TBX5 mutations in non-Holt-Oram syndrome (HOS) malformed heart: (Abstract, Fulltext online)

The T-box transcription factor Tbx5 is important in mammalian cardiac development. Mutations in the human TBX5 gene cause Holt-Oram syndrome (HOS), a disorder characterized by heart and upper limb deformities. To determine the role of TBX5 in non-HOS patients with complex cardiac malformations, we analyzed 68 explanted hearts from unrelated patients with various cardiac abnormalities including atrial (ASD), ventricular (VSD) and atrioventricular septal defects (AVSD). Direct sequencing detected nine mutations in diseased cardiac tissues of patients, eight of which are novel. Six mutations would affect amino acids in the T-domain, and one (c.236C>T, p.Ala79Val) is within the recently identified nuclear localization signal (NLS1) region. Further, mutations were found in patients with ASD and AVSD, but not with VSD; and mutations were absent in normal heart tissue of same patients, thus indicating somatic origin. Our results suggest a possible role of somatically occurring TBX5 mutations in congenital heart disease. We show for the first time TBX5 mutations in non-HOS associated cardiac malformations and we identified a novel missense mutation that would impact nuclear localization of TBX5

Genetic analysis of cardiac-specific transcription factors reveals insight into congenital heart disease

Heart development is complex and requires the sequential and timely interplay of regulatory master proteins, notably several transcription factors. Germline mutations in the human transcription factor genes such as NKX2-5, TBX5 and GATA4 are associated with cardiac anomalies. Familial cases so far studied have different mutations and no mutation can be associated with a specific clinical phenotype. Many cases of CHD come from unaffected family members. We searched for sequence alterations in cardiac specific transcription factor genes that would lead to loss-of-function of the protein in 68 malformed hearts from the Leipzig heart collection. By direct DNA sequencing, we obtained mutations in several transcription factors e.g. NKX2-5, TBX5 and GATA4 in the diseased heart tissues, which were mainly absent in normal heart tissues of the same CHD patients. We also observed multiple mutations in patients, multiple haplotypes, and detection of mutations in Down syndrome patients, all suggesting somatic origin of mutations and genomic instability in the diseased cardiac tissues of patients with CHD. Somatic mutations may provide an alternate mechanism of disease

Functional dissection of sequence-specific NKX2-5 DNA binding domain mutations associated with human heart septation defects using a yeast-based system

Human heart development requires an orderly coordination of transcriptional programs, with the homeodomain protein NKX2-5 being one of the key transcription factors required for the differentiation of mesodermal progenitor cells. Indeed, lack of Nkx2-5 in mice arrests heart development prior to looping, resulting in embryonic lethality. There are 28 germline NKX2-5 mutations identified in humans that are associated with congenital heart disease, and we recently reported multiple somatic mutations in patients with complex cardiac malformations. To address the functional consequences of single and multiple mutations of NKX2-5, we developed a functional assay in the budding yeast Saccharomyces cerevisiae, which could determine transactivation capacity and specificity of expressed NKX2-5 alleles towards targeted response element (RE) sequences. We focused on mutants of the third helix, which provides DNA binding specificity, and characterized mutations that were highly associated with either ventricular (VSD) or atrioventricular (AVSD) septal defects. Individual mutants exhibited partial to complete loss of function and differences in transactivation capacity between the various REs. The mutants also exhibited gene dosage rather than dominant effects on transcription. Surprisingly, all AVSD patients (22/23) had a single K183E mutation in the DNA binding domain, which resulted in transcriptional inactivation. None of the VSD patients had this mutation; yet 14/29 had at least one mutation in the third helix leading to either inactivation or reduction of NKX2-5 transactivation. Therefore, mutations of somatic origin in the binding domains of NKX2-5 were associated specifically with AVSD or VSD and resulted in loss of protein function

BAC-derived diagnostic markers for sex determination in asparagus

A HindIII BAC (bacterial artificial chromosome) library of asparagus (Asparagus officinalis L.) was established from a single male plant homozygous for the male flowering gene (MM). The library represents approximately 5.5 haploid genome equivalents with an average insert size of 82 kb. A subset of the library (2.6 haploid genome equivalents) was arranged into DNA pools. Using nine sex-linked amplified fragment length polymorphism (AFLP) and two sequence-tagged site (STS) markers, 13 different BAC clones were identified from this part of the library. The BACs were arranged into a first-generation physical map around the sex locus. Four PCR-derived markers were developed from the BAC ends, one of which could be scored in a co-dominant way. Using a mapping population of 802 plants we mapped the BAC-derived markers to the same position close to the M gene as the corresponding AFLP and STS markers. The markers are useful for further chromosome walking studies and as diagnos tic markers for selecting male plants homozygous for the M gene