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A genetic link between Tbx1 and fibroblast growth factor signaling

Francesca Vitelli1, Ilaria Taddei1, Masae Morishima1, Erik N. Meyers2, Elizabeth A. Lindsay1 and Antonio Baldini1,3,*

1 Department of Pediatrics (Cardiology), Baylor College of Medicine, Houston TX 77030, USA
2 Department of Pediatrics and Cell Biology, Duke University Medical Center, Durham NC 27710, USA
3 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston TX 77030, USA



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  		Fig. 1. Tbx1 and Fgf8 expression overlaps in the pharyngeal pouches at E10.5. Sagittal sections of an X-gal stained Tbx1 heterozygous embryo (A) compared with RNA in situ hybridization with Fgf8 of a wild-type embryo (B) showing a similar expression pattern, particularly in the fourth pharyngeal pouch (4). 3, third pharyngeal pouch; DAo, dorsal aorta; I, first pharyngeal arch; H, heart. Whole-mount in situ hybridization reveals loss of Fgf8 expression in the pharyngeal endoderm in Tbx1–/– (D) when compared with Tbx1+/– (C) mutants at E10.5. White arrowheads indicate the expression domain on the ectoderm covering the first arch, which is maintained in both embryos, and is also visible in B. o, otocyst. (E-H) Sagittal sections of an Fgf8 in situ hybridization of E10 wild-type (E), Tbx1+/– (F) and Tbx1–/– (G and H, lateral and medial sections, respectively, from the same embryo) embryos. Note the loss of expression in the pharyngeal endoderm of Tbx1–/– when compared with E,F, which are essentially identical. For all panels, anterior is upwards and dorsal is leftwards. Scale bars: 100 µm in A-B,E-H; 0.5 mm in C,D.

 


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  		Fig. 2. Both Tbx1 and Fgf10 are expressed in the paraxial mesodermal core of the cranial pharyngeal arches (A-D). Sagittal sections of an X-gal stained Tbx1 heterozygous mutant at E10.5 (A,C) compared with RNA in situ hybridization with Fgf10 on a wild-type embryo at E10.25 (B,D). In A and B, the Tbx1-positive and Fgf10-positive paraxial mesoderm (arrows) is seen as a stream of cells entering the first arch mesenchyme (I); o, otocyst. The more medial sections in C,D show the overlap of Tbx1 and Fgf10 expression in the mesodermal core of the second arch (II) as well (arrows). The arrowhead in D indicates Fgf10-positive cells in the ectoderm overlaying the first arch. Fgf10 expression in the paraxial mesoderm is absent in Tbx1 homozygous mutants at E10.25 (E, left side; F, right side of the same embryo), but is maintained in the first arch ectoderm (arrowhead in E). Some diffuse Fgf10 expression is detected in the mesenchyme of the first arch, but not in the hypoplastic second arch ("II"). For all panels, anterior is upwards and dorsal is leftwards. Scale bars: 100 µm.

 


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  		Fig. 3. Tbx1 and Fgf10 expression is similar in the presumptive secondary heart field. (A) An X-gal stained Tbx1+/– embryo at E10.5 showing positive cells in the dorsal wall of the pericardiac cavity, adjacent to and extending into the outflow tract (OFT; arrowheads in A, arows in B). DAo, dorsal aorta. B is an enlargement of the boxed area in A. (C) RNA in situ hybridization of Fgf10 on a wild-type E10.5 embryo; arrowhead indicates a cluster of cells thought to contribute to the OFT muscle wall. This cell population is missing in a stage-matched Tbx1 homozygous mutant (arrowhead in D indicates a comparable region of mesenchyme); I, first pharyngeal arch. Anterior is upwards and dorsal is leftwards in all panels. Scale bars: 100 µm.

 


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  		Fig. 4. Normal great vessel anatomy (A,C) compared with the most common defect observed in Tbx1+/–;Fgf8+/– animals (B,D) at E18.5 in dissected heart-lung preparations; anterior is upwards. The frontal view (A,B) reveals lack of a segment of the arch (indicated by an asterisk in A), a type B interruption. The dorsal view (C,D) shows a retro-esophageal connection between the ascending and descending aorta (desAo), probably cause by abnormal persistence of the right dorsal aorta; diluted iodine solution was injected into the aorta in D as a visual aid. Ao, aorta; PT, pulmonary trunk; rcc and lcc, right and left common carotid arteries; rsa and lsa, right and left subclavian arteries; t, trachea; e, esophagus. Scale bars: 1 mm.

 

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© The Company of Biologists Ltd 2002