CHARGE syndrome and related disorders:A mechanistic link

CHARGE syndrome is an autosomal dominant malformation disorder caused by pathogenic variants in the chromatin remodeler CHD7. Affected are craniofacial structures, cranial nerves and multiple organ systems. Depending on the combination of malformations present, its distinction from other congenital disorders can be challenging. To gain a better insight into the regulatory disturbances in CHARGE syndrome, we performed RNA-Seq analysis on blood samples of 19 children with CHARGE syndrome and a confirmed disease-causing CHD7 variant in comparison to healthy control children. Our analysis revealed a distinct CHARGE syndrome pattern with downregulation of genes that are linked to disorders described to mimic the CHARGE phenotype, i.e. KMT2D and KDM6A (Kabuki syndrome), EP300 and CREBBP (Rubinstein-Taybi syndrome) and ARID1A and ARID1B (Coffin-Siris syndrome). Furthermore, by performing protein-protein interaction studies using co-immunoprecipitation, direct yeast-two hybrid and in situ proximity ligation assays, we could demonstrate an interplay between CHD7, KMT2D, KDM6A and EP300. In summary, our data demonstrate a mechanistic and regulatory link between the developmental disorders CHARGE-, Kabuki- and Rubinstein Taybi-syndrome providing an explanation for the overlapping phenotypes

Functional analysis of PTPN11 gene product SHP2 and of PTPN11 mutants causing Noonan Syndrome

Das Noonan-Syndrom (NS) [OMIM 163950] ist ein komplexes Fehlbildungssyndrom, das durch ein charakteristisches Gesicht mit Hypertelorismus und Ptosis, großen und tief sitzenden Ohren, Kleinwuchs, leichter geistiger Behinderung, Kryptorchismus und verschiedene Herzfehlbildungen (vor allem Pulmonalstenosen und hypertrophische Kardiomyopathie) gekennzeichnet ist. NS ist eine relativ häufige Erkrankung mit einem Vorkommen von 1:1000-2500 pro Lebendgeburt. Bei ca. 40-50% der Noonan-Patienten können missense Mutationen im PTPN11-Gen diagnostiziert werden. PTPN11-Mutationen können auch bei der allelische Variante von NS, dem LEOPARD-Syndrom (LS) gefunden werden. PTPN11 kodiert für die Nichtrezeptor Protein-Tyrosin-Phosphatase SHP2, die zwei Src-homology-2 (SH2) Domänen und eine Phosphatase-Domäne besitzt. Die N-terminale SH2-Domäne (N-SH2) ist ein konformativer Schalter: entweder interagiert N-SH2 mit der Phosphatase-Domäne (PTP) und hemmt diese, oder sie bindet an ein Phosphotyrosin-Motiv von Signalpartnern (z.B. Gab1) und lässt die Phosphatase-Domäne frei und aktiv. Alle bisher gefundenen Mutationen in PTPN11 verhindern die Bindung zwischen N-SH2 und PTP, was zu einer Überaktivität der Phosphatase führt.Im Rahmen der vorliegenden Arbeit sollten drei Aspekte untersucht werden. Im ersten Teil der Arbeit stand die Untersuchung unbekannter Ursachen des NS im Vordergrund. Sowohl die Mutationen im PTPN11-Promotor als auch große Deletionen wurden als fragliche Ursachen für das NS in Betracht gezogen. Der zweite Teil der Arbeit konzentrierte sich auf die Bestimmung der Phosphatase-Aktivität von SHP2-Varianten in vitro mit Hilfe eines SOCS1-Luciferase-Assays. Bei gain of function bot sich der Versuch der allelspezifischen Inhibition von PTPN11-Mutanten mit Hilfe der RNAi-Technik an. Schließlich sollte ein Mausmodell für das NS und das LS etabliert werden, da es zu Beginn dieser Arbeit noch kein Mausmodell gab

Periodic expression of Kv10.1 driven by pRb/E2F1 contributes to G2/M progression of cancer and non-transformed cells

<p>Progression of cell cycle is associated with changes in K⁺ channel expression and activity. In this study, we report that Kv10.1, a K⁺ channel that increases cell proliferation and tumor growth, is regulated at the transcriptional level by the pRb/E2F1 pathway. De-repression of E2F1 by HPV-E7 oncoprotein leads to increased expression of Kv10.1. In proliferating cells, E2F1 transcription factor binds directly to the Kv10.1 promoter during (or close to) G2/M, resulting in transient expression of the channel. Importantly, this happens not only in cancer cells but also in non-transformed cells. Lack of Kv10.1 in both cancer and non-transformed cells resulted in prolonged G2/M phase, as indicated by phosphorylation of Cdk1 (Y15) and sustained pRb hyperphosphorylation. Our results strongly suggest that Kv10.1 expression is coupled to cell cycle progression and facilitates G2/M progression in both healthy and tumor cells.</p

De novo mutations in FBRSL1 cause a novel recognizable malformation and intellectual disability syndrome

We report truncating de novo variants in specific exons of FBRSL1 in three unrelated children with an overlapping syndromic phenotype with respiratory insufficiency, postnatal growth restriction, microcephaly, global developmental delay and other malformations. The function of FBRSL1 is largely unknown. Interestingly, mutations in the FBRSL1 paralogue AUTS2 lead to an intellectual disability syndrome (AUTS2 syndrome). We determined human FBRSL1 transcripts and describe protein-coding forms by Western blot analysis as well as the cellular localization by immunocytochemistry stainings. All detected mutations affect the two short N-terminal isoforms, which show a ubiquitous expression in fetal tissues. Next, we performed a Fbrsl1 knockdown in Xenopus laevis embryos to explore the role of Fbrsl1 during development and detected craniofacial abnormalities and a disturbance in neurite outgrowth. The aberrant phenotype in Xenopus laevis embryos could be rescued with a human N-terminal isoform, while the long isoform and the N-terminal isoform containing the mutation p.Gln163* isolated from a patient could not rescue the craniofacial defects caused by Fbrsl1 depletion. Based on these data, we propose that the disruption of the validated N-terminal isoforms of FBRSL1 at critical timepoints during embryogenesis leads to a hitherto undescribed complex neurodevelopmental syndrome

μCT of <i>ex-vivo</i> stained mouse hearts and embryos enables a precise match between 3D virtual histology, classical histology and immunochemistry

<div><p>The small size of the adult and developing mouse heart poses a great challenge for imaging in preclinical research. The aim of the study was to establish a phosphotungstic acid (PTA) ex-vivo staining approach that efficiently enhances the x-ray attenuation of soft-tissue to allow high resolution 3D visualization of mouse hearts by synchrotron radiation based μCT (SRμCT) and classical μCT. We demonstrate that SRμCT of PTA stained mouse hearts ex-vivo allows imaging of the cardiac atrium, ventricles, myocardium especially its fibre structure and vessel walls in great detail and furthermore enables the depiction of growth and anatomical changes during distinct developmental stages of hearts in mouse embryos. Our x-ray based virtual histology approach is not limited to SRμCT as it does not require monochromatic and/or coherent x-ray sources and even more importantly can be combined with conventional histological procedures. Furthermore, it permits volumetric measurements as we show for the assessment of the plaque volumes in the aortic valve region of mice from an ApoE-/- mouse model. Subsequent, Masson-Goldner trichrome staining of paraffin sections of PTA stained samples revealed intact collagen and muscle fibres and positive staining of CD31 on endothelial cells by immunohistochemistry illustrates that our approach does not prevent immunochemistry analysis. The feasibility to scan hearts already embedded in paraffin ensured a 100% correlation between virtual cut sections of the CT data sets and histological heart sections of the same sample and may allow in future guiding the cutting process to specific regions of interest. In summary, since our CT based virtual histology approach is a powerful tool for the 3D depiction of morphological alterations in hearts and embryos in high resolution and can be combined with classical histological analysis it may be used in preclinical research to unravel structural alterations of various heart diseases.</p></div

Behavioural and functional characterization of Kv10.1 (Eag1) knockout mice

Kv10.1 (Eag1), member of the Kv10 family of voltage-gated potassium channels, is preferentially expressed in adult brain. The aim of the present study was to unravel the functional role of Kv10.1 in the brain by generating knockout mice, where the voltage sensor and pore region of Kv10.1 were removed to render non-functional proteins through deletion of exon 7 of the KCNH1 gene using the ‘3 Lox P strategy’. Kv10.1-deficient mice show no obvious alterations during embryogenesis and develop normally to adulthood; cortex, hippocampus and cerebellum appear anatomically normal. Other tests, including general health screen, sensorimotor functioning and gating, anxiety, social behaviour, learning and memory did not show any functional aberrations in Kv10.1 null mice. Kv10.1 null mice display mild hyperactivity and longer-lasting haloperidol-induced catalepsy, but there was no difference between genotypes in amphetamine sensitization and withdrawal, reactivity to apomorphine and haloperidol in the prepulse inhibition tests or to antidepressants in the haloperidol-induced catalepsy. Furthermore, electrical properties of Kv10.1 in cerebellar Purkinje cells did not show any difference between genotypes. Bearing in mind that Kv10.1 is overexpressed in over 70% of all human tumours and that its inhibition leads to a reduced tumour cell proliferation, the fact that deletion of Kv10.1 does not show a marked phenotype is a prerequisite for utilizing Kv10.1 blocking and/or reduction techniques, such as siRNA, to treat cancer

Sema3a plays a role in the pathogenesis of CHARGE syndrome

CHARGE syndrome is an autosomal dominant malformation disorder caused by heterozygous loss of function mutations in the chromatin remodeler CHD7. Chd7 regulates the expression of Sema3a, which also contributes to the pathogenesis of Kallmann syndrome, a heterogeneous condition with the typical features hypogonadotropic hypogonadism and an impaired sense of smell. Both features are common in CHARGE syndrome suggesting that SEMA3A may provide a genetic link between these syndromes. Indeed, we find evidence that SEMA3A plays a role in the pathogenesis of CHARGE syndrome. First, Chd7 is enriched at the Sema3a promotor in neural crest cells and loss of function of Chd7 inhibits Sema3a expression. Second, using a Xenopus CHARGE model, we show that human SEMA3A rescues Chd7 loss of function. Third, to elucidate if SEMA3A mutations in addition to CHD7 mutations also contribute to the severity of the CHARGE phenotype, we screened 31 CHD7-positive patients and identified one patient with a heterozygous non-synonymous SEMA3A variant, c. 2002A> G (p. I668V). By analyzing protein expression and processing, we did not observe any differences of the p. I668V variant compared with wild-type SEMA3A, while a pathogenic SEMA3A variant p. R66W recently described in a patient with Kallmann syndrome did affect protein secretion. Furthermore, the p. I668V variant, but not the pathogenic p. R66W variant, rescues Chd7 loss of function in Xenopus, indicating that the p. I668V variant is likely benign. Thus, SEMA3A is part of an epigenetic loop that plays a role in the pathogenesis of CHARGE syndrome, however, it seems not to act as a common direct modifier

Virtual cut sections through the heart region of PTA stained mouse embryos and postnatal mice.

<p>(A) The volume rendering of adult mouse heart and entire mouse embryo at E12 demonstrate that the adult mouse heart has approximately the same size as the entire mouse embryo at E12. Virtual transvers sections are shown for E12 (B), E15 (C) and E18 (D) and P0 (E) displaying details of the anatomical structures: the aorta (a) and lungs (l). As early as E12, the heart shows nearly the final shape and structure, as do other organs like the lung, and later only increase in size. Two different CT systems were used: classical μCT for E12 and SRμCT for E15, E18 and P0, demonstrating that with both CT techniques good and comparable results were obtained.</p