Tissue-specific roles of Tbx1 in the development of the outer, middle and inner ear, defective in 22q11DS patients

Jelena S. Arnold, Evan M. Braunstein, Takahiro Ohyama, Andrew K. Groves, Joe C. Adams, M. Christian Brown, Bernice E. Morrow

Research output: Contribution to journalArticle

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Abstract

Most 22q11.2 deletion syndrome (22q11DS) patients have middle and outer ear anomalies, whereas some have inner ear malformations. Tbx1, a gene hemizygously deleted in 22q11DS patients and required for ear development, is expressed in multiple tissues during embryogenesis. To determine the role of Tbx1 in the first pharyngeal pouch (PPI) in forming outer and middle ears, we tissue-specifically inactivated the gene using Foxg1-Cre. In the conditional mutants, PPI failed to outgrow, preventing the middle ear bone condensations from forming. Tbx1 was also inactivated in the otic vesicle (OV), resulting in the failure of inner ear sensory organ formation, and in duplication of the cochleovestibular ganglion (CVG). Consistent with the anatomical defects, the sensory genes, Otx1 and Bmp4 were downregulated, whereas the CVG genes, Fgf3 and NeuroD, were upregulated. To delineate Tbx1 cell-autonomous roles, a more selective ablation, exclusively in the OV, was performed using Pax2-Cre. In contrast to the Foxg1-Cre mutants, Pax2-Cre conditional mutant mice survived to adulthood and had normal outer and middle ears but had the same inner ear defects as the Tbx1 null mice, with the same gene expression changes. These results demonstrate that Tbx1 has non-cell autonomous roles in PPI in the formation of outer and middle ears and cell-autonomous roles in the OV. Periotic mesenchymal markers, Prx2 and Brn4 were normal in both conditional mutants, whereas they were diminished in Tbx1-/- embryos. Thus, Tbx1 in the surrounding mesenchyme in both sets of conditional mutants cannot suppress the defects in the OV that occur in the null mutants.

Original languageEnglish (US)
Pages (from-to)1629-1639
Number of pages11
JournalHuman Molecular Genetics
Volume15
Issue number10
DOIs
StatePublished - May 15 2006

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DiGeorge Syndrome
External Ear
Middle Ear
Inner Ear
Ear
Ganglia
Genes
Mesoderm
Embryonic Development
Down-Regulation
Embryonic Structures
Gene Expression
Bone and Bones

ASJC Scopus subject areas

  • Genetics

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Tissue-specific roles of Tbx1 in the development of the outer, middle and inner ear, defective in 22q11DS patients. / Arnold, Jelena S.; Braunstein, Evan M.; Ohyama, Takahiro; Groves, Andrew K.; Adams, Joe C.; Brown, M. Christian; Morrow, Bernice E.

In: Human Molecular Genetics, Vol. 15, No. 10, 15.05.2006, p. 1629-1639.

Research output: Contribution to journalArticle

Arnold, Jelena S. ; Braunstein, Evan M. ; Ohyama, Takahiro ; Groves, Andrew K. ; Adams, Joe C. ; Brown, M. Christian ; Morrow, Bernice E. / Tissue-specific roles of Tbx1 in the development of the outer, middle and inner ear, defective in 22q11DS patients. In: Human Molecular Genetics. 2006 ; Vol. 15, No. 10. pp. 1629-1639.
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abstract = "Most 22q11.2 deletion syndrome (22q11DS) patients have middle and outer ear anomalies, whereas some have inner ear malformations. Tbx1, a gene hemizygously deleted in 22q11DS patients and required for ear development, is expressed in multiple tissues during embryogenesis. To determine the role of Tbx1 in the first pharyngeal pouch (PPI) in forming outer and middle ears, we tissue-specifically inactivated the gene using Foxg1-Cre. In the conditional mutants, PPI failed to outgrow, preventing the middle ear bone condensations from forming. Tbx1 was also inactivated in the otic vesicle (OV), resulting in the failure of inner ear sensory organ formation, and in duplication of the cochleovestibular ganglion (CVG). Consistent with the anatomical defects, the sensory genes, Otx1 and Bmp4 were downregulated, whereas the CVG genes, Fgf3 and NeuroD, were upregulated. To delineate Tbx1 cell-autonomous roles, a more selective ablation, exclusively in the OV, was performed using Pax2-Cre. In contrast to the Foxg1-Cre mutants, Pax2-Cre conditional mutant mice survived to adulthood and had normal outer and middle ears but had the same inner ear defects as the Tbx1 null mice, with the same gene expression changes. These results demonstrate that Tbx1 has non-cell autonomous roles in PPI in the formation of outer and middle ears and cell-autonomous roles in the OV. Periotic mesenchymal markers, Prx2 and Brn4 were normal in both conditional mutants, whereas they were diminished in Tbx1-/- embryos. Thus, Tbx1 in the surrounding mesenchyme in both sets of conditional mutants cannot suppress the defects in the OV that occur in the null mutants.",
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AB - Most 22q11.2 deletion syndrome (22q11DS) patients have middle and outer ear anomalies, whereas some have inner ear malformations. Tbx1, a gene hemizygously deleted in 22q11DS patients and required for ear development, is expressed in multiple tissues during embryogenesis. To determine the role of Tbx1 in the first pharyngeal pouch (PPI) in forming outer and middle ears, we tissue-specifically inactivated the gene using Foxg1-Cre. In the conditional mutants, PPI failed to outgrow, preventing the middle ear bone condensations from forming. Tbx1 was also inactivated in the otic vesicle (OV), resulting in the failure of inner ear sensory organ formation, and in duplication of the cochleovestibular ganglion (CVG). Consistent with the anatomical defects, the sensory genes, Otx1 and Bmp4 were downregulated, whereas the CVG genes, Fgf3 and NeuroD, were upregulated. To delineate Tbx1 cell-autonomous roles, a more selective ablation, exclusively in the OV, was performed using Pax2-Cre. In contrast to the Foxg1-Cre mutants, Pax2-Cre conditional mutant mice survived to adulthood and had normal outer and middle ears but had the same inner ear defects as the Tbx1 null mice, with the same gene expression changes. These results demonstrate that Tbx1 has non-cell autonomous roles in PPI in the formation of outer and middle ears and cell-autonomous roles in the OV. Periotic mesenchymal markers, Prx2 and Brn4 were normal in both conditional mutants, whereas they were diminished in Tbx1-/- embryos. Thus, Tbx1 in the surrounding mesenchyme in both sets of conditional mutants cannot suppress the defects in the OV that occur in the null mutants.

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