title: Analysis of a Hand1 hypomorphic allele reveals a critical threshold for embryonic viability.
abstract: Loss-of-function analysis of the basic helix-loop-helix (bHLH) transcription factor Hand1 indicates critical roles in development. In an effort to generate a Hand1 cDNA knock-in reporter mouse, we generated two hypomorphic alleles, which extend embryonic survival to between embryonic day (E) 10.5 and E12.5. Heart morphogenesis appears largely normal; however, hypomorphic mice display thin left ventricular myocardium and reduction in pharyngeal mesoderm. Caudal defects, large allantois, and thickened yolk sac are observed and consistent with systemic Hand1 gene deletion. Hand1 mRNA is expressed at 30% of wild-type littermates and known Hand1-dependent genes show intermediate expression compared with wild-type and Hand1 null mice. Interestingly, putative bHLH partners, Hand2 and Twist1, show altered expression in both Hand1 null and hypomorphic backgrounds and intercrossing the Hand1 hypomorphic mice onto the Hand2 systemic null background exacerbates the cardiac and lateral mesoderm phenotypes. Together, these data define a critical threshold of Hand1 expression that is necessary for embryonic survival.
authors.affiliation: Riley Heart Research Center, Herman B. Wells Center for Pediatric Research Division of Pediatrics Cardiology, Departments of Anatomy and Medical and Molecular Genetics, Indiana Medical School, Indianapolis, Indiana 46202-5225, USA.
authors.forename: Beth A
authors.initials: BA
authors.lastname: Firulli
authors.forename: David P
authors.initials: DP
authors.lastname: McConville
authors.forename: James S
authors.initials: JS
authors.lastname: Byers
authors.forename: Joshua W
authors.initials: JW
authors.lastname: Vincentz
authors.forename: Ralston M
authors.initials: RM
authors.lastname: Barnes
authors.forename: Anthony B
authors.initials: AB
authors.lastname: Firulli
mesh_terms: D000483:Alleles; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000378:metabolism*; D006321:Heart / Q000196:embryology; D015151:Immunoblotting; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D051379:Mice; D018345:Mice, Knockout; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; C095572:Hand1 protein, mouse; C498766:Hand2 protein, mouse