The pattern of congenital heart defects arising from reduced Tbx5 expression is altered in a Down syndrome mouse model

Renita C Polk,Huiqing Li,Sally A Camper,Ivan P Moskowitz,Peter Gergics,Roger H Reeves,Jeffrey D Steimle

doi:10.1186/s12861-015-0080-y

Abstract

BackgroundNearly half of all individuals with Down Syndrome (DS) have some type of congenital heart defect (CHD), suggesting that DS sensitizes to CHD but does not cause it. We used a common mouse model of DS, the Ts65Dn mouse, to study the contribution of Tbx5, a known modifier of CHD, to heart defects on a trisomic backgroun. Mice that were heterozygous for a Tbx5 null allele were crossed with Ts65Dn mice. Thoraxes of progeny were fixed in 10% formalin, embedded in paraffin, and sectioned for analysis of CHD. Gene expression in embryonic hearts was examined by quantitative PCR and in situ hybridization. A TBX5 DNA binding site was verified by luciferase assays.MethodsMice that were heterozygous for a Tbx5 null allele were crossed with Ts65Dn mice. Thoraxes of progeny were fixed in 10 % formalin, embedded in paraffin, and sectioned for analysis of CHD. Gene expression in embryonic hearts was examined by quantitative PCR and in situ hybridization. A TBX5 DNA binding site was verified by luciferase assays.ResultsWe crossed mice that were heterozygous for a Tbx5 null allele with Ts65Dn mice. Mice that were trisomic and carried the Tbx5 mutation (Ts65Dn;Tbx5+/−) had a significantly increased incidence of overriding aorta compared to their euploid littermates. Ts65Dn;Tbx5+/− mice also showed reduced expression of Pitx2, a molecular marker for the left atrium. Transcript levels of the trisomic Adamts1 gene were decreased in Tbx5+/− mice compared to their euploid littermates. Evidence of a valid binding site for TBX5 upstream of the trisomic Adamts1 locus was also shown.ConclusionHaploinsufficiency of Tbx5 and trisomy affects alignment of the aorta and this effect may stem from deviations from normal left-right patterning in the heart. We have unveiled a previously unknown interaction between the Tbx5 gene and trisomy, suggesting a connection between Tbx5 and trisomic genes important during heart development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12861-015-0080-y) contains supplementary material, which is available to authorized users.

Highlights

Half of all individuals with Down Syndrome (DS) have some type of congenital heart defect (CHD), suggesting that DS sensitizes to CHD but does not cause it
Attempts to identify genes predisposing to CHD in DS have understandably focused on Human chromosome 21 (Hsa21), while there has been little consideration of disomic modifiers that may contribute to this increased risk
Viability of Tbx5+/− mice is dependent on genetic background Crosses between between Ts65Dn females (B6).Tbx5+/− male mice and B6C3.Ts65Dn females were established to examine the role of Tbx5 as a Frequency of Tbx5+/− genotype

Summary

Introduction

Half of all individuals with Down Syndrome (DS) have some type of congenital heart defect (CHD), suggesting that DS sensitizes to CHD but does not cause it. We used a common mouse model of DS, the Ts65Dn mouse, to study the contribution of Tbx, a known modifier of CHD, to heart defects on a trisomic backgroun. Atrioventricular septal defect (AVSD) occurs in about 20 % of people with DS, a frequency about 2000-fold higher than in the population at large [8]. Since half of those with DS have a normal heart, additional genetic and environmental factors must interact with DS to cause CHD. Trisomy can be thought of as a genetically sensitizing condition that de-stabilizes normal heart development, unveiling roles of disomic modifiers of CHD [8, 9]. Attempts to identify genes predisposing to CHD in DS have understandably focused on Hsa, while there has been little consideration of disomic modifiers that may contribute to this increased risk

Methods

Results

Conclusion