Ofd1 controls dorso-ventral patterning and axoneme elongation during embryonic brain development

Histopathological effects of long-term exposure to realistic concentrations of cadmium in the hepatopancreas of Sparus aurata juveniles

In recent decades, cadmium has emerged as an environmental stressor in aquatic ecosystems due to its persistence and toxicity. It can enter water bodies from various natural and anthropogenic sources and, once introduced into aquatic systems, can accumulate in sediments and biota, leading to bioaccumulation and biomagnification in the food chain. For this reason, the effects of cadmium on aquatic life remain an area of ongoing research and concern. In this paper, a multidisciplinary approach was used to assess the effects of long-term exposure to an environmental concentration on the hepatopancreas of farmed juveniles of sea bream, Sparus aurata. After determining metal uptake, metallothionein production was assessed to gain insight into the organism's defence response. The effects were also assessed by histological and ultrastructural analyses. The results indicate that cadmium accumulates in the hepatopancreas at significant concentrations, inducing structural and functional damage. Despite the parallel increase in metallothioneins, fibrosis, alterations in carbohydrate distribution and endocrine disruption were also observed. These effects would decrease animal fitness although it did not translate into high mortality or reduced growth. This could depend on the fact that the animals were farmed, protected from the pressure deriving from having to search for food or escape from predators. Not to be underestimated is the return to humans, as this species is edible. Understanding the behaviour of cadmium in aquatic systems, its effects at different trophic levels and the potential risks to human health from the consumption of contaminated seafood would therefore be essential for informed environmental management and policy decisions.

IK is essentially involved in ciliogenesis as an upstream regulator of oral-facial-digital syndrome ciliopathy gene, ofd1

BACKGROUND

The cilia are microtubule-based organelles that protrude from the cell surface. Abnormalities in cilia result in various ciliopathies, including polycystic kidney disease (PKD), Bardet-Biedl syndrome (BBS), and oral-facial-digital syndrome type I (OFD1), which show genetic defects associated with cilia formation. Although an increasing number of human diseases is attributed to ciliary defects, the functions or regulatory mechanisms of several ciliopathy genes remain unclear. Because multi ciliated cells (MCCs) are especially deep in vivo, studying ciliogenesis is challenging. Here, we demonstrate that ik is essential for ciliogenesis in vivo.

RESULTS

In the absence of ik, zebrafish embryos showed various ciliopathy phenotypes, such as body curvature, abnormal otoliths, and cyst formation in the kidney. RNA sequencing analysis revealed that ik positively regulated ofd1 expression required for cilium assembly. In fact, depletion of ik resulted in the downregulation of ofd1 expression with ciliary defects, and these ciliary defects in ik mutants were rescued by restoring ofd1 expression. Interestingly, ik affected ciliogenesis particularly in the proximal tubule but not in the distal tubule in the kidney.

CONCLUSIONS

This study demonstrates the role of ik in ciliogenesis in vivo for the first time. Loss of ik in zebrafish embryos displays various ciliopathy phenotypes with abnormal ciliary morphology in ciliary tissues. Our findings on the ik-ofd1 axis provide new insights into the biological function of ik in clinical ciliopathy studies in humans.

Brain mosaicism of hedgehog signalling and other cilia genes in hypothalamic hamartoma

Hypothalamic hamartoma (HH) is a rare benign developmental brain lesion commonly associated with a well characterized epilepsy phenotype. Most individuals with HH are non-syndromic without additional developmental anomalies nor a family history of disease. Nonetheless, HH is a feature of Pallister-Hall (PHS) and Oro-Facial-Digital Type VI (OFD VI) syndromes, both characterized by additional developmental anomalies. Initial genetic of analysis HH began with syndromic HH, where germline inherited or de novo variants in GLI3, encoding a central transcription factor in the sonic hedgehog (Shh) signalling pathway, were identified in most individuals with PHS. Following these discoveries in syndromic HH, the hypothesis that post-zygotic mosaicism in related genes may underly non-syndromic HH was tested. We discuss the identified mosaic variants within individuals with non-syndromic HH, review the analytical methodologies and diagnostic yields, and explore understanding of the functional role of the implicated genes with respect to Shh signalling, and cilia development and function. We also outline future challenges in studying non-syndromic HH and suggest potential novel strategies to interrogate brain mosaicism in HH.

DOT1L activity affects neural stem cell division mode and reduces differentiation and ASNS expression

Cortical neurogenesis depends on the balance between self-renewal and differentiation of apical progenitors (APs). Here, we study the epigenetic control of AP's division mode by focusing on the enzymatic activity of the histone methyltransferase DOT1L. Combining lineage tracing with single-cell RNA sequencing of clonally related cells, we show at the cellular level that DOT1L inhibition increases neurogenesis driven by a shift of APs from asymmetric self-renewing to symmetric neurogenic consumptive divisions. At the molecular level, DOT1L activity prevents AP differentiation by promoting transcription of metabolic genes. Mechanistically, DOT1L inhibition reduces activity of an EZH2/PRC2 pathway, converging on increased expression of asparagine synthetase (ASNS), a microcephaly associated gene. Overexpression of ASNS in APs phenocopies DOT1L inhibition, and also increases neuronal differentiation of APs. Our data suggest that DOT1L activity/PRC2 crosstalk controls AP lineage progression by regulating asparagine metabolism.

Autistic Behavior as Novel Clinical Finding in OFD1 Syndrome

Orofaciodigital syndrome I (OFD1-MIM #311200) is a rare ciliopathy characterized by facial dysmorphism, oral cavity, digit, and brain malformations, and cognitive deficits. OFD1 syndrome is an X-linked dominant disorder reported mostly in females. The gene responsible for this condition, OFD1 centriole and centriolar satellite protein (OFD1), is involved in primary cilia formation and several cilia-independent biological processes. The functional and structural integrity of the cilia impacts critical brain development processes, explaining the broad range of neurodevelopmental anomalies in ciliopathy patients. As several psychiatric conditions, such as autism spectrum disorders (ASD) and schizophrenia, are neurodevelopmental in nature, their connections with cilia roles are worth exploring. Moreover, several cilia genes have been associated with behavioral disorders, such as autism. We report on a three-year-old girl with a complex phenotype that includes oral malformations, severe speech delay, dysmorphic features, developmental delay, autism, and bilateral periventricular nodular heterotopia, presenting a de novo pathogenic variant in the OFD1 gene. Furthermore, to the best of our knowledge, this is the first report of autistic behavior in a female patient with OFD1 syndrome. We propose that autistic behavior should be considered a potential feature of this syndrome and that active screening for early signs of autism might prove beneficial for OFD1 syndrome patients.

Primary Cilia Influence Progenitor Function during Cortical Development

Corticogenesis is an intricate process controlled temporally and spatially by many intrinsic and extrinsic factors. Alterations during this important process can lead to severe cortical malformations. Apical neuronal progenitors are essential cells able to self-amplify and also generate basal progenitors and/or neurons. Apical radial glia (aRG) are neuronal progenitors with a unique morphology. They have a long basal process acting as a support for neuronal migration to the cortical plate and a short apical process directed towards the ventricle from which protrudes a primary cilium. This antenna-like structure allows aRG to sense cues from the embryonic cerebrospinal fluid (eCSF) helping to maintain cell shape and to influence several key functions of aRG such as proliferation and differentiation. Centrosomes, major microtubule organising centres, are crucial for cilia formation. In this review, we focus on how primary cilia influence aRG function during cortical development and pathologies which may arise due to defects in this structure. Reporting and cataloguing a number of ciliary mutant models, we discuss the importance of primary cilia for aRG function and cortical development.

Zika Virus Neuropathogenesis: The Different Brain Cells, Host Factors and Mechanisms Involved

Zika virus (ZIKV), despite being discovered six decades earlier, became a major health concern only after an epidemic in French Polynesia and an increase in the number of microcephaly cases in Brazil. Substantial evidence has been found to support the link between ZIKV and neurological complications in infants. The virus targets various cells in the brain, including radial glial cells, neural progenitor cells (NPCs), astrocytes, microglial and glioblastoma stem cells. It affects the brain cells by exploiting different mechanisms, mainly through apoptosis and cell cycle dysregulation. The modulation of host immune response and the inflammatory process has also been demonstrated to play a critical role in ZIKV induced neurological complications. In addition to that, different ZIKV strains have exhibited specific neurotropism and unique molecular mechanisms. This review provides a comprehensive and up-to-date overview of ZIKV-induced neuroimmunopathogenesis by dissecting its main target cells in the brain, and the underlying cellular and molecular mechanisms. We highlighted the roles of the different ZIKV host factors and how they exploit specific host factors through various mechanisms. Overall, it covers key components for understanding the crosstalk between ZIKV and the brain.

OFD1: One gene, several disorders

The OFD1 protein is necessary for the formation of primary cilia and left–right asymmetry establishment but additional functions have also been ascribed to this multitask protein. When mutated, this protein results in a variety of phenotypes ranging from multiorgan involvement, such as OFD type I (OFDI) and Joubert syndromes (JBS10), and Primary ciliary dyskinesia (PCD), to the engagement of single tissues such as in the case of retinitis pigmentosa (RP23). The inheritance pattern of these condition differs from X‐linked dominant male‐lethal (OFDI) to X‐linked recessive (JBS10, PCD, and RP23). Distinctive biological peculiarities of the protein, which can contribute to explain the extreme clinical variability and the genetic mechanisms underlying the different disorders are discussed. The extensive spectrum of clinical manifestations observed in OFD1‐mutated patients represents a paradigmatic example of the complexity of genetic diseases. The elucidation of the mechanisms underlying this complexity will expand our comprehension of inherited disorders and will improve the clinical management of patients.

OFD Type I syndrome: lessons learned from a rare ciliopathy

The OFD1 gene was initially identified as the gene responsible for the X-linked dominant male lethal OFD type I syndrome, a developmental disorder ascribed to cilia disfunction. The transcript has been subsequently associated to four different X-linked recessive conditions, namely Joubert syndrome, retinitis pigmentosa, primary ciliary dyskinesia and Simpson-Golabi-Behmel type 2 syndrome. The centrosomal/basal body OFD1 protein has indeed been shown to be required for primary cilia formation and left-right asymmetry. The protein is also involved in other tasks, e.g. regulation of cellular protein content, constrain of the centriolar length, chromatin remodeling at DNA double strand breaks, control of protein quality balance and cell cycle progression, which might be mediated by non-ciliary activities. OFD1 represents a paradigmatic model of a protein that performs its diverse actions according to the cell needs and depending on the subcellular localization, the cell type/tissue and other possible factors still to be determined. An increased number of multitask protein, such as OFD1, may represent a partial explanation to human complexity, as compared with less complex organisms with an equal or slightly lower number of proteins.

The HOPS complex subunit VPS39 controls ciliogenesis through autophagy

Primary cilia are microtubule-based organelles that assemble and protrude from the surface of most mammalian cells during quiescence. The biomedical relevance of cilia is indicated by disorders ascribed to cilia dysfunction, known as ciliopathies, that display distinctive features including renal cystic disease. In this report, we demonstrate that vacuolar protein sorting 39 (VPS39), a component of the homotypic fusion and vacuole protein sorting (HOPS) complex, acts as a negative regulator of ciliogenesis in human renal cells, by controlling the localization of the intraflagellar transport 20 protein at the base of cilia through autophagy. Moreover, we show that VPS39 controls ciliogenesis through autophagy also in vivo in renal tubules of medaka fish. These observations suggest a direct involvement of the HOPS complex in the regulation of autophagy-mediated ciliogenesis and eventually in target selection. Interestingly, we show that the impact of autophagy modulation on ciliogenesis is cell-type dependent and strictly related to environmental stimuli. This report adds a further tile to the cilia-autophagy connection and suggests that VPS39 could represent a new biological target for the recovery of the cilia-related phenotypes observed in the kidneys of patients affected by ciliopathies.

A rare triad of morning glory disc anomaly, moyamoya vasculopathy, and transsphenoidal cephalocele: pathophysiological considerations and surgical management

Morning glory disc anomaly is a congenital abnormality of the optic disc and peripapillary retina reported as an isolated condition or associated with various anomalies, including basal encephaloceles and moyamoya vasculopathy. However, the co-occurrence of these three entities is extremely rare and the pathogenesis is still poorly understood. Moreover, data on the surgical management and long-term follow-up of the intracranial anomalies are scarce. Here, we describe the case of a 11-year-old boy with morning glory disc anomaly, transsphenoidal cephalocele, and moyamoya vasculopathy, who underwent bilateral indirect revascularization with encephalo-duro-myo-arterio-pericranio-synangiosis at the age of 2 years, and endoscopic repair of the transsphenoidal cephalocele at the age of 6 years. A rare missense variant (c.1081T>C,p.Tyr361His) was found in OFD1, a gene responsible for a X-linked ciliopathy, the oral-facial-digital syndrome type 1 (OFD1; OMIM 311200). This case expands the complex phenotype of OFD1 syndrome and suggests a possible involvement of OFD1 gene and Shh pathway in the pathogenesis of these anomalies.

Regulation of autophagosome biogenesis by OFD1-mediated selective autophagy

Autophagy is a lysosome-dependent degradation pathway essential to maintain cellular homeostasis. Therefore, either defective or excessive autophagy may be detrimental for cells and tissues. The past decade was characterized by significant advances in molecular dissection of stimulatory autophagy inputs; however, our understanding of the mechanisms that restrain autophagy is far from complete. Here, we describe a negative feedback mechanism that limits autophagosome biogenesis based on the selective autophagy-mediated degradation of ATG13, a component of the ULK1 autophagy initiation complex. We demonstrate that the centrosomal protein OFD1 acts as bona fide autophagy receptor for ATG13 via direct interaction with the Atg8/LC3/GABARAP family of proteins. We also show that patients with Oral-Facial-Digital type I syndrome, caused by mutations in the OFD1 gene, display excessive autophagy and that genetic inhibition of autophagy in a mouse model of the disease, significantly ameliorates polycystic kidney, a clinical manifestation of the disorder. Collectively, our data report the discovery of an autophagy self-regulated mechanism and implicate dysregulated autophagy in the pathogenesis of renal cystic disease in mammals.

Cilia, ciliopathies and hedgehog-related forebrain developmental disorders

Development of the forebrain critically depends on the Sonic Hedgehog (Shh) signaling pathway, as illustrated in humans by the frequent perturbation of this pathway in holoprosencephaly, a condition defined as a defect in the formation of midline structures of the forebrain and face. The Shh pathway requires functional primary cilia, microtubule-based organelles present on virtually every cell and acting as cellular antennae to receive and transduce diverse chemical, mechanical or light signals. The dysfunction of cilia in humans leads to inherited diseases called ciliopathies, which often affect many organs and show diverse manifestations including forebrain malformations for the most severe forms. The purpose of this review is to provide the reader with a framework to understand the developmental origin of the forebrain defects observed in severe ciliopathies with respect to perturbations of the Shh pathway. We propose that many of these defects can be interpreted as an imbalance in the ratio of activator to repressor forms of the Gli transcription factors, which are effectors of the Shh pathway. We also discuss the complexity of ciliopathies and their relationships with forebrain disorders such as holoprosencephaly or malformations of cortical development, and emphasize the need for a closer examination of forebrain defects in ciliopathies, not only through the lens of animal models but also taking advantage of the increasing potential of the research on human tissues and organoids.

Truncating mutations in exons 20 and 21 of OFD1 can cause primary ciliary dyskinesia without associated syndromic symptoms

BACKGROUND

Primary ciliary dyskinesia (PCD) is a motile ciliopathy, whose symptoms include airway infections, male infertility and situs inversus. Apart from the typical forms of PCD, rare syndromic PCD forms exist. Mutations of the X-linked OFD1 gene cause several syndromic ciliopathies, including oral-facial-digital syndrome type 1, Joubert syndrome type 10 (JBTS10), and Simpson-Golabi-Behmel syndrome type 2, the latter causing the X-linked syndromic form of PCD. Neurological and skeletal symptoms are characteristic for these syndromes, with their severity depending on the location of the mutation within the gene.

OBJECTIVES

To elucidate the role of motile cilia defects in the respiratory phenotype of PCD patients with C-terminal OFD1 mutations.

METHODS

Whole-exome sequencing in a group of 120 Polish PCD patients, mutation screening of the OFD1 coding sequence, analysis of motile cilia, and magnetic resonance brain imaging.

RESULTS

Four novel hemizygous OFD1 mutations, in exons 20 and 21, were found in men with a typical PCD presentation but without severe neurological, skeletal or renal symptoms characteristic for other OFD1-related syndromes. Magnetic resonance brain imaging in two patients did not show a molar tooth sign typical for JBTS10. Cilia in the respiratory epithelium were sparse, unusually long and displayed a defective motility pattern.

CONCLUSION

Consistent with the literature, truncations of the C-terminal part of OFD1 (exons 16-22) almost invariably cause a respiratory phenotype (due to motile cilia defects) while their impact on the primary cilia function is limited. We suggest that exons 20-21 should be included in the panel for regular mutation screening in PCD.

A novel pathogenic variant in OFD1 results in X-linked Joubert syndrome with orofaciodigital features and pituitary aplasia

Orofaciodigital syndrome type I and X-linked recessive Joubert syndrome are known ciliopathic disorders that are caused by pathogenic variants in OFD1 gene. Endocrine system involvement with these conditions is not well described. We present the first report of a newborn male with a novel hemizygous variant in OFD1 gene c.515T>C, (p.Leu172Pro) resulting in X-linked Joubert syndrome and orofaciodigital features with complete pituitary gland aplasia and subsequent severe hypoplasia of peripheral endocrine glands. This clinical report expands the phenotypic spectrum of endocrine system involvement in OFD1-related disorders and suggests that OFD1 gene may be related to pituitary gland development.

Long term exposure to cadmium: Pathological effects on kidney tubules cells in Sparus aurata juveniles

The effects of an exposure to cadmium chloride 0.47μM for 150days were studied in kidneys of juveniles Sparus aurata by a multidisciplinary approach so to correlate uptake and detoxification potential to changes in brush border and glycocalyx sugar composition. Results demonstrated that cadmium concentration in kidney significantly increased from day 30 reaching a plateau on day 120 while metallothioneins reached a peak on day 90 and by day 120 were already decreasing to control values. Cytological damage was extensive on day 90, clearly detectable at both structural and ultrastructural levels, in tubular cells and brush-border. Staining with a panel of four lectins revealed a significant increase in N-Ac-Gal and a decrease in mannose in the glycocalyx and the tubular basal membranes. From day 120, when cadmium concentration was high and metallothionein concentration decreasing, a clear recovery was observed in tubular cells morphology and sugar composition. Possible significance of these apparently contrasting data are discussed.

Micrognathia in mouse models of ciliopathies

Defects in the development of the mandible can lead to micrognathia, or small jaw, which manifests in ciliopathic conditions, such as orofaciodigital syndrome, Meckel-Gruber syndrome, and Bardet-Biedl syndrome. Although micrognathia occurs frequently in human and mouse ciliopathies, it has been difficult to pinpoint the underlying cellular causes. In this mini-review, we shed light on the tissue-specific contributions to ciliary dysfunction in the development of the mandible. First, we outline the steps involved in setting up the jaw primordium and subsequent steps in the outgrowth of the mandibular skeleton. We then determine the critical tissue interactions using mice carrying a conditional mutation in the cilia gene Ofd1 Our studies highlight the usefulness of the Ofd1 mouse model and illustrate long-term possibilities for understanding the cellular and biochemical events underlying micrognathia.

The centrosomal OFD1 protein interacts with the translation machinery and regulates the synthesis of specific targets

Protein synthesis is traditionally associated with specific cytoplasmic compartments. We now show that OFD1, a centrosomal/basal body protein, interacts with components of the Preinitiation complex of translation (PIC) and of the eukaryotic Initiation Factor (eIF)4F complex and modulates the translation of specific mRNA targets in the kidney. We demonstrate that OFD1 cooperates with the mRNA binding protein Bicc1 to functionally control the protein synthesis machinery at the centrosome where also the PIC and eIF4F components were shown to localize in mammalian cells. Interestingly, Ofd1 and Bicc1 are both involved in renal cystogenesis and selected targets were shown to accumulate in two models of inherited renal cystic disease. Our results suggest a possible role for the centrosome as a specialized station to modulate translation for specific functions of the nearby ciliary structures and may provide functional clues for the understanding of renal cystic disease.

Basal body positioning and anchoring in the multiciliated cell Paramecium tetraurelia: roles of OFD1 and VFL3

Background

The development of a ciliary axoneme requires the correct docking of the basal body at cytoplasmic vesicles or plasma membrane. In the multiciliated cell Paramecium, three conserved proteins, FOR20, Centrin 2, and Centrin 3 participate in this process, FOR20 and Centrin 2 being involved in the assembly of the transition zone. We investigated the function of two other evolutionary conserved proteins, OFD1 and VFL3, likely involved in this process.

Results

In Paramecium tetraurelia, a single gene encodes OFD1, while four genes encode four isoforms of VFL3, grouped into two families, VFL3-A and VFL3-B. Depletion of OFD1 and the sole VFL3-A family impairs basal body docking. Loss of OFD1 yields a defective assembly of the basal body distal part. Like FOR20, OFD1 is recruited early during basal body assembly and localizes at the transition zone between axoneme and membrane at the level of the microtubule doublets. While the recruitment of OFD1 and Centrin 2 proceed independently, the localizations of OFD1 and FOR20 at the basal body are interdependent. In contrast, in VFL3-A depleted cells, the unanchored basal bodies harbor a fully organized distal part but display an abnormal distribution of their associated rootlets which mark their rotational asymmetry. VFL3-A, which is required for the recruitment of Centrin 3, is transiently present near the basal bodies at an early step of their duplication. VFL3-A localizes at the junction between the striated rootlet and the basal body.

Conclusion

Our results demonstrate the conserved role of OFD1 in the anchoring mechanisms of motile cilia and establish its relations with FOR20 and Centrin 2. They support the hypothesis of its association with microtubule doublets. They suggest that the primary defect of VFL3 depletion is a loss of the rotational asymmetry of the basal body which specifies the sites of assembly of the appendages which guide the movement of basal bodies toward the cell surface. The localization of VFL3 outside of the basal body suggests that extrinsic factors could control this asymmetry.

Electronic supplementary material

The online version of this article (doi:10.1186/s13630-017-0050-z) contains supplementary material, which is available to authorized users.

Abnormal glycosylation in Joubert syndrome type 10

BACKGROUND

The discovery of disease pathogenesis requires systematic agnostic screening of multiple homeostatic processes that may become deregulated. We illustrate this principle in the evaluation and diagnosis of a 5-year-old boy with Joubert syndrome type 10 (JBTS10). He carried the OFD1 mutation p.Gln886Lysfs*2 (NM_003611.2: c.2656del) and manifested features of Joubert syndrome.

METHODS

We integrated exome sequencing, MALDI-TOF mass spectrometry analyses of plasma and cultured dermal fibroblasts glycomes, and full clinical evaluation of the proband. Analyses of cilia formation and lectin staining were performed by immunofluorescence. Measurement of cellular nucleotide sugar levels was performed with high-performance anion-exchange chromatography with pulsed amperometric detection. Statistical analyses utilized the Student's and Fisher's exact t tests.

RESULTS

Glycome analyses of plasma and cultured dermal fibroblasts identified abnormal N- and O-linked glycosylation profiles. These findings replicated in two unrelated males with OFD1 mutations. Cultured fibroblasts from affected individuals had a defect in ciliogenesis. The proband's fibroblasts also had an abnormally elevated nuclear sialylation signature and increased total cellular levels of CMP-sialic acid. Ciliogenesis and each glycosylation anomaly were rescued by expression of wild-type OFD1.

CONCLUSIONS

The rescue of ciliogenesis and glycosylation upon reintroduction of WT OFD1 suggests that both contribute to the pathogenesis of JBTS10.

Oral-facial-digital syndrome type I cells exhibit impaired DNA repair; unanticipated consequences of defective OFD1 outside of the cilia network

Defects in OFD1 underlie the clinically complex ciliopathy, Oral-Facial-Digital syndrome Type I (OFD Type I). Our understanding of the molecular, cellular and clinical consequences of impaired OFD1 originates from its characterised roles at the centrosome/basal body/cilia network. Nonetheless, the first described OFD1 interactors were components of the TIP60 histone acetyltransferase complex. We find that OFD1 can also localise to chromatin and its reduced expression is associated with mis-localization of TIP60 in patient-derived cell lines. TIP60 plays important roles in controlling DNA repair. OFD Type I cells exhibit reduced histone acetylation and altered chromatin dynamics in response to DNA double strand breaks (DSBs). Furthermore, reduced OFD1 impaired DSB repair via homologous recombination repair (HRR). OFD1 loss also adversely impacted upon the DSB-induced G2-M checkpoint, inducing a hypersensitive and prolonged arrest. Our findings show that OFD Type I patient cells have pronounced defects in the DSB-induced histone modification, chromatin remodelling and DSB-repair via HRR; effectively phenocopying loss of TIP60. These data extend our knowledge of the molecular and cellular consequences of impaired OFD1, demonstrating that loss of OFD1 can negatively impact upon important nuclear events; chromatin plasticity and DNA repair.

OFD1, as a Ciliary Protein, Exhibits Neuroprotective Function in Photoreceptor Degeneration Models

Ofd1 is a newly identified causative gene for Retinitis pigmentosa (RP), a photoreceptor degenerative disease. This study aimed to examine Ofd1 localization in retina and further to investigate its function in photoreceptor degeneration models. Ofd1 localization in rat retina was examined using immunofluorescence. N-methyl-N-nitrosourea (MNU)-induced rats and Royal College of Surgeons (RCS) rats were used as photoreceptor degeneration models. The expression pattern of Ofd1, other ciliary associated genes and Wnt signaling pathway genes were examined in rat models. Furthermore, pEGFP-Ofd1-CDS and pSUPER-Ofd1-shRNA were constructed to overexpress and knockdown the expression level in 661W and R28 cells. MNU was also used to induce cell death. Cilia formation was observed using immunocytochemistry (ICC). Reactive oxygen species (ROS) were detected using the 2', 7'-Dichlorofluorescin diacetate (DCFH-DA) assay. Apoptosis genes expression was examined using qRT-PCR, Western blotting and fluorescence-activated cell sorting (FACS). Ofd1 localized to outer segments of rat retina photoreceptors. Ofd1 and other ciliary proteins expression levels increased from the 1^st and 4^th postnatal weeks and decreased until the 6^th week in the RCS rats, while their expression consistently decreased from the 1^st and 7^th day in the MNU rats. Moreover, Wnt signaling pathway proteins expression was significantly up-regulated in both rat models. Knockdown of Ofd1 expression resulted in a smaller population, shorter length of cell cilia, and lower cell viability. Ofd1 overexpression partially attenuated MNU toxic effects by reducing ROS levels and mitigating apoptosis. To the best of our knowledge, this is the first study demonstrating Ofd1 localization and its function in rat retina and in retinal degeneration rat models. Ofd1 plays a role in controlling photoreceptor cilium length and number. Importantly, it demonstrates a neuroprotective function by protecting the photoreceptor from oxidative stress and apoptosis. These data have expanded our understanding of Ofd1 function beyond cilia, and we concluded that ofd1 neuroprotection could be a potential treatment strategy in retina degeneration models.

Update on oral-facial-digital syndromes (OFDS)

Oral-facial-digital syndromes (OFDS) represent a heterogeneous group of rare developmental disorders affecting the mouth, the face and the digits. Additional signs may involve brain, kidneys and other organs thus better defining the different clinical subtypes. With the exception of OFD types I and VIII, which are X-linked, the majority of OFDS is transmitted as an autosomal recessive syndrome. A number of genes have already found to be mutated in OFDS and most of the encoded proteins are predicted or proven to be involved in primary cilia/basal body function. Preliminary data indicate a physical interaction among some of those proteins and future studies will clarify whether all OFDS proteins are part of a network functionally connected to cilia. Mutations in some of the genes can also lead to other types of ciliopathies with partially overlapping phenotypes, such as Joubert syndrome (JS) and Meckel syndrome (MKS), supporting the concept that cilia-related diseases might be a continuous spectrum of the same phenotype with different degrees of severity. To date, seven of the described OFDS still await a molecular definition and two unclassified forms need further clinical and molecular validation. Next-generation sequencing (NGS) approaches are expected to shed light on how many OFDS geneticists should consider while evaluating oral-facial-digital cases. Functional studies will establish whether the non-ciliary functions of the transcripts mutated in OFDS might contribute to any of the phenotypic abnormalities observed in OFDS.

Small organelle, big responsibility: the role of centrosomes in development and disease

The centrosome, a key microtubule organizing centre, is composed of centrioles, embedded in a protein-rich matrix. Centrosomes control the internal spatial organization of somatic cells, and as such contribute to cell division, cell polarity and migration. Upon exiting the cell cycle, most cell types in the human body convert their centrioles into basal bodies, which drive the assembly of primary cilia, involved in sensing and signal transduction at the cell surface. Centrosomal genes are targeted by mutations in numerous human developmental disorders, ranging from diseases exclusively affecting brain development, through global growth failure syndromes to diverse pathologies associated with ciliary malfunction. Despite our much-improved understanding of centrosome function in cellular processes, we know remarkably little of its role in the organismal context, especially in mammals. In this review, we examine how centrosome dysfunction impacts on complex physiological processes and speculate on the challenges we face when applying knowledge generated from in vitro and in vivo model systems to human development.

CNS involvement in OFD1 syndrome: a clinical, molecular, and neuroimaging study

Background

Oral-facial-digital type 1 syndrome (OFD1; OMIM 311200) belongs to the expanding group of disorders ascribed to ciliary dysfunction. With the aim of contributing to the understanding of the role of primary cilia in the central nervous system (CNS), we performed a thorough characterization of CNS involvement observed in this disorder.

Methods

A cohort of 117 molecularly diagnosed OFD type I patients was screened for the presence of neurological symptoms and/or cognitive/behavioral abnormalities on the basis of the available information supplied by the collaborating clinicians. Seventy-one cases showing CNS involvement were further investigated through neuroimaging studies and neuropsychological testing.

Results

Seventeen patients were molecularly diagnosed in the course of this study and five of these represent new mutations never reported before. Among patients displaying neurological symptoms and/or cognitive/behavioral abnormalities, we identified brain structural anomalies in 88.7%, cognitive impairment in 68%, and associated neurological disorders and signs in 53% of cases. The most frequently observed brain structural anomalies included agenesis of the corpus callosum and neuronal migration/organisation disorders as well as intracerebral cysts, porencephaly and cerebellar malformations.

Conclusions

Our results support recent published findings indicating that CNS involvement in this condition is found in more than 60% of cases. Our findings correlate well with the kind of brain developmental anomalies described in other ciliopathies. Interestingly, we also described specific neuropsychological aspects such as reduced ability in processing verbal information, slow thought process, difficulties in attention and concentration, and notably, long-term memory deficits which may indicate a specific role of OFD1 and/or primary cilia in higher brain functions.

The role of primary cilia in the development and disease of the retina

The normal development and function of photoreceptors is essential for eye health and visual acuity in vertebrates. Mutations in genes encoding proteins involved in photoreceptor development and function are associated with a suite of inherited retinal dystrophies, often as part of complex multi-organ syndromic conditions. In this review, we focus on the role of the photoreceptor outer segment, a highly modified and specialized primary cilium, in retinal health and disease. We discuss the many defects in the structure and function of the photoreceptor primary cilium that can cause a class of inherited conditions known as ciliopathies, often characterized by retinal dystrophy and degeneration, and highlight the recent insights into disease mechanisms.