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. 2012 Oct 5;91(4):629-35.
doi: 10.1016/j.ajhg.2012.08.014. Epub 2012 Sep 27.

Homeotic arm-to-leg transformation associated with genomic rearrangements at the PITX1 locus (VSports在线直播)

Malte Spielmann  1 , Francesco Brancati, Peter M Krawitz, Peter N Robinson, Daniel M Ibrahim, Martin Franke, Jochen Hecht, Silke Lohan, Katarina Dathe, Anna Maria Nardone, Paola Ferrari, Antonio Landi, Lars Wittler, Bernd Timmermann, Danny Chan, Ulrich Mennen, Eva Klopocki, Stefan Mundlos
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Homeotic arm-to-leg transformation associated with genomic rearrangements at the PITX1 locus

Malte Spielmann et al. Am J Hum Genet. .

Abstract

The study of homeotic-transformation mutants in model organisms such as Drosophila revolutionized the field of developmental biology, but how these mutants relate to human developmental defects remains to be elucidated. Here, we show that Liebenberg syndrome, an autosomal-dominant upper-limb malformation, shows features of a homeotic limb transformation in which the arms have acquired morphological characteristics of a leg. Using high-resolution array comparative genomic hybridization and paired-end whole-genome sequencing, we identified two deletions and a translocation 5' of PITX1. The structural changes are likely to remove active PITX1 forelimb suppressor and/or insulator elements and thereby move active enhancer elements in the vicinity of the PITX1 regulatory landscape VSports手机版. We generated transgenic mice in which PITX1 was misexpressed under the control of a nearby enhancer and were able to recapitulate the Liebenberg phenotype. .

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Figures

Figure 1
Figure 1
Pedigrees and Clinical Phenotypes of Three Unrelated Families Affected by Liebenberg Syndrome (A, B, and H) Pedigrees of Liebenberg-syndrome-affected families: family 1 (A), family 2 (B), and family 3 (H). Affected individuals are indicated by black symbols. Symbols with a “p” indicate individuals who were clinically examined and for whom further molecular analysis was performed. (C–G and J) Clinical presentation of affected individuals. Note radial deviation of hands and enlargement of wrists (E–G, I, and J). The elbows show flexion deformity causing the inability to fully straighten the joint and an appearance resembling anterior dislocation (C and D).
Figure 2
Figure 2
The Liebenberg Phenotype Is Characterized by a Partial Homeotic Arm-to-Leg Transformation Lateral X-ray of a normal elbow (A) and knee (E). Note the anatomical differences between the elbow (olecranon) and knee (patella) joints. In families 1 and 2, the olecranon is hypoplastic and the distal humerus is broadened at the elbow (B) and resembles the shape of a femur (E). The proximal head of the ulna is broadened (C) similarly to the tibial plateau of the knee joint. Three-dimensional computed tomography (CT) scans show a patella-like structure fused to the distal head of the humerus (G, outlined in white). The distal humerus has a medial and lateral condyle (F) separated by an intercondylar fossa (trench) resembling the femoral epicondyles of the knee. In family 3, the arm-to-leg-transformation phenotype is even more severe. The olecranon is completely missing (D), and the fusion of the triquetral and pisiform (D, outlined in yellow) forms an element that is similar not only in shape but also in size to the calcaneus in the ankle.
Figure 3
Figure 3
The Bones and Muscles of the Wrist Are Abnormal and Have Acquired Features Characteristic of the Ankle X-rays of the hands show elongated metacarpals resembling the metatarsals of the feet (A). In families 1 and 2, the apparent fusion of the triquetral and pisiform (A and D [outlined in yellow] and E [red arrow]) forms a structure similar in shape to the calcaneus of the ankle. These are separate bones in the normal wrist (C, yellow and blue). In addition, the scaphoid and lunate bones are fused (outlined in red in D and in red and green, respectively, in C) and form an element that is similar to the shape of the talus in the ankle. The arm-to-leg transformation additionally encompasses specific muscles and tendons. The extensor minimi digiti muscle straightens the little finger and is only present in the hand, but not in the foot. This muscle and its tendon are absent in the hands of Liebenberg individuals (B, indicated by yellow line). Similarly, the extensor carpi radialis muscle, a characteristic muscle of the hand, and its two tendons are absent in the Liebenberg individuals (B, indicated by red lines).
Figure 4
Figure 4
Genomic Rearrangements Appear to Result in a Misexpression of PITX1 in the Forelimb via the Activation of Ectopic Enhancers (A) Array CGH analysis in families 1 and 2 revealed overlapping heterozygous chromosome 5 deletions located 5′ of PITX1 and separated only by a gene desert. The Vista Enhancer Database indicates one highly conserved noncoding element hs1473 10 kb telomeric of the deleted region that shows forelimb- and hindlimb-specific enhancer activity (C) in E11.5 transgenic mouse embryos. (B) In family 3, paired-end whole-genome sequencing revealed a translocation, t(5;18)(q31.1;q12.3). Enhancer element hs1464, telomeric of the breakpoint, shows proximal forelimb-specific enhancer activity (C), and hs1440 shows forelimb- and hindlimb–specific enhancer activity (C).
Figure 5
Figure 5
E15.5 hs1473-Pitx1 Transgenic Embryos Showed Characteristic Features of a Forelimb-to-Hindlimb Transformation The mice showed loss of the olecranon (black arrow) and thus recapitulated the Liebenberg phenotype. Only one zeugopod bone was present. The distal head of the humerus was more similar to the distal femur, and the shape of the proximal head of the single zeugopodal element resembles the shape of the proximal tibia (red arrow). Two digits were missing, and the remaining digit I had two phalanges and was fused to the metacarpal of digit II. Fusions of the carpals formed a structure similar in shape to the calcaneus of the hindlimb (Figure 4, green arrows). Fusion of the carpals and radial deviation of the hands caused a foot-like appearance of the forelimb.
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