Project description:Proper development of the specialized cardiac conduction system is crucial for function of the mature heart. Tools for isolation and in-vivo study of the conduction system are limited. The goal of this study was to identify pathways important for conduction system development. We generated a BAC transgenic mouse line, minKGFP, that marks the conduction system during embryogenesis and in adulthood. GFP is expressed in this line at high levels in conduction system myocardium (minkGFP high) and low levels in chamber myocardium (minKGFP low). We used this mouse line to isolate E10.5 conduction system cells, and performed transcriptional profiling on these cells to identify pathways with potential roles in specification of the developing cardiac conduction system.
Project description:The atrioventricular (AV) node is a recurrent source of potentially life-threatening arrhythmias. Nevertheless, limited data are available on its developmental control or molecular phenotype. We used a novel AV node-specific reporter mouse to gain insight into the gene programs determining the formation and phenotype of the AV node. In the transgenic reporter, green fluorescent protein (GFP) expression was driven by 160 kbp of Tbx3 and flanking sequences. GFP was selectively expressed in the AV canal of embryos, and in the AV node of adults, while all other Tbx3+ conduction system components, including the AV bundle, were devoid of GFP expression. Fluorescent AV nodal (Tbx3BAC-Egfp) and complementary working (NppaBAC336-Egfp) myocardial cell populations of E10.5 embryos and E17.5 fetuses were purified using fluorescence-activated cell sorting, and their expression profiles were assessed by microarray analysis. We constructed a comprehensive list of sodium, calcium, and potassium channels specific for the nodal or working myocard. Furthermore, the data revealed that the AV node and the working myocardium phenotypes diverge during development, but that the functional gene classes characteristic for both compartments are maintained. Interestingly, the AV node-specific gene repertoire consisted of multiple neurotrophic factors not yet appreciated to play a role in nodal development. These data present the first genome-wide transcription profiles of the AV node during development, providing valuable information concerning its molecular identity. Keywords: Tbx3, AV node, working myocardium, embryonic development, cardiac development, cardiac conduction system 24 samples: 6x working myocardium stage E10.5 (NppaBAC336-Egfp mice), 6x AV canal myocardium stage E10.5 (Tbx3BAC-Egfp mice), 6x working myocardium stage E17.5 (NppaBAC336-Egfp mice), 6x AV node myocardium stage E17.5 (Tbx3BAC-Egfp mice)
Project description:We created mice, which are deficient for Myc specifically in cardiac myocytes by crossing crossed Myc-floxed mice (Mycfl/fl) and MLC-2VCre/+ mice. Serial analysis of earlier stages of gestation revealed that Myc-deficient mice died prematurely at E13.5-14.5. Morphological analyses of E13.5 Myc-null embryos showed normal ventricular size and structure; however, decreased cardiac myocyte proliferation and increased apoptosis was observed. BrdU incorporation rates were also decreased significantly in Myc-null myocardium. Myc-null mice displayed a 3.67-fold increase in apoptotic cardiomyocytes by TUNEL assay. We examined global gene expression using oligonucleotide microarrays. Numerous genes involved in mitochondrial death pathways were dysregulated including Bnip3L and Birc2. Keywords: wildtype vs Myc-null
Project description:We created mice, which are deficient for Myc specifically in cardiac myocytes by crossing crossed Myc-floxed mice (Mycfl/fl) and MLC-2VCre/+ mice. Serial analysis of earlier stages of gestation revealed that Myc-deficient mice died prematurely at E13.5-14.5. Morphological analyses of E13.5 Myc-null embryos showed normal ventricular size and structure; however, decreased cardiac myocyte proliferation and increased apoptosis was observed. BrdU incorporation rates were also decreased significantly in Myc-null myocardium. Myc-null mice displayed a 3.67-fold increase in apoptotic cardiomyocytes by TUNEL assay. We examined global gene expression using oligonucleotide microarrays. Numerous genes involved in mitochondrial death pathways were dysregulated including Bnip3L and Birc2. Hearts were taken from wide type and Myc-null Mouse embryos at E13.5 under the dissecting scope. Cardiac myocyte RNA was isolated using TRIZOL®Reagent Total RNA (100 ng) was hybridized to the Sentrix® MouseRef-8 Expression BeadChip that contains probes for ~24,000 transcripts. GeneChips were scanned using the Hewlett-Packard GeneArray Scanner G2500A. The data were analyzed with Illumina Inc. BeadStudio version 1.5.0.34 and normalized by rank invariant method.
Project description:To characterize the genetic basis of hybrid male sterility in detail, we used a systems genetics approach, integrating mapping of gene expression traits with sterility phenotypes and QTL. We measured genome-wide testis expression in 305 male F2s from a cross between wild-derived inbred strains of M. musculus musculus and M. m. domesticus. We identified several thousand cis- and trans-acting QTL contributing to expression variation (eQTL). Many trans eQTL cluster into eleven ‘hotspots,’ seven of which co-localize with QTL for sterility phenotypes identified in the cross. The number and clustering of trans eQTL - but not cis eQTL - were substantially lower when mapping was restricted to a ‘fertile’ subset of mice, providing evidence that trans eQTL hotspots are related to sterility. Functional annotation of transcripts with eQTL provides insights into the biological processes disrupted by sterility loci and guides prioritization of candidate genes. Using a conditional mapping approach, we identified eQTL dependent on interactions between loci, revealing a complex system of epistasis. Our results illuminate established patterns, including the role of the X chromosome in hybrid sterility.
Project description:PGCs undergo two distinct stages of demethylation before reaching a hypomethylated ground state at E13.5. Stage 1 occurs between E7.25- E9.5 in which PGCs experience a global loss of cytosine methylation. However, discreet loci escape this global loss of methylation and between E10.5-E13.5, stage 2 of demethylation takes place. In this stage these loci are targeted by Tet1 and Tet2 leading to the loss of the remaining methylation and resulting in the epigenetic ground state. Our data shows that Dnmt1 is responsible for maintaining the methylation of loci that escape stage 1 demethylation, and that it functions in a UHRF1 independent manner. Our data further demonstrates that when these loci lose methylation prior to stage 2 it results in early activation of the meiotic program, which leads to precocious differentiation of the germ line resulting in a decreased pool of PGCs in the embryo and subsequent infertility in adult mice.
Project description:Introgressed variants from other species can be an important source of genetic variation because they may arise rapidly, can include multiple mutations on a single haplotype, and have often been pretested by selection in the species of origin. Although introgressed alleles are generally deleterious, several studies have reported introgression as the source of adaptive alleles-including the rodenticide-resistant variant of Vkorc1 that introgressed from Mus spretus into European populations of Mus musculus domesticus. Here, we conducted bidirectional genome scans to characterize introgressed regions into one wild population of M. spretus from Spain and three wild populations of M. m. domesticus from France, Germany, and Iran. Despite the fact that these species show considerable intrinsic postzygotic reproductive isolation, introgression was observed in all individuals, including in the M. musculus reference genome (GRCm38). Mus spretus individuals had a greater proportion of introgression compared with M. m. domesticus, and within M. m. domesticus, the proportion of introgression decreased with geographic distance from the area of sympatry. Introgression was observed on all autosomes for both species, but not on the X-chromosome in M. m. domesticus, consistent with known X-linked hybrid sterility and inviability genes that have been mapped to the M. spretus X-chromosome. Tract lengths were generally short with a few outliers of up to 2.7 Mb. Interestingly, the longest introgressed tracts were in olfactory receptor regions, and introgressed tracts were significantly enriched for olfactory receptor genes in both species, suggesting that introgression may be a source of functional novelty even between species with high barriers to gene flow.
Project description:Rationale: The atrioventricular conduction system controls ventricular activation and is delineated by expression of Tbx3. Genome-wide association studies identified genetic variants near TBX3 associated with conduction velocities (PR interval and QRS duration), suggesting minor changes in TBX3 dose affect conduction system function. Objective: To assess whether and how Tbx3 dose reduction affects the integrity of the atrioventricular conduction system. Methods and Results: Electrocardiograms revealed a PR interval shortening and prolonged QT interval and QRS duration in heterozygous Tbx3 mutants compared to wild-types. We observed that the atrioventricular bundle and proximal bundle branches of Tbx3+/- mice after birth became hypoplastic, whereas the size of the atrioventricular node was not affected. The transcriptomes of wild-type and Tbx3+/- atrioventricular nodes were analyzed using BAC-Tbx3-Egfp mice enabling specific isolation of the atrioventricular node by laser capture microdissection followed by RNA-sequencing. Hundreds of genes were slightly but consistently deregulated. Cross-referencing with transcriptome data of isolated cardiomyocytes of the conduction system and chamber myocardium derived from Tbx3+/Venus;BAC-Nppb-Katushka hearts revealed that a set of chamber-enriched genes, including Kcne1 (MinK), Ryr2, and Scn5a, were upregulated in Tbx3+/- atrioventricular nodes, whereas conduction system-enriched genes, including Hcn4 and Cacna2d2, were downregulated. We performed ATAC-sequencing on purified fetal Tbx3+ atrioventricular cardiomyocytes to identify potential atrioventricular-specific regulatory DNA elements on a genome-wide scale, and identified regulatory elements mediating the Tbx3-dependent regulation of Ryr2 and other target genes in the atrioventricular node. Conclusions: Tbx3 dose reduction results in deregulation of a large number of genes affecting the electrical properties of the atrioventricular node and causes failure to maintain the structural integrity of the atrioventricular bundle. These data provide a mechanism underlying differences in PR interval and QRS duration in individuals carrying associated variants in the TBX3 locus.