dorsal isthmal neuroepithelium in the non-treated Pdn/Pdn embryos. We speculated that the altered expression of Fgf8 might be the result of down-regulation of Gli3 in Pdn/Pdn embryos. Fgf8 gene expression in the commissural plate and dorsal isthmal neuroepithelium exhibits wide or altered signal patterns in the VPA-treated exencephalic Pdn/Pdn embryo. From these findings, it was suggested that down-regulation of Gli3 gene expression induced the altered expression of Fgf8 in the Pdn/Pdn embryos, and that VPA treatment accelerated the alterations of Fgf8 gene expression in the Pdn/Pdn embryos. It was further speculated that altered expression of Fgf8 in the commissural plate may be the fundamental cause of exencephaly, and that the synergistic effect between gene and drug shown in this experiment may explain the differences of sensitivity in the side-effects of the drug.

Abnormalities, Multiple↗

Genetic susceptibility in the neural tube defects induced by ochratoxin A in the genetic arhinencephaly mouse, Pdn/Pdn.

It is well known that ochratoxin A (OTA) induces neural tube defects (NTDs) in mice. In the present study, OTA was administered to the genetic polydactyly/arhinencephaly mouse (Pdn/Pdn) to investigate the synergistic effect between gene and environmental toxin. OTA treatment on day 7.5 of gestation increased NTDs in the Pdn/Pdn mouse. The responsible gene for Pdn/Pdn is Gli3. So, it was speculated that specific susceptibility for OTA in the Pdn/Pdn mouse embryo may be due to the severe depression of Gli3 gene expression. As correlated genes, Gli3, Shh and Fgf8 gene expressions were examined in the Pdn mouse embryo on day 9 of gestation after administration of OTA on day 7.5. No alteration of Shh expression was observed in the non-treated Pdn/Pdn, and OTA-treated +/+ and Pdn/Pdn. Fgf8 signal was observed at the anterior neural ridge (ANR) in the non-treated +/+, and that was elongated in the non-treated Pdn/Pdn, and further elongated and more intensive in the OTA-treated Pdn/Pdn. It was suggested that Fgf8 gene expression was affected by the depression of Gli3, and alteration of Fgf8 gene expression was accelerated by the toxicity of OTA in the Pdn/Pdn.

Abnormalities, Multiple↗

Ectrodactyly in a West Highland white terrier.

A case of monomelic forelimb ectrodactyly (lobster-claw deformity) in a West Highland white terrier is reported. Clinical and radiographic findings are described. The dog was treated with a soft tissue reconstruction of the cleft. It later developed a slight varus-type deformity at the carpus but remained sound with occasional bouts of mild lameness following vigorous exercise. To the author's knowledge, this is the first reported case of canine ectrodactyly treated by simple cleft reconstruction, and only the second report of ectrodactyly in this breed.

Abnormalities, Multiple↗

BMP 7 is required for nephrogenesis, eye development, and skeletal patterning.

In summary, the generation of BMP-7-deficient mice has provided additional evidence that this family of growth factors regulate many morphogenetic processes including but not limited to skeletal development. In particular our experiments demonstrate that BMP 7 acts as an early inducer of glomeruli formation, and that it is required for skeletal patterning and lens formation. Our results not only demonstrate that BMP 7 is involved in the differentiation of several organs during development, but also raise the hypothesis that mutations in the Bmp 7 gene itself or in the genetic pathway could be responsible for several human genetic diseases in which glomerulus formation is impaired.

Animals↗

POLYDACTYLISM IN THE OFFSPRING OF MICE INJECTED WITH 5-BROMODEOXYURIDINE.

The intraperitoneal injection of multiple doses of 5-bromodeoxyuridine (BUDR) into pregnant mice produced abnormalities limited to the hind limbs of the offspring. This effect is probably a result of a metabolic lesion. When injected into newborn mice, BUDR did not increase the incidence of tumors.

Abnormalities, Drug-Induced↗

Altered growth and branching patterns in synpolydactyly caused by mutations in HOXD13.

Hox genes regulate patterning during limb development. It is believed that they function in the determination of the timing and extent of local growth rates. Here, it is demonstrated that synpolydactyly, an inherited human abnormality of the hands and feet, is caused by expansions of a polyalanine stretch in the amino-terminal region of HOXD13. The homozygous phenotype includes the transformation of metacarpal and metatarsal bones to short carpal- and tarsal-like bones. The mutations identify the polyalanine stretch outside of the DNA binding domain of HOXD13 as a region necessary for proper protein function.

Amino Acid Sequence↗

What you can learn from one gene: GLI3.

The study of patients with rare multiple congenital anomaly syndromes can provide illuminating insights into normal development and the pathogenesis of congenital anomalies. The GLI3 gene is a particularly good example as it illuminates the phenomena of pleiotropy, phenocopies, syndrome families, and evolutionary conservation of pathogenesis, and raises questions about how diagnoses are conceptualised. These topics are reviewed in turn, in the context of the clinical and biological data derived from patients with mutations in GLI3 and experimental work in model systems.

Abnormalities, Multiple↗