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Human Molecular Genetics Advance Access published online on October 17, 2006
Human Molecular Genetics, doi:10.1093/hmg/ddl416
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© The Author 2006. Published by Oxford University Press. All rights reserved
Received June 8, 2006
Revised October 12, 2006
Accepted October 12, 2006

Article

Cyp26 genes a1, b1 and c1 are down-regulated in Tbx1 null mice and inhibition of Cyp26 enzyme function produces a phenocopy of DiGeorge Syndrome in the chick

Catherine Roberts 1, Sarah Ivins 1, Andrew C. Cook 2, Antonio Baldini 3, and Peter J. Scambler 1 *

1 Molecular Medicine Unit, Institute of Child Health, 30 Guilford St, London WC1N 1EH, UK
2 Cardiac Unit, Institute of Child Health, 30 Guilford St, London WC1N 1EH, UK
3 Institute of Biosciences and Technology, Texas A&M University Health Sciences Center, 2121 W. Holcombe Blvd. Houston, TX 77030 USA

* To whom correspondence should be addressed.
Peter J. Scambler, E-mail: p.scambler{at}ich.ucl.ac.uk


  Abstract

Cyp26a1, a gene required for retinoic acid (RA) inactivation during embryogenesis, was previously identified as a potential Tbx1 target from a microarray screen comparing wild type and null Tbx1 mouse embryo pharyngeal arches at E9.5. Using real-time PCR (RTQ-PCR) and in situ hybridization analysis of Cyp26a1 and its two functionally related family members Cyp26b1 and c1, we demonstrate reduced and/or altered expression for all three genes in pharyngeal tissues of Tbx1 null embryos. Blockade of Cyp26 function in the chick embryo using R115866, a specific inhibitor of Cyp26 enzyme function, resulted in a dose-dependent phenocopy of the Tbx1 null mouse including loss of caudal pharyngeal arches (pa) and arch arteries (paa), small otic vesicles, loss of head mesenchyme and, at later stages, DGS-like heart defects, including common arterial trunk (CAT) and perimembranous ventricular septal defects (VSD). Molecular markers revealed a serious disruption of pharyngeal pouch endoderm (ppe) morphogenesis and reduced staining for smooth muscle cells in pharyngeal arch arteries. Expression of the RA synthesizing enzyme Raldh2 was also up-regulated and altered Hoxb1 expression indicated that RA levels are raised in R115866-treated embryos as reported for Tbx1 null mice. Down-regulation of Tbx1 itself was observed, in accordance with previous observations that RA represses Tbx1 expression. Thus, by specifically blocking the action of the Cyp26 enzymes we can recapitulate many elements of the Tbx1 mutant mouse, supporting the hypothesis that the dysregulation of RA controlled morphogenesis contributes to the Tbx1 loss of function phenotype.


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