T-box genes and cardiac development.
BACKGROUND
T-box genes play roles in vertebrate gastrulation and in later organogenesis. Their existence in all metazoans examined so far indicates that this is an evolutionarily ancient gene family. Drosophila melanogaster has eight T-box genes, whereas Caenorhabditis elegans has 22. Mammals appear to have at least 18 T-box genes, comprising five subfamilies.


METHODS
A full range of cytological, developmental, molecular and genetic methodologies have recently been applied to the study of T-box genes.


RESULTS
Over the last 5 years, mutations in TBX1 and TBX5 have been implicated in two human disorders with haplo-insufficient cardiovascular phenotypes, DiGeorge/velocardiofacial syndrome and Holt-Oram ("heart-hand") syndrome. Interestingly, the number of T-box gene family members discovered to have cardiac or pharyngeal arch expression domains during vertebrate embryonic development has steadily grown. In addition, various Tbx5 loss-of-function models in organisms as distant as the mouse and zebrafish do indeed phenocopy Holt-Oram syndrome. Finally, the intriguing discovery earlier this year that a T-box gene is expressed in a subset of cardioblasts in D. melanogaster suggests that members of this gene family may have fundamental, conserved roles in cardiovascular pattern formation.


CONCLUSIONS
These developments prompted us to review the current understanding of the contribution of T-box genes to cardiovascular morphogenesis.
Ryan
Kenneth
K
Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Joseph Stokes Jr. Research Institute, Division of Cardiology, Abramson Research Center, Philadelphia, Pennsylvania, USA.
Chin
Alvin J
AJ
D000015:Abnormalities, Multiple / Q000196:embryology / Q000235:genetics; D000818:Animals; D017173:Caenorhabditis elegans / Q000196:embryology / Q000235:genetics; D002465:Cell Movement; D002642:Chick Embryo; D004062:DiGeorge Syndrome / Q000235:genetics; D029721:Drosophila Proteins / Q000235:genetics / Q000502:physiology; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics; D019143:Evolution, Molecular; D005318:Fetal Heart / Q000254:growth & development; D005326:Fetal Proteins; D018507:Gene Expression Regulation, Developmental; D006321:Heart / Q000196:embryology*; D006330:Heart Defects, Congenital / Q000196:embryology / Q000235:genetics*; D006801:Humans; D051379:Mice; D009024:Morphogenesis; D005810:Multigene Family; D020825:T-Box Domain Proteins / Q000145:classification / Q000172:deficiency / Q000235:genetics* / Q000502:physiology; D014714:Vertebrates / Q000196:embryology / Q000235:genetics; D000098908:Brachyury Protein
D029721:Drosophila Proteins; D005326:Fetal Proteins; D020825:T-Box Domain Proteins; D000098908:Brachyury Protein; C108625:TBX1 protein, human; C491573:Tbx1 protein, mouse