Project description:Left and Right phrenic nerves, which innervate the left and right diaphragm muscles, exhibit different innervation patterns. This left/right (L/R) asymmetry is established at the onset of innervation by a developmental program that requires Nodal. Phenotype analysis suggests that the cervical motoneurons, which innervate the diaphragm, have a L/R imprint that contributes to set the L/R asymmetries of innervation. We used microarray to analyze the expression profile of left and right cervical motoneurons before diaphragm innervation
Project description:Heterotaxy is a disorder characterized by severe congenital heart defects (CHDs) and abnormal left-right patterning in other thoracic or abdominal organs. Clinical and research-based genetic testing has previously focused on evaluation of coding variants to identify causes of CHDs, leaving non-coding causes of CHDs largely unknown. Variants in the transcription factor Zinc finger of the cerebellum 3 (ZIC3) cause X-linked heterotaxy. We identified an X-linked heterotaxy pedigree without a coding variant in ZIC3. Whole genome sequencing revealed a deep intronic variant (ZIC3 c.1224+3286A>G) predicted to alter RNA splicing. An in vitro minigene splicing assay confirmed the variant acts as a cryptic splice acceptor. CRISPR/Cas9 served to introduce the ZIC3 c.1224+3286A>G variant into human embryonic stem cells demonstrating pseudoexon inclusion caused by the variant. Surprisingly, Sanger sequencing of the resulting ZIC3 c.1224+3286A>G amplicons revealed several isoforms, many of which by-pass the normal coding sequence of the third exon of ZIC3, causing a disruption of a DNA binding domain and a nuclear localization signal. Short- and long-read mRNA sequencing confirmed these initial results and identified additional splicing patterns. Assessment of four isoforms determined abnormal functions in vitro and in vivo while treatment with a splice-blocking morpholino partially rescued ZIC3. These results demonstrate that pseudoexon inclusion in ZIC3 can cause heterotaxy and provide functional validation of non-coding disease causation. Our results suggest the importance of non-coding variants in heterotaxy and the need for improved methods to identify and classify non-coding variation that may contribute to CHDs.
Project description:Congenital heart disease (CHD) is the most common birth defect, yet its genetic causes continue to be obscure. Fibroblast growth factor receptor 4 (FGFR4) recently emerged in a large patient exome sequencing study as a candidate disease gene for CHD and specifically heterotaxy. In heterotaxy, patterning of the left-right (LR) body axis is compromised, frequently leading to defects in the heart's LR architecture and severe CHD. FGF ligands like FGF8 and FGF4 have been previously implicated in LR development with roles ranging from formation of the laterality organ [LR organizer (LRO)] to the transfer of asymmetry from the embryonic midline to the lateral plate mesoderm (LPM). However, much less is known about which FGF receptors (FGFRs) play a role in laterality. Here, we show that the candidate heterotaxy gene FGFR4 is essential for proper organ situs in Xenopus and that frogs depleted of fgfr4 display inverted cardiac and gut looping. Fgfr4 knockdown causes mispatterning of the LRO even before cilia on its surface initiate symmetry-breaking fluid flow, indicating a role in the earliest stages of LR development. Specifically, fgfr4 acts during gastrulation to pattern the paraxial mesoderm, which gives rise to the lateral pre-somitic portion of the LRO. Upon fgfr4 knockdown, the paraxial mesoderm is mispatterned in the gastrula and LRO, and crucial genes for symmetry breakage, like coco, xnr1, and gdf3 are subsequently absent from the lateral portions of the organizer. In summary, our data indicate that FGF signaling in mesodermal LRO progenitors defines cell fates essential for subsequent LR patterning.
Project description:The right and left atria have different susceptibilities towards developing arrhythmias, with left atrial arrhythmias more commonly observed. To study potential underlying causes of this difference between the two upper chambers of the heart, four human left-right atrial pairs were subjected to whole-genome expression analyses via next generation sequencing of small RNAs, including microRNAs (miRNAs), and polyA enriched mRNAs. Using a paired sample design, significant differences in gene expression were found between the left and right atria in both the poly-A and small RNA fractions. Hsa-miR-143 was the most highly expressed miRNA in the atria as quantified by RNA-seq. Gene expression differences established during development are retained into adulthood including that of PITX2 and BMP10. In addition ten novel non-coding RNAs were found to be differentially expressed between the left and right atrias .