Ocular features in Rubinstein-Taybi syndrome: investigation of 24 patients and review of the literature

The functional secondary effect after an integrated rehabilitative intervention to learn reading and writing in a girl with Rubinstein-Taybi syndrome

PURPOSE

A case report of a six-year and five-month-old female admitted with typical symptoms of Rubinstein-Taybi syndrome is presented. Clinical and rehabilitation settings where she acquired her reading, writing, and communication skills are described.

METHODS

Because of her cognitive disabilities, a multidisciplinary and long-term intervention (2014-2020) was necessary. Treatment included orthoptic, psychomotor, logopedic, occupational, and neuropsychological care. Her family and school were involved.

RESULTS

Increased attention led to decreased dysfunctional behaviors. Test results are still below average, but there has been significant improvement. Better communication skills resulted from increased phonetic range, improved articulation, lexical-semantic structure, comprehension, and production of sentences. Digital technologies played a significant role in enhancing her communication skills, not just in social interactions but also in school activities. The patient is oriented in time and space with the help of agendas and calendars. She can express her needs and compose concise narratives. As a result of acquiring functional skills, she is better equipped to handle real-life situations, which has led to increased social and family activities.

CONCLUSION

This case report highlights the importance of personalized rehabilitation programs. Obtaining an early genetic diagnosis is crucial for timely tailored rehabilitation, and any delays in this process can hinder progress.

Diagnosis and management in Rubinstein-Taybi syndrome: first international consensus statement

Rubinstein-Taybi syndrome (RTS) is an archetypical genetic syndrome that is characterised by intellectual disability, well-defined facial features, distal limb anomalies and atypical growth, among numerous other signs and symptoms. It is caused by variants in either of two genes (CREBBP, EP300) which encode for the proteins CBP and p300, which both have a function in transcription regulation and histone acetylation. As a group of international experts and national support groups dedicated to the syndrome, we realised that marked heterogeneity currently exists in clinical and molecular diagnostic approaches and care practices in various parts of the world. Here, we outline a series of recommendations that document the consensus of a group of international experts on clinical diagnostic criteria for types of RTS (RTS1: CREBBP; RTS2: EP300), molecular investigations, long-term management of various particular physical and behavioural issues and care planning. The recommendations as presented here will need to be evaluated for improvements to allow for continued optimisation of diagnostics and care.

Congenital pterygium with anterior segment dysgenesis: rare ocular manifestation in Rubinstein-Taybi syndrome

Pterygium is a benign, wing-shaped fibrovascular overgrowth of subconjunctival tissue that can encroach over the cornea. This condition usually occurs in individuals aged 20-40 years but is rarely seen in children. We report a case of an infant with Rubenstein-Taybi syndrome presenting with nebulo-macular corneal opacity and congenital pterygium. On examination under anaesthesia, bilateral infero-nasal nebulo-macular corneal opacity (6 × 5 mm) with a whitish pink tissue originating from nasal bulbar conjunctiva was noticed. The probe test was negative for this tissue. To the best of our knowledge, only two other cases of congenital pterygium have been reported in the literature. The presence of this anomaly supports the hypothesis of genetic factors having a role in the development of pterygium.

Floating-Harbor syndrome with chorioretinal colobomas

BACKGROUND

We present a case of a child with Floating-Harbor Syndrome (FHS) with bilateral chorioretinal coloboma (CC). To the best of our knowledge, this is the first case report of this association. Floating- Harbor syndrome is an extremely rare autosomal dominant genetic disorder with approximately 100 cases reported. It is characterized by a series of atypical features that include short stature with delayed bone age, low birth weight, skeletal anomalies, delayed speech development, and dysmorphic facial characteristics that typically portray a triangular face, deep-set eyes, long eyelashes, and prominent nose.

MATERIALS AND METHODS

Our patient was examined by a pediatric ophthalmologist for the time at age of 7. Visual acuity, optical coherence tomography (OCT) and Optos imaging were collected on every visit. The patient had whole genome sequencing ordered by a pediatric geneticist to confirm Floating-Harbor syndrome.

RESULTS

We present the patient's OCT and Optos images that illustrate the location of the patient's inferior chorioretinal coloboma in both eyes. The whole genome sequencing report collected revealed a heterozygous de novo pathogenic variant in the SRCAP gene, consistent with a Floating-Harbor syndrome diagnosis in the literature.

DISCUSSION

Both genetic and systemic findings are consistent with the diagnosis of Floating-Harbor syndrome in our patient. Rubenstein-Taybi and Floating-Harbor syndrome share a similarity in molecular and physical manifestations, but because of the prevalence in Rubenstein-Taybi diagnoses, it is a syndromic condition that includes coloboma and frequently associated with each other. Therefore, a retinal exam should become part of the standard protocol for those with FHS, as proper diagnosis, examination and treatment can prevent irreversible retinal damage.

Ocular manifestations of congenital anomalies of the kidney and urinary tract (CAKUT)

Congenital anomalies of the kidney and urinary tract (CAKUT) are among the most common birth defects worldwide and a major cause of kidney failure in children. Extra-renal manifestations are also common. This study reviewed diseases associated with the Genomics England CAKUT-associated gene panel for ocular anomalies. In addition, each gene was examined for expression in the human retina and an ocular phenotype in mouse models using the Human Protein Atlas and Mouse Genome Informatics databases, respectively. Thirty-four (54%) of the 63 CAKUT-associated genes (55 'green' and 8 'amber') had a reported ocular phenotype. Five of the 6 most common CAKUT-associated genes (PAX2, EYA1, SALL1, GATA3, PBX1) that represent 30% of all diagnoses had ocular features. The ocular abnormalities found with most CAKUT-associated genes and with five of the six commonest were coloboma, microphthalmia, optic disc anomalies, refraction errors (astigmatism, myopia, and hypermetropia), and cataract. Seven of the CAKUT-associated genes studied (11%) had no reported ocular features but were expressed in the human retina or had an ocular phenotype in a mouse model, which suggested further possibly-unrecognised abnormalities. About one third of CAKUT-associated genes (18, 29%) had no ocular associations and were not expressed in the retina, and the corresponding mouse models had no ocular phenotype. Ocular abnormalities in individuals with CAKUT suggest a genetic basis for the disease and sometimes indicate the affected gene. Individuals with CAKUT often have ocular abnormalities and may require an ophthalmic review, monitoring, and treatment to preserve vision.

Secondary developmental glaucoma

The basic pathophysiology of all childhood glaucoma results from impaired outflow through the trabecular meshwork. Anterior Segment Dysgeneses (ASD) are a group of nonacquired anomalies associated with secondary developmental glaucoma, characterized by impaired development of the structures of the anterior segment. Many genes impact the development of the anterior segment. The cause of the development of the abnormalities is thought to be multifactorial. Molecular research has helped our understanding of the molecular basis of ASD and the developmental mechanisms underlying these conditions. Identifying the genetic changes underlying ASD has gradually led to the recognition that some of these conditions may be parts of a disease spectrum rather than isolated anomalies. The characterization of the underlying genetic abnormalities responsible for glaucoma is the first step toward developing diagnostic and screening tests, which could identify individuals at risk for disease before irreversible optic nerve damage occurs. It is also crucial for genetic counseling and risk stratification of later pregnancies. It also aids prenatal testing by various methods allowing for effective genetic counseling. This review summarizes various ocular and systemic conditions that result in secondary developmental glaucoma and provide an overview of the phenotypes, the diagnosis and principles of management of the various disorders.

De novo variation in EP300 gene cause Rubinstein-Taybi syndrome 2 in a Chinese family with severe early-onset high myopia

BACKGROUND

Rubinstein-Taybi syndrome (RSTS) is characterized by distinctive facial features, broad and often angulated thumbs and halluces, short stature, and moderate-to-severe intellectual disability, classified into two types RSTS1 (CREBBP-RSTS) and RSTS2 (EP300-RSTS). More often, the clinical features are inconclusive and the diagnosis of RSTS is established in a proband with identification of a heterozygous pathogenic variant in CREBBP or EP300 to confirm the diagnosis.

METHODS

In this study, to describe an association between the clinical phenotype and the genotype of a RSTS2 patient who was initially diagnosed with severe early-onset high myopia (eoHM) from a healthy Chinese family, we tested the proband of this family by whole exome sequencing (WES) and further verified among other family members by Sanger sequencing. Real-time quantitative PCR was used to detect differences in the relative mRNA expression of candidate genes available in the proband and family members. Comprehensive ophthalmic tests as well as other systemic examinations were also performed on participants with various genotypes.

RESULTS

Whole-exome sequencing revealed that the proband carried the heterozygous frameshift deletion variant c.3714_3715del (p.Leu1239Glyfs*3) in the EP300 gene, which was not carried by the normal parents and young sister as verified by Sanger sequencing, indicating that the variant was de novo. Real-time quantitative PCR showed that the mRNA expression of EP300 gene was lower in the proband than in other normal family members, indicating that such a variant caused an effect on gene function at the mRNA expression level. The variant was classified as pathogenic as assessed by the interpretation principles of HGMD sequence variants and ACMG guidelines. According to ACMG guidelines, the heterozygous frameshift deletion variant c.3714_3715del (p.Leu1239Glyfs*3) in the EP300 gene was more likely the pathogenic variant of this family with RSTS2.

CONCLUSIONS

Therefore, in this paper, we first report de novo heterozygous variation in EP300 causing eoHM-RSTS. Our study extends the genotypic spectrums for EP300-RSTS and better assists physicians in predicting, diagnosis, genetic counseling, eugenics guidance and gene therapy for EP300-RSTS.

Evaluation of Ayres Sensory Integration® Intervention on Sensory Processing and Motor Function in a Child with Rubinstein-Taybi Syndrome: A Case Report

The Rubinstein-Taybi Syndrome (RSTS) literature is limited about sensory integration, which is a foundational neurological function of the central nervous system that may affect the development of cognitive, social, and motor skills. The aim of this case report was to investigate the effects of Ayres Sensory Integration^® (ASI) intervention on processing and integrating sensations, motor functions and parental goals of 3-year-old child with RSTS. Analysis of assessment data reviewed before and after treatment. Assessment collected by interview, Sensory Profile (SP), Sensory Processing Measure-Preschool (SPM-P) Home, Peabody Developmental Motor Scales-2 (PDMS-2), Gross Motor Function Measurement-88 (GMFM-88), and Gross Motor Function Classification System (GMFCS). Progress toward goals and objectives was measured with Goal Attainment Scale (GAS). ASI intervention was implemented 3 times per week for 8 weeks. At pre-intervention, SP and SPM-P Home revealed prominent sensory processing and integration difficulties in this case. PDMS-2 scores indicated the child was far behind his peers in fine and gross motor areas. In addition, systematic observations determined that the child's GMFCS level was III. After 8 weeks of ASI intervention significant improvements were found in parent reports of sensory processing in the areas of vestibular, tactile, and oral functioning on the Sensory Profile. Gains in functional motor skills were found on the GMFM-88 and the GMFCS. Consistent with these results, significant gains at or above expected levels of performance were found on GAS goals which reflected the family's main concerns for social participation, feeding, play, and movement. There are limited studies on sensory processing and integration in children with RSTS. This case report identified sensory processing and integration difficulties for the first time in a child with RSTS. Results also provide preliminary support for the positive effects of ASI intervention on sensory processing, functional motor skills, and parental goals of a child with RSTS.

Congenital glaucoma as a presenting feature of Rubinstein-Taybi syndrome in an infant with a novel pathogenic variant in the CREBBP gene

Rubinstein-Taybi syndrome, also known as broad thumb-hallux syndrome, is a rare autosomal dominant genetic disorder. This multiorgan syndrome is linked to a pathogenic mutation in the CREBBP or EBP300 genes.We present a patient with a hitherto unreported constellation of anterior segment abnormalities, including congenital glaucoma, congenital corneal keloid, cataract, and distinct facial and systemic features including a high-arched palate, low-set posteriorly rotated ears, Café-au-lait spots on the back, broad terminal phalanges of hands and feet, and bilateral cryptorchidism. The characteristic dysgenetic angle features and ultrasound biomicroscopic findings described in this case report show the occurrence of concomitant congenital keloid with glaucoma.Genetic testing revealed a heterozygous one-base pair duplication in exon 3 of the CREBBP gene (c.886dupC), a novel frameshift pathogenic mutation in the CREBBP gene that has not been previously reported in a clinical setting.

Tooth number abnormality: from bench to bedside

Tooth number abnormality is one of the most common dental developmental diseases, which includes both tooth agenesis and supernumerary teeth. Tooth development is regulated by numerous developmental signals, such as the well-known Wnt, BMP, FGF, Shh and Eda pathways, which mediate the ongoing complex interactions between epithelium and mesenchyme. Abnormal expression of these crutial signalling during this process may eventually lead to the development of anomalies in tooth number; however, the underlying mechanisms remain elusive. In this review, we summarized the major process of tooth development, the latest progress of mechanism studies and newly reported clinical investigations of tooth number abnormality. In addition, potential treatment approaches for tooth number abnormality based on developmental biology are also discussed. This review not only provides a reference for the diagnosis and treatment of tooth number abnormality in clinical practice but also facilitates the translation of basic research to the clinical application.

Quality of life of Brazilian families who have children with Rubinstein-Taybi syndrome: An exploratory cross-sectional study

This exploratory cross-sectional study aimed to examine the family quality of life (FQoL) among 51 Brazilian families who have children with Rubinstein-Taybi syndrome, a rare genetic disorder. Data were collected using sociodemographic and clinical data forms, as well as the Beach Center FQoL Scale, a 5-point Likert scale ranging from "very dissatisfied" (1) to "very satisfied" (5). The average score of the overall FQoL was 3.93 ± 0.64. Families' scores were higher for family interaction (4.17 ± 0.76), parenting (4.13 ± 0.61), and disability-related support (4.08 ± 0.76) domains, and lower for the family's emotional well-being (3.31 ± 0.96) and physical/material well-being (3.76 ± 0.82) domains. Family income, attendance at religious services, presence of ocular abnormalities, and aggressive behavior explained 46.2% of the variance in the overall FQoL. In summary, FQoL seems to be anchored in aspects such as family interaction and the care of parents, and be negatively affected by emotional issues, physical, and material limitations. In this context, psychological assistance should be provided to both parents and siblings whenever indicated, for improving emotional well-being and increasing family resilience. Additionally, investments in social policies, services, and human and material resources are needed to improve the physical and material conditions of families, promote better health care, and therefore reduce the family burden.

Rubinstein-Taybi Syndrome: Presentation in the First Month of Life

This web-based survey of 311 respondents from 25 countries provides additional information about the early presentation of Rubinstein-Taybi syndrome. Most (86%) infants present during the neonatal period, with 69% of these within 24 hours of life. Prolonged hospital stay is common (61%).

A novel CREBBP mutation and its phenotype in a case of Rubinstein–Taybi syndrome

Background

This study was to report a novel CREBBP mutation and phenotype in a child with Rubinstein–Taybi syndrome.

Methods

Case report of a 9-year-old boy.

Results

We described the patient’s clinical manifestations in detail, and found that in addition to the typical systemic manifestations of the syndrome, the outstanding manifestation of the child was severe intellectual deficiency and prominent ocular abnormalities. Whole-exome sequencing and sanger sequencing were performed on the patient and his parents, a large intragenic deletion, covering the exon 1 region and part of the intron 1 region of the TRAP1 gene, and the entire region from intron 27 to exon 30 of the CREBBP gene (chr16:3745393-3783894) was identified on the patient. This mutation affected the CREBBP histone acetyltransferase (HAT) domain.

Conclusions

This findings in our patient add to the spectrum of genetic variants described in Rubinstein–Taybi syndrome and present a RSTS patient with various ocular anomalies including early onset glaucoma.

The natural history of adults with Rubinstein-Taybi syndrome: a families-reported experience

The existing knowledge about morbidity in adults with Rubinstein-Taybi syndrome (RTS) is limited and detailed data on their natural history and response to management are needed for optimal care in later life. We formed an international, multidisciplinary working group that developed an accessible questionnaire including key issues about adults with RTS and disseminated this to all known RTS support groups via social media. We report the observations from a cohort of 87 adult individuals of whom 43 had a molecularly confirmed diagnosis. The adult natural history of RTS is defined by prevalent behavioural/psychiatric problems (83%), gastrointestinal problems (73%) that are represented mainly by constipation; and sleep problems (62%) that manifest in a consistent pattern of sleep apnoea, difficulty staying asleep and an increased need for sleep. Furthermore, over than half of the RTS individuals (65%) had skin and adnexa-related problems. Half of the individuals receive multidisciplinary follow-up and required surgery at least once, and most frequently more than once, during adulthood. Our data confirm that adults with RTS enjoy both social and occupational possibilities, show a variegated experience of everyday life but experience a significant morbidity and ongoing medical issues which do not appear to be as coordinated and multidisciplinary managed as in paediatric patients. We highlight the need for optimal care in a multidisciplinary setting including the pivotal role of specialists for adult care.

Rubinstein-Taybi Syndrome: A Model of Epigenetic Disorder

The Rubinstein-Taybi syndrome (RSTS) is a rare congenital developmental disorder characterized by a typical facial dysmorphism, distal limb abnormalities, intellectual disability, and many additional phenotypical features. It occurs at between 1/100,000 and 1/125,000 births. Two genes are currently known to cause RSTS, CREBBP and EP300, mutated in around 55% and 8% of clinically diagnosed cases, respectively. To date, 500 pathogenic variants have been reported for the CREBBP gene and 118 for EP300. These two genes encode paralogs acting as lysine acetyltransferase involved in transcriptional regulation and chromatin remodeling with a key role in neuronal plasticity and cognition. Because of the clinical heterogeneity of this syndrome ranging from the typical clinical diagnosis to features overlapping with other Mendelian disorders of the epigenetic machinery, phenotype/genotype correlations remain difficult to establish. In this context, the deciphering of the patho-physiological process underlying these diseases and the definition of a specific episignature will likely improve the diagnostic efficiency but also open novel therapeutic perspectives. This review summarizes the current clinical and molecular knowledge and highlights the epigenetic regulation of RSTS as a model of chromatinopathy.

Ontogenesis of the tear drainage system requires Prickle1-driven polarized basement membrane deposition

In terrestrial animals, the lacrimal drainage apparatus evolved to serve as conduits for tear flow; however, little is known about the ontogenesis of this system. Here, we define the anatomy of the fully formed tear duct in mice, characterize crucial morphogenetic events for the development of tear duct components and identify the site for primordial tear duct (PTD) initiation. We report that the PTD originates from the orbital lacrimal lamina, a junction formed by the epithelia of the maxillary and lateral nasal processes. We demonstrate that Prickle1, a key component of planar cell polarity signaling, is expressed in progenitors of the PTD and throughout tear duct morphogenesis. Disruption of Prickle1 stalls tear duct elongation; in particular, the loss of basement membrane deposition and aberrant cytoplasmic accumulation of laminin are salient. Altered cell adhesion, cytoskeletal transport systems, vesicular transport systems and cell axis orientation in Prickle1 mutants support the role of Prickle1 in planar cell polarity. Taken together, our results highlight a crucial role of Prickle1-mediated polarized basement membrane secretion and deposition in PTD elongation.

Novel Findings in Floating-Harbor Syndrome and a Mini-Review of the Literature

Floating-Harbor syndrome (FHS) is a rare autosomal dominant genetic disorder characterized by proportionate short stature with delayed bone maturation, lack of expressive language, and distinctive facial features including a large nose, long eyelashes, deeply set eyes, and triangular face. Mutations in the SRCAP gene cause truncated SNF2-related CREBBP activator protein (SRCAP) and lead to FHS. SRCAP is one of several proteins that act as coactivator for the CREB-binding protein which is associated with Rubinstein-Taybi syndrome (RSTS). This condition likely explains the phenotypic overlap between FHS and RSTS. Herein, we report on a patient with FHS who also had dystrophic toenails, preauricular skin tag, and nasolacrimal duct obstruction which is also defined in patients with RSTS. In summary, the fact that especially nasolacrimal duct obstruction has also been observed in RSTS reinforces the idea that this finding is one of the features of FHS. Assessment of the lacrimal system and examination of skin and nails should be suggested in patients with FHS.

Malformation of Tear Ducts Underlies the Epiphora and Precocious Eyelid Opening in Prickle 1 Mutant Mice: Genetic Implications for Tear Duct Genesis

Purpose

Obstruction of the tear drainage causes a range of ocular surface disorders. Hitherto, the genetics of tear duct development and obstruction has been scarcely explored, and related animal models are lacking. This study aims to study the potential role of the Wnt/PCP pathway mediated by Prickle 1 in tear duct development and diseases.

Methods

A severe hypomorphic Prickle 1 mutant was generated. Histology and immunohistochemistry were performed to compare wild type, Prickle 1 hypomorphic, and null mutant tear ducts. In situ hybridization was conducted to identify the signaling components in the developing tear ducts. Three-dimensional (3D) reconstruction was used to detect the human embryonic tear duct.

Results

Here, we report that a severe Prickle 1 hypomorph mouse line exhibited epiphora. This phenotype was due to the blockage of the tear drainage by incompletely formed nasolacrimal duct (NLD) and lacrimal canaliculi (LC), which also causes precocious eyelid opening. We observed a dose-dependent requirement of Prickle 1 for tear duct outgrowth. An investigation of the expression of Wnt/PCP core genes demonstrated a subset of PCP signaling components expressed in the developing tear duct. Furthermore, Prickle 1 is not required for the expression of Fgfr2/Fgf10 and p63 genes, which are associated with the NLD and LC hypoplasia in humans. Last, we showed that Prickle 1 expression in the developing tear drainage system is conserved between mice and humans.

Conclusions

The study suggests that malformed tear ducts caused by disruption of Prickle 1 underlies the epiphora and precocious eyelid opening.

Rubinstein-Taybi syndrome in diverse populations

Rubinstein-Taybi syndrome (RSTS) is an autosomal dominant disorder, caused by loss-of-function variants in CREBBP or EP300. Affected individuals present with distinctive craniofacial features, broad thumbs and/or halluces, and intellectual disability. RSTS phenotype has been well characterized in individuals of European descent but not in other populations. In this study, individuals from diverse populations with RSTS were assessed by clinical examination and facial analysis technology. Clinical data of 38 individuals from 14 different countries were analyzed. The median age was 7 years (age range: 7 months to 47 years), and 63% were females. The most common phenotypic features in all population groups included broad thumbs and/or halluces in 97%, convex nasal ridge in 94%, and arched eyebrows in 92%. Face images of 87 individuals with RSTS (age range: 2 months to 47 years) were collected for evaluation using facial analysis technology. We compared images from 82 individuals with RSTS against 82 age- and sex-matched controls and obtained an area under the receiver operating characteristic curve (AUC) of 0.99 (p < .001), demonstrating excellent discrimination efficacy. The discrimination was, however, poor in the African group (AUC: 0.79; p = .145). Individuals with EP300 variants were more effectively discriminated (AUC: 0.95) compared with those with CREBBP variants (AUC: 0.93). This study shows that clinical examination combined with facial analysis technology may enable earlier and improved diagnosis of RSTS in diverse populations.

Lacrimal drainage anomalies in Rubinstein-Taybi syndrome: case report and review of literature

Rubinstein-Taybi syndrome is a rare multisystem disorder characterized by broad thumbs and first toes, short stature, microcephaly, delayed milestones, beak nose, and hypertelorism. Lacrimal drainage anomalies are not uncommon in this syndrome. We present a patient with Rubinstein-Taybi syndrome with bilateral congenital nasolacrimal duct obstruction and left-sided grossly dilated nasolacrimal duct.

Dynamic genome wide expression profiling of Drosophila head development reveals a novel role of Hunchback in retinal glia cell development and blood-brain barrier integrity

Drosophila melanogaster head development represents a valuable process to study the developmental control of various organs, such as the antennae, the dorsal ocelli and the compound eyes from a common precursor, the eye-antennal imaginal disc. While the gene regulatory network underlying compound eye development has been extensively studied, the key transcription factors regulating the formation of other head structures from the same imaginal disc are largely unknown. We obtained the developmental transcriptome of the eye-antennal discs covering late patterning processes at the late 2^nd larval instar stage to the onset and progression of differentiation at the end of larval development. We revealed the expression profiles of all genes expressed during eye-antennal disc development and we determined temporally co-expressed genes by hierarchical clustering. Since co-expressed genes may be regulated by common transcriptional regulators, we combined our transcriptome dataset with publicly available ChIP-seq data to identify central transcription factors that co-regulate genes during head development. Besides the identification of already known and well-described transcription factors, we show that the transcription factor Hunchback (Hb) regulates a significant number of genes that are expressed during late differentiation stages. We confirm that hb is expressed in two polyploid subperineurial glia cells (carpet cells) and a thorough functional analysis shows that loss of Hb function results in a loss of carpet cells in the eye-antennal disc. Additionally, we provide for the first time functional data indicating that carpet cells are an integral part of the blood-brain barrier. Eventually, we combined our expression data with a de novo Hb motif search to reveal stage specific putative target genes of which we find a significant number indeed expressed in carpet cells.

The development of different cell types must be tightly coordinated, and the eye-antennal imaginal discs of Drosophila melanogaster represent an excellent model to study the molecular mechanisms underlying this coordination. These imaginal discs contain the anlagen of nearly all adult head structures, such as the antennae, the head cuticle, the ocelli and the compound eyes. While large scale screens have been performed to unravel the gene regulatory network underlying compound eye development, a comprehensive understanding of genome wide expression dynamics throughout head development is still missing to date. We studied the genome wide gene expression dynamics during eye-antennal disc development in D. melanogaster to identify new central regulators of the underlying gene regulatory network. Expression based gene clustering and transcription factor motif enrichment analyses revealed a central regulatory role of the transcription factor Hunchback (Hb). We confirmed that hb is expressed in two polyploid retinal subperineurial glia cells (carpet cells). Our functional analysis shows that Hb is necessary for carpet cell development and we show for the first time that the carpet cells are an integral part of the blood-brain barrier.

Syndromic and Nonsyndromic Systemic Associations of Congenital Lacrimal Drainage Anomalies: A Major Review

PURPOSE

To review and summarize the syndromic, nonsyndromic, and systemic associations of congenital lacrimal drainage anomalies.

METHODS

The authors performed a PubMed search of all articles published in English on congenital lacrimal anomalies (1933-2016). Patients of these articles were reviewed along with the literature of direct references to syndromes and other systemic associations. Data reviewed included syndromic descriptions, systemic details, demographics, lacrimal presentations, management, and outcomes.

RESULTS

Syndromic and systemic associations with congenital lacrimal drainage disorders are not known to be common. Although familial presentations have been reported, the inheritance patterns are unclear for most anomalies. There is an increasingly growing evidence of a genetic basis to many lacrimal anomalies. However, few syndromes have either widespread or are frequently associated with lacrimal anomalies. Few sequences of distinct lacrimal presentations and intraoperative findings are seen. Surgical challenges in these patients are distinct and a thorough pre and intraoperative anatomical assessment, detailed imaging when indicated, and assessment and correction of associated periocular and facial abnormalities may facilitate good outcomes.

CONCLUSIONS

Lacrimal drainage anomalies associated with syndromic and nonsyndromic systemic conditions have certain unique features of their own and their surgical and anesthesia challenges are distinct. Diagnosis of congenital lacrimal drainage anomalies should prompt consideration of the possible presence of associated systemic abnormalities.

Mosaic CREBBP mutation causes overlapping clinical features of Rubinstein-Taybi and Filippi syndromes

Rubinstein-Taybi syndrome (RTS, OMIM 180849) and Filippi syndrome (FLPIS, OMIM 272440) are both rare syndromes, with multiple congenital anomalies and intellectual deficit (MCA/ID). We present a patient with intellectual deficit, short stature, bilateral syndactyly of hands and feet, broad thumbs, ocular abnormalities, and dysmorphic facial features. These clinical features suggest both RTS and FLPIS. Initial DNA analysis of DNA isolated from blood did not identify variants to confirm either of these syndrome diagnoses. Whole-exome sequencing identified a homozygous variant in C9orf173, which was novel at the time of analysis. Further Sanger sequencing analysis of FLPIS cases tested negative for CKAP2L variants did not, however, reveal any further variants. Subsequent analysis using DNA isolated from buccal mucosa revealed a mosaic variant in CREBBP. This report highlights the importance of excluding mosaic variants in patients with a strong but atypical clinical presentation of a MCA/ID syndrome if no disease-causing variants can be detected in DNA isolated from blood samples. As the striking syndactyly observed in the present case is typical for FLPIS, we suggest CREBBP analysis in saliva samples for FLPIS syndrome cases in which no causal CKAP2L variant is detected.

Ultra-Rare Syndromes: The Example of Rubinstein-Taybi Syndrome

Rubinstein-Taybi syndrome (RSTS) is a rare, congenital, plurimalformative, and neurodevelopmental disorder. Clinical diagnosis can be complicated by the heterogeneous clinical presentation and the lack of a consensus list of diagnostic criteria, and it is confirmed by molecular tests in approximately 55 to 78% of cases. The etiology is partially known with mutations in two functionally related genes: CREBBP and EP300. Notwithstanding the knowledge on clinical, genetic, and allelic heterogeneity, no clear genotype-phenotype correlation has yet been established. Standardized guidelines for the management of pediatric patients are available and therapy for RSTS patients is currently only symptomatic. In this article, several clinic and genetic aspects of RSTS are critically reviewed.

Rare Diseases Leading to Childhood Glaucoma: Epidemiology, Pathophysiogenesis, and Management

Noteworthy heterogeneity exists in the rare diseases associated with childhood glaucoma. Primary congenital glaucoma is mostly sporadic; however, 10% to 40% of cases are familial. CYP1B1 gene mutations seem to account for 87% of familial cases and 27% of sporadic cases. Childhood glaucoma is classified in primary and secondary congenital glaucoma, further divided as glaucoma arising in dysgenesis associated with neural crest anomalies, phakomatoses, metabolic disorders, mitotic diseases, congenital disorders, and acquired conditions. Neural crest alterations lead to the wide spectrum of iridocorneal trabeculodysgenesis. Systemic diseases associated with childhood glaucoma include the heterogenous group of phakomatoses where glaucoma is frequently encountered in the Sturge-Weber syndrome and its variants, in phakomatosis pigmentovascularis associated with oculodermal melanocytosis, and more rarely in neurofibromatosis type 1. Childhood glaucoma is also described in systemic disorders of mitotic and metabolic activity. Acquired secondary glaucoma has been associated with uveitis, trauma, drugs, and neoplastic diseases. A database research revealed reports of childhood glaucoma in rare diseases, which do not include glaucoma in their manifestation. These are otopalatodigital syndrome, complete androgen insensitivity, pseudotrisomy 13, Brachmann-de Lange syndrome, acrofrontofacionasal dysostosis, caudal regression syndrome, and Wolf-Hirschhorn syndrome.

Drosophila Eye Model to Study Neuroprotective Role of CREB Binding Protein (CBP) in Alzheimer's Disease

BACKGROUND

The progressive neurodegenerative disorder Alzheimer's disease (AD) manifests as loss of cognitive functions, and finally leads to death of the affected individual. AD may result from accumulation of amyloid plaques. These amyloid plaques comprising of amyloid-beta 42 (Aβ42) polypeptides results from the improper cleavage of amyloid precursor protein (APP) in the brain. The Aβ42 plaques have been shown to disrupt the normal cellular processes and thereby trigger abnormal signaling which results in the death of neurons. However, the molecular-genetic mechanism(s) responsible for Aβ42 mediated neurodegeneration is yet to be fully understood.

METHODOLOGY/PRINCIPAL FINDINGS

We have utilized Gal4/UAS system to develop a transgenic fruit fly model for Aβ42 mediated neurodegeneration. Targeted misexpression of human Aβ42 in the differentiating photoreceptor neurons of the developing eye of transgenic fly triggers neurodegeneration. This progressive neurodegenerative phenotype resembles Alzheimer's like neuropathology. We identified a histone acetylase, CREB Binding Protein (CBP), as a genetic modifier of Aβ42 mediated neurodegeneration. Targeted misexpression of CBP along with Aβ42 in the differentiating retina can significantly rescue neurodegeneration. We found that gain-of-function of CBP rescues Aβ42 mediated neurodegeneration by blocking cell death. Misexpression of Aβ42 affects the targeting of axons from retina to the brain but misexpression of full length CBP along with Aβ42 can restore this defect. The CBP protein has multiple domains and is known to interact with many different proteins. Our structure function analysis using truncated constructs lacking one or more domains of CBP protein, in transgenic flies revealed that Bromo, HAT and polyglutamine (BHQ) domains together are required for the neuroprotective function of CBP. This BHQ domain of CBP has not been attributed to promote survival in any other neurodegenerative disorders.

CONCLUSIONS/SIGNIFICANCE

We have identified CBP as a genetic modifier of Aβ42 mediated neurodegeneration. Furthermore, we have identified BHQ domain of CBP is responsible for its neuroprotective function. These studies may have significant bearing on our understanding of genetic basis of AD.

Exome Sequencing Identification of EP300 Mutation in a Proband with Coloboma and Imperforate Anus: Possible Expansion of the Phenotypic Spectrum of Rubinstein-Taybi Syndrome

Rubinstein-Taybi syndrome (RSTS) is a multisystem developmental disorder characterized by facial dysmorphisms, broad thumbs and halluces, growth retardation, and intellectual disability. In about 8% of RSTS cases, mutations are found in EP300. Previously, the EP300 mutation has been shown to cause the highly variable RSTS phenotype. Using exome sequencing, we identified a de novo EP300 frameshift mutation in a proband with coloboma, facial asymmetry and imperforate anus with minimal RSTS features. Previous molecular studies have demonstrated the importance of EP300 in oculogenesis, supporting the possibility that EP300 mutation may cause ocular coloboma. Since a wide phenotypic spectrum is well known in EP300-associated RSTS cases, the atypical phenotype identified in our proband may be an example of rare manifestations of RSTS.

Expanding the phenotypic spectrum in EP300-related Rubinstein-Taybi syndrome

Rubinstein-Taybi syndrome (RSTS) can be caused by heterozygous mutations or deletions involving CREBBP or, less commonly, EP300. To date, only 15 patients with EP300 mutations have been clinically described. Frequently reported manifestations in these patients include characteristic facial and limb features, varying degrees of neurocognitive dysfunction, and maternal preeclampsia. Other congenital anomalies are less frequently reported. We describe a child found to have a de novo EP300 mutation (c.4933C>T, predicted to result in p.Arg1645X) through research-based whole-genome sequencing of the family trio. The child's presentation involved dysmorphic features as well as unilateral renal agenesis, a myelomeningocele, and minor genitourinary anomalies. The involvement of congenital anomalies in all 16 clinically described patients with EP300 mutations (25% of which have been identified by "hypothesis free" methods, including microarray, exome, and whole-genome sequencing) is reviewed. In summary, genitourinary anomalies have been identified in 38%, cardiovascular anomalies in 25%, spinal/vertebral anomalies in 19%, other skeletal anomalies in 19%, brain anomalies in 13%, and renal anomalies in 6%. Our patient expands the phenotypic spectrum in EP300-related RSTS; this case demonstrates the evolving practice of clinical genomics related to increasing availability of genomic sequencing methods.

Rubinstein-Taybi syndrome: clinical features, genetic basis, diagnosis, and management

Background

Rubinstein-Taybi syndrome (RSTS) is an extremely rare autosomal dominant genetic disease, with an estimated prevalence of one case per 125,000 live births. RSTS is characterized by typical facial features, microcephaly, broad thumbs and first toes, intellectual disability, and postnatal growth retardation. However, no standard diagnostic criteria are available for RSTS. In this review, we summarized the clinical features and genetic basis of RSTS and highlighted areas for future studies on an appropriate diagnostic protocol and follow-up care for RSTS.

Discussion

RSTS is primarily characterized by delayed growth in height and weight, microcephaly, dysmorphic facial features, and broad thumbs and big toe. Over 90% RSTS individuals with disabilities survive to adulthood, but healthcare for these patients is particularly complex, time-consuming, and costly. In addition, no standard diagnostic criteria and follow-up care guidelines are available for RSTS. It has been shown that mutations in the genes encoding the cyclic-AMP-regulated enhancer binding protein (CREBBP) and the E1A-binding protein p300 (EP300) contributed to the development of RSTS. Therefore, genetic tests are useful for the diagnosis of RSTS, although most RSTS cases are currently diagnosed based on clinical features.

Summary

The clinical features of RSTS have been extensively studied, which significantly contributes to the diagnosis of this extremely rare syndrome. However, the pathogenesis and genotype-phenotype associations of RSTS are largely unknown. Therefore, multicenter studies and international cooperation are highlighted for better understanding of this disease, establishing standard diagnostic criteria, and providing professional management and follow-up care of RSTS.

Keloids in Rubinstein-Taybi syndrome: a clinical study

BACKGROUND

Rubinstein-Taybi syndrome (RSTS) is a multiple congenital anomalies-intellectual disability syndrome. One of the complications is keloid formation. Keloids are proliferative fibrous growths resulting from excessive tissue response to skin trauma.

OBJECTIVES

To describe the clinical characteristics of keloids in individuals with RSTS reported in the literature and in a cohort of personally evaluated individuals with RSTS.

PATIENTS AND METHODS

We performed a literature search for descriptions of RSTS individuals with keloids. All known individuals with RSTS in the Netherlands filled out three dedicated questionnaires. All individuals with (possible) keloids were personally evaluated. A further series of individuals with RSTS from the U.K. was personally evaluated.

RESULTS

Reliable data were available for 62 of the 83 Dutch individuals with RSTS and showed 15 individuals with RSTS (24%) to have keloids. The 15 Dutch and 12 U.K. individuals with RSTS with keloids demonstrated that most patients have multiple keloids (n > 1: 82%; n > 5: 30%). Mean age of onset is 11·9 years. The majority of keloids are located on the shoulders and chest. The mean length × width of the largest keloid was 7·1 × 2·8 cm, and the mean thickness was 0·7 cm. All affected individuals complained of itching. Generally, treatment results were disappointing.

CONCLUSIONS

Keloids occur in 24% of individuals with RSTS, either spontaneously or after a minor trauma, usually starting in early puberty. Management schedules have disappointing results. RSTS is a Mendelian disorder with a known molecular basis, and offers excellent opportunities to study the pathogenesis of keloids in general and to search for possible treatments.

Histone posttranslational modifications and cell fate determination: lens induction requires the lysine acetyltransferases CBP and p300

Lens induction is a classical embryologic model to study cell fate determination. It has been proposed earlier that specific changes in core histone modifications accompany the process of cell fate specification and determination. The lysine acetyltransferases CBP and p300 function as principal enzymes that modify core histones to facilitate specific gene expression. Herein, we performed conditional inactivation of both CBP and p300 in the ectodermal cells that give rise to the lens placode. Inactivation of both CBP and p300 resulted in the dramatic discontinuation of all aspects of lens specification and organogenesis, resulting in aphakia. The CBP/p300^−/− ectodermal cells are viable and not prone to apoptosis. These cells showed reduced expression of Six3 and Sox2, while expression of Pax6 was not upregulated, indicating discontinuation of lens induction. Consequently, expression of αB- and αA-crystallins was not initiated. Mutant ectoderm exhibited markedly reduced levels of histone H3 K18 and K27 acetylation, subtly increased H3 K27me3 and unaltered overall levels of H3 K9ac and H3 K4me3. Our data demonstrate that CBP and p300 are required to establish lens cell-type identity during lens induction, and suggest that posttranslational histone modifications are integral to normal cell fate determination in the mammalian lens.

Keratoglobus

Keratoglobus is a rare noninflammatory corneal thinning disorder characterised by generalised thinning and globular protrusion of the cornea. It was first described as a separate clinical entity by Verrey in 1947. Both congenital and acquired forms have been shown to occur, and may be associated with various other ocular and systemic syndromes including the connective tissue disorders. Similarities have been found with other noninflammatory thinning disorders like keratoconus that has given rise to hypotheses about the aetiopathogenesis. However, the exact genetics and pathogenesis are still unclear. Clinical presentation is characterised by progressive diminution resulting from irregular corneal topography with increased corneal fragility due to extreme thinning. Conservative and surgical management for visual rehabilitation and improved tectonic stability have been described, but remains challenging. In the absence of a definitive standard procedure for management of this disorder, various surgical procedures have been attempted in order to overcome the difficulties. This article reviews the aetiological factors, differential diagnosis, histopathology, and management options of keratoglobus.

Transcription coactivators p300 and CBP are necessary for photoreceptor-specific chromatin organization and gene expression

Rod and cone photoreceptor neurons in the mammalian retina possess specialized cellular architecture and functional features for converting light to a neuronal signal. Establishing and maintaining these characteristics requires appropriate expression of a specific set of genes, which is tightly regulated by a network of photoreceptor transcription factors centered on the cone-rod homeobox protein CRX. CRX recruits transcription coactivators p300 and CBP to acetylate promoter-bound histones and activate transcription of target genes. To further elucidate the role of these two coactivators, we conditionally knocked out Ep300 and/or CrebBP in differentiating rods or cones, using opsin-driven Cre recombinase. Knockout of either factor alone exerted minimal effects, but loss of both factors severely disrupted target cell morphology and function: the unique nuclear chromatin organization seen in mouse rods was reversed, accompanied by redistribution of nuclear territories associated with repressive and active histone marks. Transcription of many genes including CRX targets was severely impaired, correlating with reduced histone H3/H4 acetylation (the products of p300/CBP) on target gene promoters. Interestingly, the presence of a single wild-type allele of either coactivator prevented many of these defects, with Ep300 more effective than Cbp. These results suggest that p300 and CBP play essential roles in maintaining photoreceptor-specific structure, function and gene expression.

Aphonia, microstomia, deafness, retinal dystrophy, duplicated halluces and intellectual disability

We report on a sister and brother born to healthy, double first cousin Iranian parents with a seemingly unique combination of signs and symptoms consisting of intellectual disability, congenital absent voice (aphonia), hearing loss, optic atrophy, retinal dystrophy, mildly broad thumbs, and duplicated halluces. Their facial morphology was unusual: thick eyebrows, ptosis, full eyelashes, long palpebral fissures, downslanting palpebral fissures, small mouth, and low-set, posteriorly rotated ears. This phenotype does not meet the diagnostic criteria of any known entity. Because of parental consanguinity, absence of manifestations in parents, and occurrence in sibs of opposite sex, an autosomal recessive pattern of inheritance is likely.

Fluorescein angiography findings in a case of Rubinstein-Taybi syndrome

The purpose of this report is to describe the fluorescein angiography findings in a case of Rubinstein-Taybi syndrome. Fundus photography and fluorescein angiography were performed on a 6-year-old male with Rubinstein-Taybi syndrome due to CREB binding protein gene mutation. Fundus photography showed glaucomatous cupping and diffusely attenuated retinal vasculature. Choroidal vasculature was prominent due to diffuse retinal atrophy with scattered focal retinal pigment epithelial changes. Fluorescein angiography showed retinal vascular attenuation, prolonged arteriovenous transit time with delayed venous filling, late small vessel leakage, and 360 degrees of peripheral avascularity. Peripheral retinal avascularity and retinal vascular inflammation evidenced by late small vessel leakage can be demonstrated by fluorescein angiography in the retinal dystrophy of Rubinstein-Taybi syndrome.

Infantile glaucoma in Rubinstein-Taybi syndrome

PURPOSE

Long-term follow-up of patients with Rubinstein-Taybi-associated infantile glaucoma.

METHODS

Case series.

RESULTS

Three cases of infantile glaucoma in association with Rubinstein-Taybi syndrome are presented.

DISCUSSION

This report highlights the importance of measuring intraocular pressure in this condition, as glaucoma is one of the major preventable causes of blindness in childhood.

Evaluation of pediatric cataracts and systemic disorders

PURPOSE OF REVIEW

The purpose of this review is to outline those systemic disorders with associated cataracts to help in the evaluation and diagnosis of the patient with pediatric cataract who has systemic abnormalities.

RECENT FINDINGS

With the profound advancement in genetics, both making and confirming a diagnosis in rare syndromic disorders have become even more possible. By diagnosing a syndromic cataract, the patient and family members are afforded the opportunity to obtain a better understanding of their disorder as well as develop expectations as to the course of their child's disorder.

SUMMARY

The intent of this article is to act as a resource for helping to determine the cause of cataracts based on the lens appearance, age of onset and systemic findings. Children with cataracts, especially when bilateral, require a comprehensive history and ophthalmic examination with physician awareness toward other organ system involvement. A basic assessment of facial, skeletal, genitourinary, gastrointestinal and integumentary abnormalities is beneficial. In this review, there are numerous tables that are to act as a resource in developing a differential diagnosis and guide further systemic and genetic evaluation.

Adults with Rubinstein-Taybi syndrome

Information in the medical literature regarding adults with genetic syndromes is limited, making the care of these patients challenging. We conducted a questionnaire study of adults with Rubinstein-Taybi syndrome that addressed medical problems, education, independence, and behavior. The most common medical problems included short stature, obesity, visual difficulties, keloids, eating problems, spine curvature, and joint problems. The adults had typically moderate mental retardation, but most achieved some independence in self-care and communication; many participated in supported work situations. However, approximately one-third were said to have some decreased abilities over time. Behavior problems were common and often worsened with age. Very few of the study participants were seeing a geneticist as an adult. Long-term involvement of geneticists and education of adult primary care providers may help with many of the challenges facing adults with RTS and their families.

Two adults with Rubinstein-Taybi syndrome with mild mental retardation, glaucoma, normal growth and skull circumference, and camptodactyly of third fingers

The Rubinstein-Taybi syndrome (RTS; OMIM 180849) is a well-defined mental retardation/multiple congenital anomalies (MR/MCA) syndrome characterized by postnatal growth retardation, microcephaly, specific facial features, broad thumbs and halluces, and MR of variable degree. Ten percent of patients with RTS have a microdeletion 16p13.3, 40-50% carry a mutation of the CREBBP gene and another 3% have a mutation in the EP300 gene. In the remaining patients with clinically suspected RTS no mutation can be detected. Here we describe two patients with an RTS phenotype, one with a mutation in the CREBBP gene and the other without a detectable CREBBP or EP300 mutation and without a chromosomal imbalance on high-resolution arrays. Both patients present with the characteristic facial RTS phenotype, broad thumbs and big toes, mild MR, formation of keloids and glaucoma, but without postnatal growth retardation or microcephaly. In addition, they have both congenital camptodactyly of third (and fourth) fingers, which has not reported in RTS previously. We suggest that they represent a clinical subtype of RTS.

Chromosomal Abnormalities and Glaucoma: A Case of Congenital Glaucoma with Trisomy 8q22-Qter/ Monosomy 9p23-Pter

PURPOSE

To present a case of congenital glaucoma with an unbalanced translocation trisomy 8q22-qter/monosomy 9p23-pter, resulting in trisomy of the GLC1D locus. To perform a literature review of chromosomal abnormalities associated with glaucoma.

METHOD

A case report of a family with balanced translocation without glaucoma and unbalanced translocation with congenital glaucoma. PubMed and OMIM databases were searched for reports of chromosomal abnormalities and glaucoma.

RESULTS

Other case reports of congenital glaucoma with chromosomal abnormalities in this region were identified. A review of cytogenetics in southeastern Australia found nine cases involving the loss of 9p23 and 10 cases involving mosaicism for trisomy 8, but none had congenital glaucoma. A review of the literature identified reports of glaucoma and chromosomal abnormalities in regions with glaucoma loci mapped by conventional linkage analysis. These include the loci GLC1B, GLC1C, GLC1D, GLC1F, GPDS1, and RIEG2.

CONCLUSION

The study of patients with glaucoma and chromosomal abnormalities may help to identify new glaucoma genes. Ophthalmologists can assist with this by requesting cytogenetic studies on congenital and developmental glaucoma cases and interacting with ophthalmic genetics researchers.

Genetic and epigenetic mechanisms of gene regulation during lens development

Recent studies demonstrated a number of links between chromatin structure, gene expression, extracellular signaling and cellular differentiation during lens development. Lens progenitor cells originate from a pool of common progenitor cells, the pre-placodal region (PPR) which is formed from a combination of extracellular signaling between the neural plate, naïve ectoderm and mesendoderm. A specific commitment to the lens program over alternate choices such as the formation of olfactory epithelium or the anterior pituitary is manifested by the formation of a thickened surface ectoderm, the lens placode. Mouse lens progenitor cells are characterized by the expression of a complement of lens lineage-specific transcription factors including Pax6, Six3 and Sox2, controlled by FGF and BMP signaling, followed later by c-Maf, Mab21like1, Prox1 and FoxE3. Proliferation of lens progenitors together with their morphogenetic movements results in the formation of the lens vesicle. This transient structure, comprised of lens precursor cells, is polarized with its anterior cells retaining their epithelial morphology and proliferative capacity, whereas the posterior lens precursor cells initiate terminal differentiation forming the primary lens fibers. Lens differentiation is marked by expression and accumulation of crystallins and other structural proteins. The transcriptional control of crystallin genes is characterized by the reiterative use of transcription factors required for the establishment of lens precursors in combination with more ubiquitously expressed factors (e.g. AP-1, AP-2alpha, CREB and USF) and recruitment of histone acetyltransferases (HATs) CBP and p300, and chromatin remodeling complexes SWI/SNF and ISWI. These studies have poised the study of lens development at the forefront of efforts to understand the connections between development, cell signaling, gene transcription and chromatin remodeling.

Distinct embryonic expression and localization of CBP and p300 histone acetyltransferases at the mouse alphaA-crystallin locus in lens

Mouse alphaA-crystallin gene encodes the most abundant protein of the mammalian lens. Expression of alphaA-crystallin is regulated temporally and spatially during lens development with initial expression in the lens vesicle followed by strong upregulation in the differentiating primary lens fibers. Lens-specific expression of alphaA-crystallin is mediated by DNA-binding transcription factors Pax6, c-Maf and CREB bound to its promoter region. Its 5'-distal enhancer, DCR1, mediates regulation of alphaA-crystallin via FGF signaling, while its 3'-distal enhancer, DCR3, functions only in elongated primary lens fibers via other lens differentiation pathways. DCR1 and DCR3 establish outside borders of a lens-specific chromatin region marked by histone H3 K9 acetylation. Here, we identified CREB-binding protein (CBP) and p300 as major histone acetyltransferases (HATs) associated in vivo with the mouse alphaA-crystallin locus. Both HATs are expressed in embryonic lens. Expression of CBP in primary lens fiber cells coincides with alphaA-crystallin. In the chromatin of lens epithelial cells, chromatin immunoprecipitations (ChIPs) show that the alphaA-crystallin promoter is notably devoid of any significant presence of CBP and p300, though DCR1 and a few other regions show the presence of these HATs. In the chromatin obtained from newborn lens, CBP was localized specifically at the promoter region with about ten times higher abundance compared to the entire alphaA-crystallin locus. In contrast, p300 is distributed more evenly across the entire locus. Analysis of total histone H3 and H3 K9 acetylation revealed potential lower density of nucleosomes 2 kb upstream from the promoter region. Collectively, our data suggest that moderate level of alphaA-crystallin gene expression in lens epithelial cells does not require the presence of CBP and p300 in the promoter. However, the lens-specific chromatin domain contains both promoter localized CBP on the "background" of locus-spread presence of CBP and p300.