Gene replacement strategies to test the functional redundancy of basic helix-loop-helix transcription factor.
Basic helix-loop-helix (bHLH) transcription factors control developmental decisions for a wide range of embryonic cell types. Hand1 and Hand2 are closely related bHLH proteins that control cardiac, craniofacial, and limb development. Within the developing heart, Hand1 expression becomes restricted predominantly to the left ventricle, whereas Hand2 becomes restricted predominantly to the left ventricle, for which findings have shown each Hand factor to be necessary for normal chamber formation. Forced overexpression of Hand1 throughout the early developing heart induces abnormal interventricular septal development, with resulting pathogenesis of congenital heart defects. To investigate the potential transcriptional mechanisms involved in heart morphogenesis by Hand2, this study used a replacement targeting approach to knock Hand2 into the Hand1 locus and ectopically express one copy of Hand2 within the endogenous Hand1 expression domain in the developing hearts of transgenic mice. The findings show that high-percentage Hand1 ( Hand2 ) chimeras die at birth and exhibit a range of congenital heart defects. These findings suggest that Hand factors may act via unique transcriptional mechanisms mediated by bHLH factor partner choice, supporting the notion that alterations of Hand factor stoichiometry may be as deleterious to normal heart morphogenesis as Hand factor loss of function.
Riley Heart Research Center, Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, 1044 West Walnut Street, Room R4 W379, Indianapolis, IN 46202, USA.
Anthony B
AB
Firulli
Beth A
BA
Firulli
Jian
J
Wang
Rhonda H
RH
Rogers
Simon J
SJ
Conway
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics*; D002678:Chimera; D018507:Gene Expression Regulation, Developmental; D006321:Heart / Q000196:embryology*; D006330:Heart Defects, Congenital / Q000196:embryology / Q000235:genetics*; D006352:Heart Ventricles / Q000196:embryology / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics; D006801:Humans; D051379:Mice; D012150:Polymorphism, Restriction Fragment Length
D051792:Basic Helix-Loop-Helix Proteins; D018398:Homeodomain Proteins; C498765:HAND2 protein, human; C097341:helix-loop-helix protein, eHAND