Familial multiple discoid fibromas is linked to a locus on chromosome 5 including the FNIP1 gene.

Previously, we reported a series of families presenting with trichodiscomas, inherited in an autosomal dominant pattern. The phenotype was named familial multiple discoid fibromas (FMDF). The genetic cause of FMDF remained unknown so far. Trichodiscomas are skin lesions previously reported to be part of the same spectrum as the fibrofolliculoma observed in Birt-Hogg-Dubé syndrome (BHD), an inherited disease caused by pathogenic variants in the FLCN gene. Given the clinical and histological differences with BHD and the exclusion of linkage with the FLCN locus, the phenotype was concluded to be distinct from BHD. We performed extensive clinical evaluations and genetic testing in ten families with FMDF. We identified a FNIP1 frameshift variant in nine families and genealogical studies showed common ancestry for eight families. Using whole exome sequencing, we identified six additional rare variants in the haplotype surrounding FNIP1, including a missense variant in the PDGFRB gene that was found to be present in all tested patients with FMDF. Genome-wide linkage analysis showed that the locus on chromosome 5 including FNIP1 was the only region reaching the maximal possible LOD score. We concluded that FMDF is linked to a haplotype on chromosome 5. Additional evaluations in families with FMDF are required to unravel the exact genetic cause underlying the phenotype. When evaluating patients with multiple trichodisomas without a pathogenic variant in the FLCN gene, further genetic testing is warranted and can include analysis of the haplotype on chromosome 5.

Efficiency Correction Is Required for Accurate Quantitative PCR Analysis and Reporting.

BACKGROUND: Quantitative PCR (qPCR) aims to measure the DNA or RNA concentration in diagnostic and biological samples based on the quantification cycle (Cq) value observed in the amplification curves. Results of qPCR experiments are regularly calculated as if all assays are 100% efficient or reported as just Cq, ΔCq, or ΔΔCq values. CONTENTS: When the reaction shows specific amplification, it should be deemed to be positive, regardless of the observed Cq. Because the Cq is highly dependent on amplification efficiency that can vary among targets and samples, accurate calculation of the target quantity and relative gene expression requires that the actual amplification efficiency be taken into account in the analysis and reports. PCR efficiency is frequently derived from standard curves, but this approach is affected by dilution errors and hampered by properties of the standard and the diluent. These factors affect accurate quantification of clinical and biological samples used in diagnostic applications and collected in challenging conditions. PCR efficiencies determined from individual amplification curves avoid these confounders. To obtain unbiased efficiency-corrected results, we recommend absolute quantification with a single undiluted calibrator with a known target concentration and efficiency values derived from the amplification curves of the calibrator and the unknown samples. SUMMARY: For meaningful diagnostics or biological interpretation, the reported results of qPCR experiments should be efficiency corrected. To avoid ambiguity, the Minimal Information for Publications on Quantitative Real-Time PCR Experiments (MIQE) guidelines checklist should be extended to require the methods that were used (1) to determine the PCR efficiency and (2) to calculate the reported target quantity and relative gene expression value.

Profiling proliferative cells and their progeny in damaged murine hearts.

The significance of cardiac stem cell (CSC) populations for cardiac regeneration remains disputed. Here, we apply the most direct definition of stem cell function (the ability to replace lost tissue through cell division) to interrogate the existence of CSCs. By single-cell mRNA sequencing and genetic lineage tracing using two Ki67 knockin mouse models, we map all proliferating cells and their progeny in homoeostatic and regenerating murine hearts. Cycling cardiomyocytes were only robustly observed in the early postnatal growth phase, while cycling cells in homoeostatic and damaged adult myocardium represented various noncardiomyocyte cell types. Proliferative postdamage fibroblasts expressing follistatin-like protein 1 (FSTL1) closely resemble neonatal cardiac fibroblasts and form the fibrotic scar. Genetic deletion of Fstl1 in cardiac fibroblasts results in postdamage cardiac rupture. We find no evidence for the existence of a quiescent CSC population, for transdifferentiation of other cell types toward cardiomyocytes, or for proliferation of significant numbers of cardiomyocytes in response to cardiac injury.

Removal of artifact bias from qPCR results using DNA melting curve analysis.

Quantitative PCR (qPCR) allows the precise measurement of DNA concentrations and is generally considered to be straightforward and trouble free. However, analyses using validated Sybr Green I-based assays regularly amplify both the correct product and an artifact. Amplification of more than 1 product can be recognized when melting curve analysis is performed after the qPCR. Currently, such reactions need to be excluded from further analysis because the quantification result is considered meaningless. However, when the fraction of the fluorescence associated with the correct product can be determined, the quantitative result of the qPCR analysis can be corrected. The main assumptions of this correction model are: 1) the melting peak of the correct product can be identified, 2) the PCR efficiencies of all amplified products are similar, 3) the relative size of the melting peaks reflects the relative concentrations of the products, and 4) the relative concentrations do not change as the reaction reaches plateau. These assumptions were validated in a series of model experiments. The results show that the quantitative results can be corrected. Implementation of a correction for the presence of artifact amplification in the analysis of qPCR data leads to more reliable quantitative results in qPCR experiments.-Ruijter, J. M., Ruiz-Villalba, A., van den Hoff, A. J. J., Gunst, Q. D., Wittwer, C. T., van den Hoff, M. J. B. Removal of artifact bias from qPCR results using DNA melting curve analysis.

Deletion of Fstl1 (Follistatin-Like 1) From the Endocardial/Endothelial Lineage Causes Mitral Valve Disease.

OBJECTIVE: Fstl1 (Follistatin-like 1) is a secreted protein that is expressed in the atrioventricular valves throughout embryonic development, postnatal maturation, and adulthood. In this study, we investigated the loss of Fstl1 in the endocardium/endothelium and their derived cells. APPROACH AND RESULTS: We conditionally ablated Fstl1 from the endocardial lineage using a transgenic Tie2-Cre mouse model. These mice showed a sustained Bmp and Tgfß signaling after birth. This resulted in ongoing proliferation and endocardial-to-mesenchymal transition and ultimately in deformed nonfunctional mitral valves and a hypertrophic dilated heart. Echocardiographic and electrocardiographic analyses revealed that loss of Fstl1 leads to mitral regurgitation and left ventricular diastolic dysfunction. Cardiac function gradually deteriorated resulting in heart failure with preserved ejection fraction and death of the mice between 2 and 4 weeks after birth. CONCLUSIONS: We report on a mouse model in which deletion of Fstl1 from the endocardial/endothelial lineage results in deformed mitral valves, which cause regurgitation, heart failure, and early cardiac death. The findings provide a potential molecular target for the clinical research into myxomatous mitral valve disease.

WT1 regulates the expression of inhibitory chemokines during heart development.

The embryonic epicardium is an important source of cardiovascular precursor cells and paracrine factors that are required for adequate heart formation. Signaling pathways regulated by WT1 that promote heart development have started to be described; however, there is little information on signaling pathways regulated by WT1 that could act in a negative manner. Transcriptome analysis of Wt1KO epicardial cells reveals an unexpected role for WT1 in repressing the expression of interferon-regulated genes that could be involved in a negative regulation of heart morphogenesis. Here, we showed that WT1 is required to repress the expression of the chemokines Ccl5 and Cxcl10 in epicardial cells. We observed an inverse correlation of Wt1 and the expression of Cxcl10 and Ccl5 during epicardium development. Chemokine receptor analyses of hearts from Wt1(gfp/+) mice demonstrate the differential expression of their chemokine receptors in GFP(+) epicardial enriched cells and GFP(-) cells. Functional assays demonstrate that CXCL10 and CCL5 inhibit epicardial cells migration and the proliferation of cardiomyocytes respectively. WT1 regulates the expression levels of Cxcl10 and Ccl5 in epicardial cells directly and indirectly through increasing the levels of IRF7. As epicardial cell reactivation after a myocardial damage is linked with WT1 expression, the present work has potential implications in adult heart repair.

Human embryonic and fetal biobanking: Establishing the Dutch Fetal Biobank and a framework for standardization.

Recent studies of human embryos and fetuses have advanced our understanding not only of basic biology but also of health and disease, through a combination of detailed three-dimensional (3D) morphology and processes such as gene expression, cellular decision-making and differentiation, and epigenetics during the various phases of human development and growth. Large-scale research initiatives focusing on these topics have been initiated during the last decade, all of which depend on biobanks that provide high-quality images of human embryonic and fetal morphology, as well as on high-quality collections of tissue samples that are obtained and stored appropriately. In this perspective, we describe our experience in establishing the Dutch Fetal Biobank to present the framework and workflow of the biobank, provide a brief discussion of the main legal and ethical aspects involved in establishing a pre-natal tissue bank, and present the preliminary data on the first 329 donated specimens.

Considerations for Measurement of Embryonic Organ Growth.

Organogenesis is a complex coordinated process of cell proliferation, growth, migration, and apoptosis. Differential growth rates, particularly during cardiogenesis, play a role in establishing morphology. Studies using stereological and cell sorting methods derive averages of morphogenetic parameters for an organ. To understand tissue composition and differential growth, the researcher must determine a number of morphogenetic parameters in the developing organ. Such measurements require sectioning to enable identification of organ borders, tissue components and cell types, three-dimensional (3D)-reconstruction of sections to visualize morphology and a 3D-measurement scheme to build local morphogenetic information. Although thick the section confocal microscopy partially solves these issues, information loss at the section surface hampers the reconstruction of 3D morphology. Episcopic imaging provides the correct morphology but lacks histological procedures to identify multiple cell types. The 3D-measurement scheme is based on systematic sampling, with overlapping sample volumes, of the entire organ in the aligned image stack. For each sample volume, morphogenetic variables are calculated and results projected back to the cube (boxel) at the sample volume center. Boxel size determines spatial resolution of the final quantitative 3D-reconstruction whereas size of the sample volume determines the precision of the morphogenetic information. The methods described here can be used to measure tissue volume, proliferation and cell size, to determine contribution and distribution of cell types in a tissue and to display this information in a quantitative 3D-reconstruction. Anat Rec, 302:49-57, 2019. © 2018 Wiley Periodicals, Inc.

Amplification of nonspecific products in quantitative polymerase chain reactions (qPCR).

Quantitative PCR allows the precise measurement of DNA concentrations and is generally considered to be straightforward and trouble free. However, a survey with 93 validated assays for genes in the Wnt-pathway showed that the amplification of nonspecific products occurs frequently and is unrelated to Cq or PCR efficiency values. Titration experiments showed that the occurrence of low and high melting temperature artifacts was shown to be determined by annealing temperature, primer concentration and cDNA input. To explore the range of input variations that occur in the normal use of the Cre assay these conditions were mimicked in a complete two-way design of template -plasmid DNA- and non-template -mouse cDNA- concentrations. These experiments showed that the frequency of the amplification of the correct product and the artifact, as well as the valid quantification of the correct product, depended on the concentration of the non-template cDNA. This finding questions the interpretation of dilution series in which template as well as non-template concentrations are simultaneously decreasing. Repetition of this cDNA concentration experiment with other templates revealed that exact reproduction qPCR experiments was affected by the time it takes to complete the pipetting of a qPCR plate. Long bench times were observed to lead to significantly more artifacts. However, the measurement of artifact-associated fluorescence can be avoided by inclusion of a small heating step after the elongation phase in the amplification protocol. Taken together, this trouble-shooting journey showed that reliability and reproducibility of qPCR experiments not only depends on standardization and reporting of the biochemistry and technical aspects but also on hitherto neglected factors as sample dilution and waiting times in the laboratory work flow.

Reference genes for gene expression studies in the mouse heart.

To be accurate, quantitative Polymerase Chain Reaction (qPCR) studies require a set of stable reference genes for normalization. This is especially critical in cardiac research because of the diversity of the clinical and experimental conditions in the field. We analyzed the stability of previously described as potential reference genes in different subsets of cardiac tissues, each representing a different field in cardiac research. The qPCR dataset was based on 119 different tissue samples derived from cardiac development to pathology in mouse adult hearts. These samples were grouped into 47 tissue types. The stability of 9 candidate genes was analyzed in each of 12 experimental conditions comprising different groupings of these tissue types. Expression stability was determined with the geNorm module of qbase+. This analysis showed that different sets of two or three reference genes are required for analysis of qPCR data in different experimental conditions in murine cardiac research.

Endothelial follistatin-like-1 regulates the postnatal development of the pulmonary vasculature by modulating BMP/Smad signaling.

Bone morphogenetic protein (BMP) signaling regulates vascular smooth muscle maturation, endothelial cell proliferation, and tube formation. The endogenous BMP antagonist Follistatin-like 1 (Fstl1) is highly expressed in pulmonary vascular endothelium of the developing mouse lung, suggesting a role in pulmonary vascular formation and vascular homeostasis. The aim of this study was to investigate the role of Fstl1 in the pulmonary vascular endothelium. To this aim, Fstl1 was conditionally deleted from endothelial and endothelial-derived cells using Tie2-cre driven Fstl1-KO mice (Fstl1-eKO mice). Endothelial-specific Fstl1 deletion was postnatally lethal, as ∼70% of Fstl1-eKO mice died at three weeks after birth. Deletion of Fstl1 from endothelium resulted in a reduction of right ventricular output at three weeks after birth compared with controls. This was associated with pulmonary vascular remodeling, as the percentage of actin-positive small pulmonary vessels was increased at three weeks in Fstl1-eKO mice compared with controls. Endothelial deletion of Fstl1 resulted in activation of Smad1/5/8 signaling and increased BMP/Smad-regulated gene expression of Jagged1, Endoglin, and Gata2 at one week after birth compared with controls. In addition, potent vasoconstrictor Endothelin-1, the expression of which is driven by Gata2, was increased in expression, both on the mRNA and protein levels, at one week after birth compared with controls. At three weeks, Jagged1 was reduced in the Fstl1-eKO mice whereas Endoglin and Endothelin-1 were unchanged. In conclusion, loss of endothelial Fstl1 in the lung is associated with elevated BMP-regulated genes, impaired small pulmonary vascular remodeling, and decreased right ventricular output.

Cardiac regeneration from activated epicardium.

In contrast to lower vertebrates, the mammalian heart has a very limited regenerative capacity. Cardiomyocytes, lost after ischemia, are replaced by fibroblasts. Although the human heart is able to form new cardiomyocytes throughout its lifespan, the efficiency of this phenomenon is not enough to substitute sufficient myocardial mass after an infarction. In contrast, zebrafish hearts regenerate through epicardial activation and initiation of myocardial proliferation. With this study we obtain insights into the activation and cellular contribution of the mammalian epicardium in response to ischemia. In a mouse myocardial infarction model we analyzed the spatio-temporal changes in expression of embryonic epicardial, EMT, and stem cell markers and the contribution of cells of the Wt1-lineage to the infarcted area. Though the integrity of the epicardial layer overlaying the infarct is lost immediately after the induction of the ischemia, it was found to be regenerated at three days post infarction. In this regenerated epicardium, the embryonic gene program is transiently re-expressed as well as proliferation. Concomitant with this activation, Wt1-lineage positive subepicardial mesenchyme is formed until two weeks post-infarction. These mesenchymal cells replace the cardiomyocytes lost due to the ischemia and contribute to the fibroblast population, myofibroblasts and coronary endothelium in the infarct, and later also to the cardiomyocyte population. We show that in mice, as in lower vertebrates, an endogenous, epicardium-dependent regenerative response to injury is induced. Although this regenerative response leads to the formation of new cardiomyocytes, their number is insufficient in mice but sufficient in lower vertebrates to replace lost cardiomyocytes. These molecular and cellular analyses provide basic knowledge essential for investigations on the regeneration of the mammalian heart aiming at epicardium-derived cells.

Identifying the evolutionary building blocks of the cardiac conduction system.

The endothermic state of mammals and birds requires high heart rates to accommodate the high rates of oxygen consumption. These high heart rates are driven by very similar conduction systems consisting of an atrioventricular node that slows the electrical impulse and a His-Purkinje system that efficiently activates the ventricular chambers. While ectothermic vertebrates have similar contraction patterns, they do not possess anatomical evidence for a conduction system. This lack amongst extant ectotherms is surprising because mammals and birds evolved independently from reptile-like ancestors. Using conserved genetic markers, we found that the conduction system design of lizard (Anolis carolinensis and A. sagrei), frog (Xenopus laevis) and zebrafish (Danio rerio) adults is strikingly similar to that of embryos of mammals (mouse Mus musculus, and man) and chicken (Gallus gallus). Thus, in ectothermic adults, the slow conducting atrioventricular canal muscle is present, no fibrous insulating plane is formed, and the spongy ventricle serves the dual purpose of conduction and contraction. Optical mapping showed base-to-apex activation of the ventricles of the ectothermic animals, similar to the activation pattern of mammalian and avian embryonic ventricles and to the His-Purkinje systems of the formed hearts. Mammalian and avian ventricles uniquely develop thick compact walls and septum and, hence, form a discrete ventricular conduction system from the embryonic spongy ventricle. Our study uncovers the evolutionary building plan of heart and indicates that the building blocks of the conduction system of adult ectothermic vertebrates and embryos of endotherms are similar.