Phenotypic variability in 49 cases of ESCO2 mutations, including novel missense and codon deletion in the acetyltransferase domain, correlates with ESCO2 expression and establishes the clinical criteria for Roberts syndrome

Thalidomide-induced limb malformations: an update and reevaluation

Historically, thalidomide-induced congenital malformations have served as an important example of the enhanced susceptibility of developing embryos to chemical perturbation. The compound produced a wide variety of congenital malformations in humans, which were initially detected by an association with a relatively rare limb defect labeled phocomelia. Although true phocomelia in the most severe form is a transverse defect with intercalary absence of limb regions, it is proposed that thalidomide produces a longitudinal limb phenotype in humans under usual circumstances that can become transverse in severe cases with a preferential sensitivity of forelimb over hindlimb, preaxial over postaxial, and left more impacted than the corresponding non-autopod limb bones on the right. The thalidomide-induced limb phenotype in humans is described and followed by a hierarchical comparison with various laboratory animal species. Mechanistic studies have been hampered by the fact that only non-human primates and rabbits have malformations that are anatomically similar to humans. Included in this review are unpublished data on limb malformations produced by thalidomide in rhesus monkeys from experiments performed more than 50 years ago. The critical period in gestation for the induction of phocomelia may initiate prior to the development of the embryonic limb bud, which contrasts with other chemical and physical agents that are known to produce this phenotype. The importance of toxicokinetic parameters is reviewed including dose, enantiomers, absorption, distribution, and both non-enzymatic and enzymatic biotransformations. The limb embryopathy mechanism that provides a partial explanation of the limb phenotype is that cereblon binds to thalidomide creating a protein complex that ubiquitinates protein substrates (CRL4CRBN) that are not targets for the complex in the absence of the thalidomide. One of these neosubstrates is SALL4 which when mutated causes a syndrome that phenocopies aspects of thalidomide embryopathy. Other candidate neosubstrates for the complex that have been found in non-human species may contribute to an understanding of the limb defect including PLZF, p63, and various zinc finger transcription factors. It is proposed that it is important to consider the species-specificity of the compound when considering potential mechanistic pathways and that some of the more traditional mechanisms for explaining the embryopathy, such as anti-angiogenesis and redox perturbation, may contribute to a full understanding of this teratogen.

Limb reduction in an Esco2 cohesinopathy mouse model is mediated by p53-dependent apoptosis and vascular disruption

Roberts syndrome (RBS) is an autosomal recessive disorder with profound growth deficiency and limb reduction caused by ESCO2 loss-of-function variants. Here, we elucidate the pathogenesis of limb reduction in an Esco2fl/fl;Prrx1-CreTg/0 mouse model using bulk- and single-cell-RNA-seq and gene co-expression network analyses during embryogenesis. Our results reveal morphological and vascular defects culminating in hemorrhage of mutant limbs at E12.5. Underlying this abnormal developmental progression is a pre-apoptotic, mesenchymal cell population specific to mutant limb buds enriched for p53-related signaling beginning at E9.5. We then characterize these p53-related processes of cell cycle arrest, DNA damage, cell death, and the inflammatory leukotriene signaling pathway in vivo. In utero treatment with pifithrin-α, a p53 inhibitor, rescued the hemorrhage in mutant limbs. Lastly, significant enrichments were identified among genes associated with RBS, thalidomide embryopathy, and other genetic limb reduction disorders, suggesting a common vascular etiology among these conditions.

Case report: The evolving phenotype of ESCO2 spectrum disorder in a 15-year-old Malaysian child

ESCO2 spectrum disorder is an autosomal recessive developmental disorder characterized by growth retardation, symmetrical mesomelic limb malformation, and distinctive facies with microcephaly, with a wide phenotypic continuum that ranges from Roberts syndrome (MIM #268300) at the severe end to SC phocomelia (MIM #269000) at the milder end. ESCO2 encodes a 601-amino acid protein belonging to the Eco1/Ctf7 family of acetyltransferases that is involved in the establishment of sister chromatid cohesion, which is essential for accurate chromosome segregation and genomic stability and thus belongs to a group of disorders called "cohesinopathies". We describe a 15-year-old Malaysian female who presented with the characteristic triad of ESCO2 spectrum disorder, with an equivocal chromosomal breakage study and normal karyotyping findings. She was initially suspected to have mosaic Fanconi anemia but whole exome sequencing (WES) showed a likely pathogenic homozygous splice variant c.955 + 2_955+5del in the ESCO2 gene. During the 15-year diagnostic odyssey, she developed type 2 diabetes mellitus, primary ovarian insufficiency, increased optic cup-to-disc ratio with tortuous vessels bilaterally, and an evolving but distinct facial and skin hypopigmentation phenotype. Of note, there was an absence of learning disabilities. Our findings provide further evidence for ESCO2 spectrum disorder in an Asian child and contribute to defining the clinical and radiographic spectrum.

Cornelia de Lange Syndrome mutations in SMC1A cause cohesion defects in yeast

Cornelia de Lange Syndrome (CdLS) is a developmental disorder characterized by limb truncations, craniofacial abnormalities, and cognitive delays. CdLS is caused mainly by mutations in genes encoding subunits or regulators of the cohesin complex. Cohesin plays 2 distinct roles in chromosome dynamics as follows: it promotes looping, organization, and compaction of individual chromosomes, and it holds newly replicated sister chromatids together until cell division. CdLS-associated mutations result in altered gene expression likely by affecting chromosome architecture. Whether CdLS mutations cause phenotypes through impact on sister chromatid cohesion is less clear. Here, we show that CdLS-associated mutations introduced into the SMC1A gene of budding yeast had measurable impacts on sister chromatid cohesion, mitotic progression, and DNA damage sensitivity. These data suggest that sister chromatid cohesion-related defects may contribute to phenotypes seen in CdLS affected individuals.

Pseudo-Roberts Syndrome: An Entity or Not?

Background: Roberts syndrome is a genetic disorder characterized by tetra-phocomelia with abnormalities of ESCO2. We report a male stillborn with tetra-phocomelia and no ESCO2 mutation. Case report: Pre- and post-natal imaging and autopsy findings included schizencephaly, phocomelia of four limbs, micrognathia, oligodactyly, and cardiopulmonary malformations. Microcephaly on pre-natal imaging was not confirmed by autopsy examination. Karyotype, prenatal chromosome microarray and ESCO2 gene testing were normal. Conclusion: Given the various skeletal anomalies found on autopsy and imaging evaluations, at least phenotypically, our case appeared to conform into Roberts syndrome spectrum. Since the infant did not have the mutation associated with this disorder, this infant could be labeled as the first report of a pseudo-Roberts syndrome because many of his phenotypic anomalies are characteristic of Roberts syndrome in absence of the ESCO2 gene mutation.

Prenatal diagnosis of Roberts syndrome in a Chinese family based on ultrasound findings and whole exome sequencing: a case report

Background

Roberts syndrome (RBS) is a rare autosomal recessive disorder caused by variations in the ESCO2 gene; however, prenatal diagnosis of RBS has never been reported in Chinese families. Additionally, fetal-specific phenotypic characteristics associated with ESCO2 variants have not been reported.

Case presentation

A fetus in a healthy, nonconsanguineous Chinese family with multiple serious congenital malformations was diagnosed prenatally. Two consecutive fetuses in this family presented with tetraphocomelia, growth restriction, cleft lip and palate bilaterally, and other abnormalities. The main phenotypic characteristics of this case were strongly suspected to be associated with RBS. Finally, whole exome sequence analysis revealed the insertion of a homozygous base pair in exon 6 of the ESCO2 gene (NM_001017420.3, c.1111insA, NP_001017420.1, p.Thr371fs). Both of the couples were heterozygous carriers for this variant.

Conclusion

We are the first to report a prenatal case of RBS diagnosed in a Chinese family. Here, we have confirmed that the rare variant is a definite pathogenic variant, and we provide detailed phenotypic characteristics for the prenatal diagnosis of RBS due to this causative variant.

Juberg-Hayward syndrome is a cohesinopathy, caused by mutation in ESCO2

BACKGROUND

Juberg-Hayward syndrome (JHS; MIM 216100) is a rare autosomal recessive malformation syndrome, characterized by cleft lip/palate, microcephaly, ptosis, short stature, hypoplasia or aplasia of thumbs, and dislocation of radial head and fusion of humerus and radius leading to elbow restriction.

OBJECTIVE

To report for the first time the molecular aetiology of JHS.

PATIENT AND METHODS

Clinical and radiographic examination, whole exome sequencing, Sanger sequencing, mutant protein model construction, and in situ hybridization of Esco2 expression in mouse embryos were performed.

RESULTS

Clinical findings of the patient consisted of repaired cleft lip/palate, microcephaly, ptosis, short stature, delayed bone age, hypoplastic fingers and thumbs, clinodactyly of the fifth fingers, and humeroradial synostosis leading to elbow restriction. Intelligence is normal. Whole exome sequencing of the whole family showed a novel homozygous base substitution c.1654C>T in ESCO2 of the proband. The sister was homozygous for the wildtype variant. Parents were heterozygous for the mutation. The mutation is predicted to cause premature stop codon p.Arg552Ter. Mutations in ESCO2, a gene involved in cohesin complex formation, are known to cause Roberts/SC phocomelia syndrome. Roberts/SC phocomelia syndrome and JHS share similar clinical findings, including autosomal recessive inheritance, short stature, cleft lip/palate, severe upper limb anomalies, and hypoplastic digits. Esco2 expression during the early development of lip, palate, eyelid, digits, upper limb, and lower limb and truncated protein model are consistent with the defect.

CONCLUSIONS

Our study showed that Roberts/SC phocomelia syndrome and JHS are allelic and distinct entities. This is the first report demonstrating that mutation in ESCO2 causes JHS, a cohesinopathy.

5q35 duplication presents with psychiatric and undergrowth phenotypes mediated by NSD1 overexpression and mTOR signaling downregulation

PURPOSE

Nuclear receptor binding SET domain protein 1, NSD1, encodes a histone methyltransferase H3K36. NSD1 is responsible for the phenotype of the reciprocal 5q35.2q35.3 microdeletion-microduplication syndromes. We expand the phenotype and demonstrate the functional role of NSD1 in microduplication 5q35 syndrome.

METHODS

Through an international collaboration, we report nine new patients, contributing to the emerging phenotype, highlighting psychiatric phenotypes in older affected individuals. Focusing specifically on the undergrowth phenotype, we have modeled the effects of Mes-4/NSD overexpression in Drosophila melanogaster.

RESULTS

The individuals (including a family) from diverse backgrounds with duplications ranging in size from 0.6 to 4.5 Mb, have a consistent undergrowth phenotype. Mes-4 overexpression in the developing wing causes undergrowth, increased H3K36 methylation, and increased apoptosis. We demonstrate that altering the levels of insulin receptor (IR) rescues the apoptosis and the wing undergrowth phenotype, suggesting changes in mTOR pathway signaling. Leucine supplementation rescued Mes-4/NSD induced cell death, demonstrating decreased mTOR signaling caused by NSD1.

CONCLUSION

Given that we show mTOR inhibition as a likely mechanism and amelioration of the phenotype by leucine supplementation in a fly model, we suggest further studies should evaluate the therapeutic potential of leucine or branched chain amino acids as an adjunct possible treatment to ameliorate human growth and psychiatric phenotypes and propose inclusion of 5q35-microduplication as part of the differential diagnosis for children and adults with delayed bone age, short stature, microcephaly, developmental delay, and psychiatric phenotypes.

Genetics and signaling mechanisms of orofacial clefts

Craniofacial development involves several complex tissue movements including several fusion processes to form the frontonasal and maxillary structures, including the upper lip and palate. Each of these movements are controlled by many different factors that are tightly regulated by several integral morphogenetic signaling pathways. Subject to both genetic and environmental influences, interruption at nearly any stage can disrupt lip, nasal, or palate fusion and result in a cleft. Here, we discuss many of the genetic risk factors that may contribute to the presentation of orofacial clefts in patients, and several of the key signaling pathways and underlying cellular mechanisms that control lip and palate formation, as identified primarily through investigating equivalent processes in animal models, are examined.

Juberg-Hayward syndrome and Roberts syndrome are allelic, caused by mutations in ESCO2

OBJECTIVE

Juberg-Hayward syndrome (JHS; MIM 216100) is a rare autosomal recessive malformation syndrome, characterized by cleft lip/palate, microcephaly, ptosis, hypoplasia or aplasia of thumbs, short stature, dislocation of radial head, and fusion of humerus and radius leading to elbow restriction. A homozygous mutation in ESCO2 has recently been reported to cause Juberg-Hayward syndrome. Our objective was to investigate the molecular etiology of Juberg-Hayward syndrome in two affected Lisu tribe brothers.

MATERIALS AND METHODS

Two patients, the unaffected parents, and two unaffected siblings were studied. Clinical and radiographic examination, whole exome sequencing, Sanger sequencing, Western blot analysis, and chromosome testing were performed.

RESULTS

Two affected brothers had characteristic features of Juberg-Hayward syndrome, except for the absence of microcephaly. The elder brother had bilateral cleft lip and palate, short stature, humeroradial synostosis, and simple partial seizure with secondary generalization. The younger brother had unilateral cleft lip and palate, short stature, and dislocation of radial heads. The homozygous (c.1654C > T; p.Arg552Ter) mutation in ESCO2 was identified in both patients. The other unaffected members of the family were heterozygous for the mutation. The presence of humeroradial synostosis and radial head dislocation in the same family is consistent with both being in the same spectrum of forearm malformations. Chromosome testing of the affected patients showed premature centromere separation. Western blot analysis showed reduced amount of truncated protein.

CONCLUSION

Our findings confirm that a homozygous mutation in ESCO2 is the underlying cause of Juberg-Hayward syndrome. Microcephaly does not appear to be a consistent feature of the syndrome.

Roberts syndrome in an Indian patient with humeroradial synostosis, congenital elbow contractures and a novel homozygous splice variant in ESCO2

Roberts syndrome (also known as Roberts-SC phocomelia syndrome) is an autosomal recessive developmental disorder, characterized by pre- and postnatal growth retardation, limb malformations including bilateral symmetric tetraphocomelia or mesomelia, and craniofacial dysmorphism. Biallelic loss-of-function variants in ESCO2, which codes for establishment of sister chromatid cohesion N-acetyltransferase 2, cause Roberts syndrome. Phenotypic spectrum among patients is broad, challenging clinical diagnosis in mildly affected individuals. Here we report a 3-year-old boy with a mild phenotype of Roberts syndrome with bilateral elbow contractures, humeroradial synostosis, mild lower limb disparity, and facial dysmorphism. Trio whole-exome sequencing identified the novel biallelic splice variant c.1673+1G>A in ESCO2 in the patient. Aberrant ESCO2 pre-mRNA splicing, reduced relative ESCO2 mRNA amount, and characteristic cytogenetic defects, such as premature centromere separation, heterochromatin repulsion, and chromosome breaks, in patient cells strongly supported pathogenicity of the ESCO2 variant affecting one of the highly conserved guanine-thymine dinucleotide of the donor splice site. Our case highlights the difficulty in establishing a clinical diagnosis in individuals with minor clinical features of Roberts syndrome and normal intellectual and social development. However, next-generation sequencing tools allow for molecular diagnosis in cases presenting with mild developmental defects.

Non-redundant roles in sister chromatid cohesion of the DNA helicase DDX11 and the SMC3 acetyl transferases ESCO1 and ESCO2

In a process linked to DNA replication, duplicated chromosomes are entrapped in large, circular cohesin complexes and functional sister chromatid cohesion (SCC) is established by acetylation of the SMC3 cohesin subunit. Roberts Syndrome (RBS) and Warsaw Breakage Syndrome (WABS) are rare human developmental syndromes that are characterized by defective SCC. RBS is caused by mutations in the SMC3 acetyltransferase ESCO2, whereas mutations in the DNA helicase DDX11 lead to WABS. We found that WABS-derived cells predominantly rely on ESCO2, not ESCO1, for residual SCC, growth and survival. Reciprocally, RBS-derived cells depend on DDX11 to maintain low levels of SCC. Synthetic lethality between DDX11 and ESCO2 correlated with a prolonged delay in mitosis, and was rescued by knockdown of the cohesin remover WAPL. Rescue experiments using human or mouse cDNAs revealed that DDX11, ESCO1 and ESCO2 act on different but related aspects of SCC establishment. Furthermore, a DNA binding DDX11 mutant failed to correct SCC in WABS cells and DDX11 deficiency reduced replication fork speed. We propose that DDX11, ESCO1 and ESCO2 control different fractions of cohesin that are spatially and mechanistically separated.

Report of the Phenotype of a Patient with Roberts Syndrome and a Rare ESCO2 Variant

Roberts syndrome is a rare autosomal recessive genetic disease. In this report, we report a Brazilian patient with a rare ESCO2 variant. The patient manifested a broad range of clinical findings including the significant, bilateral shortening of the extremities. He deteriorated and passed away at 20 days of age. High-resolution GTG-banded karyotype showed lack of centromeric constriction in some chromosomes, premature centromere separation in others, and repulsion of the heterochromatin regions. Molecular analysis of the ESCO2 gene revealed a deletion of 4 bp involving exon 4 in homozygosity (NM_00107420.2:c.875_878delACAG), which causes loss of ESCO2 function. We describe the clinical presentation caused by a rare ESCO2 variant.

The many lives of KATs - detectors, integrators and modulators of the cellular environment

Research over the past three decades has firmly established lysine acetyltransferases (KATs) as central players in regulating transcription. Recent advances in genomic sequencing, metabolomics, animal models and mass spectrometry technologies have uncovered unexpected new roles for KATs at the nexus between the environment and transcriptional regulation. Thousands of reversible acetylation sites have been mapped in the proteome that respond dynamically to the cellular milieu and maintain major processes such as metabolism, autophagy and stress response. Concurrently, researchers are continuously uncovering how deregulation of KAT activity drives disease, including cancer and developmental syndromes characterized by severe intellectual disability. These novel findings are reshaping our view of KATs away from mere modulators of chromatin to detectors of the cellular environment and integrators of diverse signalling pathways with the ability to modify cellular phenotype.

Enhancers: bridging the gap between gene control and human disease

Enhancers are a class of regulatory elements essential for precise spatio-temporal control of gene expression during development and in terminally differentiated cells. This review highlights signature features of enhancer elements as well as new advances that provide mechanistic insights into enhancer-mediated gene control in the context of three-dimensional chromatin. We detail the various ways in which non-coding mutations can instigate aberrant gene control and cause a variety of Mendelian disorders, common diseases and cancer.

A sclerocornea-associated RAD21 variant induces corneal stroma disorganization

Sclerocornea is a cornea opacification disorder. Disorganized corneal stroma fibrils are observed in patients' cornea. Previously we identified a RAD21^C1348T variant that is associated with a peripheral sclerocornea pedigree. To explore whether this RAD21 variant can induce sclerocornea-related phenotype, and to investigate the possible mechanisms of such phenotype, the orthologous rad21 wild-type and variant mRNAs were injected into Xenopus laevis embryos and the developed eyes were subjected for histological examination. Transmission electron microscopy was applied for corneal stroma organization check. rad21 is highly expressed in the eye region during X. laevis development. Disrupted eye development was observed in the rad21 variant injected embryos. Disorganized corneal stroma and decreased diameters of collagen fibrils were observed in the rad21 variant injected X. laevis eyes. These eye defects can be rescued by overexpression of the wild-type rad21. Histological examination found stroma attracting center, a key structure in X. laevis corneal development, was impaired in rad21 variant injected embryos. Our results suggest a key role of RAD21 during corneal development. Our data indicates the RAD21^R450C variant contributes to peripheral sclerocornea by disturbing collagen fibril organization in the corneal stroma.

Roles of cohesin in chromosome architecture and gene expression

Cohesin-mediated chromatin organization plays an important role in formation and stabilization of chromosome architecture and gene regulation. Mechanisms by which cohesin shapes chromosome and regulates gene expression remain unclear. The present article overviews biological characters and functions of cohesin and core subunits and explores roles of regulatory factors (e.g. Pds5, Wapl, and Eco1) in dynamic behaviors of cohesin. Cohesin interacts with CCCTC binding factor (CTCF) and other factors to maintain and stabilize multi-dimensional organizations of topological loops and distances between sites during cell segmentation. We also describe functional roles of cohesin in cell cycle by entrapping sister chromatids to form embrace and handcuff models, loading onto chromatin, establishing cohesion function, and regulating removal of cohesin and associated factors from the chromosome arm through prophase pathway or at onset of anaphase. It is questioned whether those factors associated with cohesin-regulated processes can be identified as biology- or disease-specific biomarkers and druggable targets to dynamically monitor changes during phasing, staging, progressing, and responding of diseases. It is also expected to explore heterogenetic roles of cohesin between single cells and regulatory roles of cohesin in trans-omic profiles and functions. Further understanding of cohesin functions will be beneficial to improve diagnosis and treatment of cohesinopathies.

A Roberts Syndrome Individual With Differential Genotoxin Sensitivity and a DNA Damage Response Defect

PURPOSE

Roberts syndrome (RBS) is a rare, recessively transmitted developmental disorder characterized by growth retardation, craniofacial abnormalities, and truncation of limbs. All affected individuals to date have mutations in the ESCO2 (establishment of cohesion 2) gene, a key regulator of the cohesin complex, which is involved in sister chromatid cohesion and DNA double-strand break (DSB) repair. Here we characterize DNA damage responses (DDRs) for the first time in an RBS-affected family.

METHODS AND MATERIALS

Lymphoblastoid cell lines were established from an RBS family, including the proband and parents carrying ESCO2 mutations. Various DDR assays were performed on these cells, including cell survival, chromosome break, and apoptosis assays; checkpoint activation indicators; and measures of DNA breakage and repair.

RESULTS

Cells derived from the RBS-affected individual showed sensitivity to ionizing radiation (IR) and mitomycin C-induced DNA damage. In this ESCO2 compound heterozygote, other DDRs were also defective, including enhanced IR-induced clastogenicity and apoptosis; increased DNA DSB induction; and a reduced capacity for repairing IR-induced DNA DSBs, as measured by γ-H2AX foci and the comet assay.

CONCLUSIONS

In addition to its developmental features, RBS can be, like ataxia telangiectasia, considered a DDR-defective syndrome, which contributes to its cellular, molecular, and clinical phenotype.

Cul4-Ddb1 ubiquitin ligases facilitate DNA replication-coupled sister chromatid cohesion through regulation of cohesin acetyltransferase Esco2

Cohesin acetyltransferases ESCO1 and ESCO2 play a vital role in establishing sister chromatid cohesion. How ESCO1 and ESCO2 are controlled in a DNA replication-coupled manner remains unclear in higher eukaryotes. Here we show a critical role of CUL4-RING ligases (CRL4s) in cohesion establishment via regulating ESCO2 in human cells. Depletion of CUL4A, CUL4B or DDB1 subunits substantially reduces the normal cohesion efficiency. We also show that MMS22L, a vertebrate ortholog of yeast Mms22, is one of DDB1 and CUL4-associated factors (DCAFs) involved in cohesion. Several lines of evidence show selective interaction of CRL4s with ESCO2 through LxG motif, which is lost in ESCO1. Depletion of either CRL4s or ESCO2 causes a defect in SMC3 acetylation, which can be rescued by HDAC8 inhibition. More importantly, both CRL4s and PCNA act as mediators for efficiently stabilizing ESCO2 on chromatin and catalyzing SMC3 acetylation. Taken together, we propose an evolutionarily conserved mechanism in which CRL4s and PCNA promote ESCO2-dependent establishment of sister chromatid cohesion.

Phenotypic Overlap of Roberts and Baller-Gerold Syndromes in Two Patients With Craniosynostosis, Limb Reductions, and ESCO2 Mutations

Baller-Gerold (BGS, MIM#218600) and Roberts (RBS, MIM#268300) syndromes are rare autosomal recessive disorders caused, respectively, by biallelic alterations in RECQL4 (MIM^*603780) and ESCO2 (MIM^*609353) genes. Common features are severe growth retardation, limbs shortening and craniofacial abnormalities which may include craniosynostosis. We aimed at unveiling the genetic lesions underpinning the phenotype of two unrelated children with a presumptive BGS diagnosis: patient 1 is a Turkish girl with short stature, microcephaly, craniosynostosis, seizures, intellectual disability, midface hemangioma, bilateral radial and thumb aplasia, tibial hypoplasia, and pes equinovarus. Patient 2 is an Iranian girl born to consanguineous parents with craniosynostosis, micrognathism, bilateral radial aplasia, thumbs, and foot deformity in the context of developmental delay. Upon negative RECQL4 test, whole exome sequencing (WES) analysis performed on the two trios led to the identification of two different ESCO2 homozygous inactivating variants: a previously described c.1131+1G>A transition in patient 1 and an unreported deletion, c.417del, in patient 2, thus turning the diagnosis into Roberts syndrome. The occurrence of a Baller-Gerold phenotype in two unrelated patients that were ultimately diagnosed with RBS demonstrates the strength of WES in redefining the nosological landscape of rare congenital malformation syndromes, a premise to yield optimized patients management and family counseling.

Holt-Oram syndrome: clinical and molecular description of 78 patients with TBX5 variants

Holt-Oram syndrome (HOS) is an autosomal dominant condition characterised by the association of congenital heart defect (CHD), with or without rhythm disturbances and radial defects, due to TBX5 variants. The diagnosis is challenged by the variability of expression and the large phenotypic overlap with other conditions, like Okihiro syndrome, TAR syndrome or Fanconi disease. We retrospectively reviewed 212 patients referred for suspicion of HOS between 2002 and 2014, who underwent TBX5 screening. A TBX5 variant has been identified in 78 patients, representing the largest molecular series ever described. In the cohort, 61 met the previously described diagnostic criteria and 17 have been considered with an uncertain HOS diagnosis. A CHD was present in 91% of the patients with a TBX5 variant, atrial septal defects being the most common (61.5%). The genotype-phenotype study highlights the importance of some critical features in HOS: the septal characteristic of the CHD, the bilateral and asymmetric characteristics of the radial defect and the presence of shoulder or elbow mobility defect. Besides, 21 patients presented with an overlapping condition. Among them, 13 had a typical HOS presentation. We discuss the strategies that could be adopted to improve the molecular delineation of the remaining typical patients.

Long-term survival after corrective surgeries in two patients with severe deformities due to Roberts syndrome: A Case report and review of the literature

Roberts syndrome (RBS; OMIM 268300) is a rare autosomal recessive disease characterized by retardation before and after birth, cranial and maxillofacial deformities, limb anomalies and intellectual disability. Mutations in the establishment of cohesion 1 homologue 2 (ESCO2) gene on chromosome 8p21.1 have been found to be causative for RBS. We describe two patients with RBS with physical deformities and ll. One is an 8-year-old Yemeni male, and the other is his 13-year-old sister. These patients were diagnosed with RBS and underwent surgeries during their first to third years of life. Here, we present the cases for the two patients, focusing specifically on their surgical management and outcomes. Additionally, by reviewing the literature on RBS, we also summarize the proper surgical interventions for this rare disease. This paper describes the long-term follow-up of two patients with severe deformities who benefitted from corrective surgeries. The findings of this study indicate that patients who survive infancy and reach adulthood, even patients who present with severe disease symptoms, can benefit from corrective surgeries and lead better lives.

Expanding the mutation and clinical spectrum of Roberts syndrome

Roberts syndrome and SC phocomelia syndrome are rare autosomal recessive genetic disorders representing the extremes of the spectrum of severity of the same condition, caused by mutations in ESCO2 gene. We report three new patients with Roberts syndrome from three unrelated consanguineous Egyptian families. All patients presented with growth retardation, mesomelic shortening of the limbs more in the upper than in the lower limbs and microcephaly. Patients were subjected to clinical, cytogenetic and radiologic examinations. Cytogenetic analysis showed the characteristic premature separation of centromeres and puffing of heterochromatic regions. Further, sequencing of the ESCO2 gene identified a novel mutation c.244_245dupCT (p.T83Pfs*20) in one family besides two previously reported mutations c.760_761insA (p.T254Nfs*27) and c.764_765delTT (p.F255Cfs*25). All mutations were in homozygous state, in exon 3. The severity of the mesomelic shortening of the limbs and craniofacial anomalies showed variability among patients. Interestingly, patient 1 had abnormal skin hypopigmentation. Serial fetal ultrasound examinations and measurements of long bones diagnosed two affected fetuses in two of the studied families. A literature review and case comparison was performed. In conclusion, we report a novel ESCO2 mutation and expand the clinical spectrum of Roberts syndrome.

Genome stability: What we have learned from cohesinopathies

Cohesin is a multiprotein complex involved in many DNA-related processes such as proper chromosome segregation, replication, transcription, and repair. Mutations in cohesin gene pathways are responsible for human diseases, collectively referred to as cohesinopathies. In addition, both cohesin gene expression dysregulation and mutations have been identified in cancer. Cohesinopathy cells are characterized by genome instability (GIN) visualized by a constellation of markers such as chromosome aneuploidies, chromosome aberrations, precocious sister chromatid separation, premature centromere separation, micronuclei formation, and sensitivity to genotoxic drugs. The emerging picture suggests that GIN observed in cohesinopathies may result from the synergistic effects of the multiple cohesin dysfunctions. © 2016 Wiley Periodicals, Inc.

Sister Chromatid Cohesion Establishment Factor ESCO1 Operates by Substrate-Assisted Catalysis

Sister chromatid cohesion, formed by the cohesin protein complex, is essential for chromosome segregation. In order for cohesion to be established, the cohesin subunit SMC3 needs to be acetylated by a homolog of the ESCO1/Eco1 acetyltransferases, the enzymatic mechanism of which has remained unknown. Here we report the crystal structure of the ESCO1 acetyltransferase domain in complex with acetyl-coenzyme A, and show by SAXS that ESCO1 is a dimer in solution. The structure reveals an active site that lacks a potential catalytic base side chain. However, mutation of glutamate 789, a surface residue that is close to the automodification target lysine 803, strongly reduces autoacetylation of ESCO1. Moreover, budding yeast Smc3 mutated at the conserved residue D114, adjacent to the cohesion-activating acetylation site K112,K113, cannot be acetylated in vivo. This indicates that ESCO1 controls cohesion through substrate-assisted catalysis. Thus, this study discloses a key mechanism for cohesion establishment.

Variations in dysfunction of sister chromatid cohesion in esco2 mutant zebrafish reflect the phenotypic diversity of Roberts syndrome

Mutations in ESCO2, one of two establishment of cohesion factors necessary for proper sister chromatid cohesion (SCC), cause a spectrum of developmental defects in the autosomal-recessive disorder Roberts syndrome (RBS), warranting in vivo analysis of the consequence of cohesion dysfunction. Through a genetic screen in zebrafish targeting embryonic-lethal mutants that have increased genomic instability, we have identified an esco2 mutant zebrafish. Utilizing the natural transparency of zebrafish embryos, we have developed a novel technique to observe chromosome dynamics within a single cell during mitosis in a live vertebrate embryo. Within esco2 mutant embryos, we observed premature chromatid separation, a unique chromosome scattering, prolonged mitotic delay, and genomic instability in the form of anaphase bridges and micronuclei formation. Cytogenetic studies indicated complete chromatid separation and high levels of aneuploidy within mutant embryos. Amongst aneuploid spreads, we predominantly observed decreases in chromosome number, suggesting that either cells with micronuclei or micronuclei themselves are eliminated. We also demonstrated that the genomic instability leads to p53-dependent neural tube apoptosis. Surprisingly, although many cells required Esco2 to establish cohesion, 10-20% of cells had only weakened cohesion in the absence of Esco2, suggesting that compensatory cohesion mechanisms exist in these cells that undergo a normal mitotic division. These studies provide a unique in vivo vertebrate view of the mitotic defects and consequences of cohesion establishment loss, and they provide a compensation-based model to explain the RBS phenotypes.

Overexpression of a truncated CTF7 construct leads to pleiotropic defects in reproduction and vegetative growth in Arabidopsis

BACKGROUND

Eco1/Ctf7 is essential for the establishment of sister chromatid cohesion during S phase of the cell cycle. Inactivation of Ctf7/Eco1 leads to a lethal phenotype in most organisms. Altering Eco1/Ctf7 levels or point mutations in the gene can lead to alterations in nuclear division as well as a wide range of developmental defects. Inactivation of Arabidopsis CTF7 (AtCTF7) results in severe defects in reproduction and vegetative growth.

RESULTS

To further investigate the function(s) of AtCTF7, a tagged version of AtCTF7 and several AtCTF7 deletion constructs were created and transformed into wild type or ctf7 +/- plants. Transgenic plants expressing 35S:NTAP:AtCTF7∆299-345 (AtCTF7∆B) displayed a wide range of phenotypic alterations in reproduction and vegetative growth. Male meiocytes exhibited chromosome fragmentation and uneven chromosome segregation. Mutant ovules contained abnormal megasporocyte-like cells during pre-meiosis, megaspores experienced elongated meiosis and megagametogenesis, and defective megaspores/embryo sacs were produced at various stages. The transgenic plants also exhibited a broad range of vegetative defects, including meristem disruption and dwarfism that were inherited in a non-Mendelian fashion. Transcripts for epigenetically regulated transposable elements (TEs) were elevated in transgenic plants. Transgenic plants expressing 35S:AtCTF7∆B displayed similar vegetative defects, suggesting the defects in 35S:NTAP:AtCTF7∆B plants are caused by high-level expression of AtCTF7∆B.

CONCLUSIONS

High level expression of AtCTF7∆B disrupts megasporogenesis, megagametogenesis and male meiosis, as well as causing a broad range of vegetative defects, including dwarfism that are inherited in a non-Mendelian fashion.

3D-FISH analysis reveals chromatid cohesion defect during interphase in Roberts syndrome

Background

Roberts syndrome (RBS) is a rare autosomal recessive disorder mainly characterized by growth retardation, limb defects and craniofacial anomalies. Characteristic cytogenetic findings are “railroad track” appearance of chromatids and premature centromere separation in metaphase spreads. Mutations in the ESCO2 (establishment of cohesion 1 homolog 2) gene located in 8p21.1 have been found in several families. ESCO2, a member of the cohesion establishing complex, has a role in the effective cohesion between sister chromatids. In order to analyze sister chromatids topography during interphase, we performed 3D-FISH using pericentromeric heterochromatin probes of chromosomes 1, 4, 9 and 16, on preserved nuclei from a fetus with RBS carrying compound heterozygous null mutations in the ESCO2 gene.

Results

Along with the first observation of an abnormal separation between sister chromatids in heterochromatic regions, we observed a statistically significant change in the intranuclear localization of pericentromeric heterochromatin of chromosome 1 in cells of the fetus compared to normal cells, demonstrating for the first time a modification in the spatial arrangement of chromosome domains during interphase.

Conclusion

We hypothesize that the disorganization of nuclear architecture may result in multiple gene deregulations, either through disruption of DNA cis interaction –such as modification of chromatin loop formation and gene insulation - mediated by cohesin complex, or by relocation of chromosome territories. These changes may modify interactions between the chromatin and the proteins associated with the inner nuclear membrane or the pore complexes. This model offers a link between the molecular defect in cohesion and the complex phenotypic anomalies observed in RBS.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-014-0059-6) contains supplementary material, which is available to authorized users.

The roles of cohesins in mitosis, meiosis, and human health and disease

Mitosis and meiosis are essential processes that occur during development. Throughout these processes, cohesion is required to keep the sister chromatids together until their separation at anaphase. Cohesion is created by multiprotein subunit complexes called cohesins. Although the subunits differ slightly in mitosis and meiosis, the canonical cohesin complex is composed of four subunits that are quite diverse. The cohesin complexes are also important for DNA repair, gene expression, development, and genome integrity. Here we provide an overview of the roles of cohesins during these different events as well as their roles in human health and disease, including the cohesinopathies. Although the exact roles and mechanisms of these proteins are still being elucidated, this review serves as a guide for the current knowledge of cohesins.

Diverse developmental disorders from the one ring: distinct molecular pathways underlie the cohesinopathies

The multi-subunit protein complex, cohesin, is responsible for sister chromatid cohesion during cell division. The interaction of cohesin with DNA is controlled by a number of additional regulatory proteins. Mutations in cohesin, or its regulators, cause a spectrum of human developmental syndromes known as the “cohesinopathies.” Cohesinopathy disorders include Cornelia de Lange Syndrome and Roberts Syndrome. The discovery of novel roles for chromatid cohesion proteins in regulating gene expression led to the idea that cohesinopathies are caused by dysregulation of multiple genes downstream of mutations in cohesion proteins. Consistent with this idea, Drosophila, mouse, and zebrafish cohesinopathy models all show altered expression of developmental genes. However, there appears to be incomplete overlap among dysregulated genes downstream of mutations in different components of the cohesion apparatus. This is surprising because mutations in all cohesion proteins would be predicted to affect cohesin’s roles in cell division and gene expression in similar ways. Here we review the differences and similarities between genetic pathways downstream of components of the cohesion apparatus, and discuss how such differences might arise, and contribute to the spectrum of cohesinopathy disorders. We propose that mutations in different elements of the cohesion apparatus have distinct developmental outcomes that can be explained by sometimes subtly different molecular effects.

Cohesins repress Kaposi's sarcoma-associated herpesvirus immediate early gene transcription during latency

Chromatin-organizing factors such as CTCF and cohesins have been implicated in the control of complex viral regulatory programs. We investigated the role of CTCF and cohesins in the control of the switch from latency to the lytic cycle for Kaposi's sarcoma-associated herpesvirus (KSHV). We found that cohesin subunits but not CTCF are required for the repression of KSHV immediate early gene transcription. Depletion of the cohesin subunits Rad21, SMC1, and SMC3 resulted in lytic cycle gene transcription and viral DNA replication. In contrast, depletion of CTCF failed to induce lytic transcription or DNA replication. Chromatin immunoprecipitation with high-throughput sequencing (ChIP-Seq) revealed that cohesins and CTCF bound to several sites within the immediate early control region for ORF50 and to more distal 5' sites that also regulate the divergently transcribed ORF45-ORF46-ORF47 gene cluster. Rad21 depletion led to a robust increase in ORF45, ORF46, ORF47, and ORF50 transcripts, with similar kinetics to that observed with chemical induction by sodium butyrate. During latency, the chromatin between the ORF45 and ORF50 transcription start sites was enriched in histone H3K4me3, with elevated H3K9ac at the ORF45 promoter and elevated H3K27me3 at the ORF50 promoter. A paused form of RNA polymerase II (Pol II) was loosely associated with the ORF45 promoter region during latency but was converted to an active elongating form upon reactivation induced by Rad21 depletion. Butyrate treatment caused a rapid dissociation of cohesins and loss of CTCF binding at the immediate early gene locus, suggesting that cohesins may be a direct target of butyrate-mediated lytic induction. Our findings implicate cohesins as a major repressor of KSHV lytic gene activation and show that they function coordinately with CTCF to regulate the switch between latent and lytic gene activity.

Cohesin acetyltransferase Esco2 is a cell viability factor and is required for cohesion in pericentric heterochromatin

Sister chromatid cohesion, mediated by cohesin and regulated by Sororin, is essential for chromosome segregation. In mammalian cells, cohesion establishment and Sororin recruitment to chromatin-bound cohesin depends on the acetyltransferases Esco1 and Esco2. Mutations in Esco2 cause Roberts syndrome, a developmental disease in which mitotic chromosomes have a 'railroad' track morphology. Here, we show that Esco2 deficiency leads to termination of mouse development at pre- and post-implantation stages, indicating that Esco2 functions non-redundantly with Esco1. Esco2 is transiently expressed during S-phase when it localizes to pericentric heterochromatin (PCH). In interphase, Esco2 depletion leads to a reduction in cohesin acetylation and Sororin recruitment to chromatin. In early mitosis, Esco2 deficiency causes changes in the chromosomal localization of cohesin and its protector Sgo1. Our results suggest that Esco2 is needed for cohesin acetylation in PCH and that this modification is required for the proper distribution of cohesin on mitotic chromosomes and for centromeric cohesion.

Esco2 promotes neuronal differentiation by repressing Notch signaling

Esco2 is an acetyltransferase that is required for the establishment of sister chromatid cohesion. Roberts-SC phocomelia (RBS) syndrome caused by the mutations of Esco2 gene, is an autosomal recessive development disorder characterized by growth retardation, limb reduction and craniofacial abnormalities including cleft lip and palate. Here, we show that Esco2 protein co-immunoprecipitates with Notch but not with CBF1. Esco2 represses the transactivational activity of Notch protein in an acetyltransferase-independent manner. Chromatin immunoprecipitation experiments suggest that Esco2 might regulate the activity of NICD-CBF1 via attenuating NICD binding to CBF1 on the promoter of Hes1, the downstream target gene of Notch. Furthermore, we demonstrate that the overexpression of Esco2 promotes the neuronal differentiation of P19 embryonic carcinoma cells and C17.2 neural progenitor cells and the knockdown of Esco2 by siRNA blocks the differentiation. The inhibitory effects of Notch protein on neuronal differentiation of P19 cells was suppressed by Esco2 overexpression. Taken together, our study suggests that Esco2 may play an important role in neurogenesis by attenuating Notch signaling to promote neuronal differentiation.

A zebrafish model of Roberts syndrome reveals that Esco2 depletion interferes with development by disrupting the cell cycle

The human developmental diseases Cornelia de Lange Syndrome (CdLS) and Roberts Syndrome (RBS) are both caused by mutations in proteins responsible for sister chromatid cohesion. Cohesion is mediated by a multi-subunit complex called cohesin, which is loaded onto chromosomes by NIPBL. Once on chromosomes, cohesin binding is stabilized in S phase upon acetylation by ESCO2. CdLS is caused by heterozygous mutations in NIPBL or cohesin subunits SMC1A and SMC3, and RBS is caused by homozygous mutations in ESCO2. The genetic cause of both CdLS and RBS reside within the chromosome cohesion apparatus, and therefore they are collectively known as "cohesinopathies". However, the two syndromes have distinct phenotypes, with differences not explained by their shared ontology. In this study, we have used the zebrafish model to distinguish between developmental pathways downstream of cohesin itself, or its acetylase ESCO2. Esco2 depleted zebrafish embryos exhibit features that resemble RBS, including mitotic defects, craniofacial abnormalities and limb truncations. A microarray analysis of Esco2-depleted embryos revealed that different subsets of genes are regulated downstream of Esco2 when compared with cohesin subunit Rad21. Genes downstream of Rad21 showed significant enrichment for transcriptional regulators, while Esco2-regulated genes were more likely to be involved the cell cycle or apoptosis. RNA in situ hybridization showed that runx1, which is spatiotemporally regulated by cohesin, is expressed normally in Esco2-depleted embryos. Furthermore, myca, which is downregulated in rad21 mutants, is upregulated in Esco2-depleted embryos. High levels of cell death contributed to the morphology of Esco2-depleted embryos without affecting specific developmental pathways. We propose that cell proliferation defects and apoptosis could be the primary cause of the features of RBS. Our results show that mutations in different elements of the cohesion apparatus have distinct developmental outcomes, and provide insight into why CdLS and RBS are distinct diseases.

Can corruption of chromosome cohesion create a conduit to cancer?

Cohesin is a conserved multisubunit protein complex with diverse cellular roles, making key contributions to the coordination of chromosome segregation, the DNA damage response and chromatin regulation by epigenetic mechanisms. Much has been learned in recent years about the roles of cohesin in a physiological context, whereas its potential and emerging role in tumour initiation and/or progression has received relatively little attention. In this Opinion article we examine how cohesin deregulation could contribute to cancer development on the basis of its physiological roles.

A case of severe dysmelia of all extremities

A group of limb reduction defects is defined by congenital absence of either part of limbs. We report an extremely rare case of symmetrical upper limb peromelia (absence of distal bones) and asymmetrical lower limb phocomelia (absence of long bones and a flipper-like appearance of feet) in a female fetus at the 20th week of pregnancy. No other malformations were identified. The prevalence of peromelia and phocomelia is extremely rare, and these malformations can be associated with some candidate genes (e.g. de novo apparently balanced reciprocal translocation 46,XX,t(2;12)(p25.1;q24.1)).

Metastatic alveolar rhabdomyosarcoma in multiple endocrine neoplasia type 2A

Rhabdomyosarcoma (RMS), the most common pediatric soft tissue sarcoma, accounts for 3% of childhood malignancies. Multiple Endocrine Neoplasia (MEN) type 2A is an autosomal dominant syndrome associated with near universal development of medullary thyroid carcinoma. We describe a previously unreported association of MEN-2A with metastatic alveolar RMS and review the literature on associated hereditary cancer predisposition syndromes and current therapeutic options. The high penetrance of malignancy in patients with MEN warrants a heightened suspicion for the development of nonendocrine malignancies. The diagnosis of RMS should prompt consideration of screening for familial genetic syndromes in certain patients.

Diagnostic Overlap between Fanconi Anemia and the Cohesinopathies: Roberts Syndrome and Warsaw Breakage Syndrome

Fanconi anemia (FA) is a recessively inherited disease characterized by multiple symptoms including growth retardation, skeletal abnormalities, and bone marrow failure. The FA diagnosis is complicated due to the fact that the clinical manifestations are both diverse and variable. A chromosomal breakage test using a DNA cross-linking agent, in which cells from an FA patient typically exhibit an extraordinarily sensitive response, has been considered the gold standard for the ultimate diagnosis of FA. In the majority of FA patients the test results are unambiguous, although in some cases the presence of hematopoietic mosaicism may complicate interpretation of the data. However, some diagnostic overlap with other syndromes has previously been noted in cases with Nijmegen breakage syndrome. Here we present results showing that misdiagnosis may also occur with patients suffering from two of the three currently known cohesinopathies, that is, Roberts syndrome (RBS) and Warsaw breakage syndrome (WABS). This complication may be avoided by scoring metaphase chromosomes—in addition to chromosomal breakage—for spontaneously occurring premature centromere division, which is characteristic for RBS and WABS, but not for FA.

Cohesinopathies, gene expression, and chromatin organization

The cohesin protein complex is best known for its role in sister chromatid cohesion, which is crucial for accurate chromosome segregation. Mutations in cohesin proteins or their regulators have been associated with human diseases (termed cohesinopathies). The developmental defects observed in these diseases indicate a role for cohesin in gene regulation distinct from its role in chromosome segregation. In mammalian cells, cohesin stably interacts with specific chromosomal sites and colocalizes with CTCF, a protein that promotes long-range DNA interactions, implying a role for cohesin in genome organization. Moreover, cohesin defects compromise the subnuclear position of chromatin. Therefore, defects in the cohesin network that alter gene expression and genome organization may underlie cohesinopathies.