POLR1B and neural crest cell anomalies in Treacher Collins syndrome type 4

Possible germline mosaicism in a pedigree with Treacher Collins syndrome: A case report and brief review

Treacher Collins syndrome (TCS) is a rare congenital craniofacial disorder, typically inherited as an autosomal dominant condition. Here, we report on a family in which germline mosaicism for TCS was likely present. The proband was diagnosed with TCS based on the typical clinical features and a pathogenic variant TCOF1 (c.4369_4373delAAGAA, p.K1457Efs*12). The mutation was not detected in his parents' peripheral blood DNA samples, suggesting a de novo mutation had occurred in the proband. However, a year later, the proband's mother became pregnant, and the amniotic fluid puncture revealed that the fetus carried the same mutation as the proband. Prenatal ultrasound also indicated a maxillofacial dysplasia with unilateral microtia. The mother then disclosed a previous birth history in which a baby had died of respiratory distress shortly after birth, displaying a TCS-like phenotype. Around the same time, the proband's father was diagnosed with mild bilateral conductive hearing loss. Based on array data, we concluded that the father may have had germline mosaicism for TCOF1 mutation. Our findings highlight the importance of considering germline mosaicism in sporadic de novo TCOF1 mutations when providing genetic consulting, and prenatal diagnosis is important when the proband's parents become pregnant again.

A novel intronic TCOF1 pathogenic variant in a Chinese family with Treacher Collins syndrome

BACKGROUND

Treacher Collins syndrome (TCS; OMIM 154500) is a craniofacial developmental disorder.

METHODS

To investigate the genetic features of a four-generation Chinese family with TCS, clinical examinations, hearing tests, computed tomography, whole-exome sequencing (WES), Sanger sequencing, reverse transcription (RT)-PCR, and the Minigene assay were performed.

RESULTS

The probands, an 11-year-old male and his cousin exhibited typical clinical manifestations of TCS including conductive hearing loss, downward slanting palpebral fissures, and mandibular hypoplasia. Computed tomography revealed bilateral fusion of the anterior and posterior stapedial crura and malformation of the long crura of the incus. WES of both patients revealed a novel heterozygous intronic variant, i.e., c.4342 + 5_4342 + 8delGTGA (NM_001371623.1) in TCOF1. Minigene expression analysis revealed that the c.4342 + 5_4342 + 8delGTGA variant in TCOF1 caused a partial deletion of exon 24 (c.4115_4342del: p.Gly1373_Arg1448del), which was predicted to yield a truncated protein. The deletion was further confirmed via RT-PCR and sequencing of DNA from proband blood cells. A heterozygous variant in the POLR1C gene (NM_203290; exon6; c.525delG) was found almost co-segregated with the TCOF1 pathogenic variant.

CONCLUSIONS

In conclusion, we identified a heterozygous TCOF1 splicing variant c.4342 + 5_4342 + 8delGTGA (splicing) in a Chinese TSC family with ossicular chain malformations and facial anomalies. Our findings broadened the spectrum of TCS variants and will facilitate diagnostics and prognostic predictions.

Diamond-Blackfan anemia, the archetype of ribosomopathy: How distinct is it from the other constitutional ribosomopathies?

Diamond-Blackfan anemia (DBA) was the first ribosomopathy described in humans. DBA is a congenital hypoplastic anemia, characterized by macrocytic aregenerative anemia, manifesting by differentiation blockage between the BFU-e/CFU-e developmental erythroid progenitor stages. In 50 % of the DBA cases, various malformations are noted. Strikingly, for a hematological disease with a relative erythroid tropism, DBA is due to ribosomal haploinsufficiency in 24 different ribosomal protein (RP) genes. A few other genes have been described in DBA-like disorders, but they do not fit into the classical DBA phenotype (Sankaran et al., 2012; van Dooijeweert et al., 2022; Toki et al., 2018; Kim et al., 2017 [1-4]). Haploinsufficiency in a RP gene leads to defective ribosomal RNA (rRNA) maturation, which is a hallmark of DBA. However, the mechanistic understandings of the erythroid tropism defect in DBA are still to be fully defined. Erythroid defect in DBA has been recently been linked in a non-exclusive manner to a number of mechanisms that include: 1) a defect in translation, in particular for the GATA1 erythroid gene; 2) a deficit of HSP70, the GATA1 chaperone, and 3) free heme toxicity. In addition, p53 activation in response to ribosomal stress is involved in DBA pathophysiology. The DBA phenotype may thus result from the combined contributions of various actors, which may explain the heterogenous phenotypes observed in DBA patients, even within the same family.

Genetics and Epigenetics in the Genesis and Development of Microtia

Microtia is a congenital malformation of the external and middle ear associated with varying degrees of severity that range from mild structural abnormalities to the absence of the external ear and auditory canal. Globally, it is the second most common congenital craniofacial malformation and is typically caused by inherited defects, external factors, or the interaction between genes and external factors. Epigenetics notably represents a bridge between genetics and the environment. This review has devoted attention to the current proceedings of the genetics and epigenetics of microtia and related syndromes.

A Novel Missense Variant in the TCOF1 Gene in one Chinese Case With Treacher Collins Syndrome

The purpose of this study is to analyze the clinical characteristics of a Treacher Collins syndrome (TCS) patient carrying a de novo variant of TCOF1, and briefly analyze the correlation between genetic results and clinical features. Also, the pathogenesis and clinical treatment of TCS are reviewed.

A Chinese pedigree with TCS containing 8 members was enrolled. Phenotype of the proband was evaluated by a surgeon, then whole exome sequencing of the proband was performed. Then we verified the proband-derived variants by Sanger sequencing in the pedigree. Correlation between genotype and phenotype was analyzed.

The study was conducted in a stomatological hospital.

A Chinese pedigree with TCS containing 8 members.

To ascertain the genetic variants in the Chinese pedigree with TCS.

Blood samples were collected.

We reported a case of typical TCS with a de novo missense variant (NM_001371623.1:c.38T>G, p.(Leu13Arg)) in exon 1 of TCOF1, who presented asymmetrical facial abnormalities, including downward slanting of the palpebral fissures, sparse eyebrows, lateral tilt of the eyeballs, bilateral external ears deformities, hypoplasia of midface, reduction of the zygomatic body, bilateral orbital invagination, right external auditory canal atresia, mandibular ramus short deformity, cleft palate and the whole face was convex.

This research found a novel variant of TCS in Chinese, expanding the spectrum of TCS pathogenic variants. Genetic results combined with clinical phenotype can make a definite diagnosis and provide genetic counseling for the family.

Conductive Hearing Loss in Children

A variety of congenital and acquired disorders result in pediatric conductive hearing loss. Malformations of the external auditory canal are invariably associated with malformations of the middle ear space and ossicles. Isolated ossicular malformations are uncommon. Syndromes associated with external and middle ear malformations are frequently associated with abnormal development of first and second pharyngeal arch derivatives. Chronic inflammatory disorders include cholesteatoma, cholesterol granuloma, and tympanosclerosis.

Synthesis of the ribosomal RNA precursor in human cells: mechanisms, factors and regulation

The ribosomal RNA precursor (pre-rRNA) comprises three of the four ribosomal RNAs and is synthesized by RNA polymerase (Pol) I. Here, we describe the mechanisms of Pol I transcription in human cells with a focus on recent insights gained from structure-function analyses. The comparison of Pol I-specific structural and functional features with those of other Pols and with the excessively studied yeast system distinguishes organism-specific from general traits. We explain the organization of the genomic rDNA loci in human cells, describe the Pol I transcription cycle regarding structural changes in the enzyme and the roles of human Pol I subunits, and depict human rDNA transcription factors and their function on a mechanistic level. We disentangle information gained by direct investigation from what had apparently been deduced from studies of the yeast enzymes. Finally, we provide information about how Pol I mutations may contribute to developmental diseases, and why Pol I is a target for new cancer treatment strategies, since increased rRNA synthesis was correlated with rapidly expanding cell populations.

[TCOF1 Gene variation in Treacher Collins syndrome and evaluation of speech rehabilitation after bone bridge surgery]

Objective:By analyzing the clinical phenotypic characteristics and gene sequences of two patients with Treacher Collins syndrome（TCS）, the biological causes of the disease were determined. Then discuss the therapeutic effect of hearing intervention after bone bridge implantation. Methods:All clinical data of the two family members were collected, and the patients signed the informed consent. The peripheral blood of the proband and family members was extracted, DNA was extracted for whole exome sequencing, and Sanger sequencing was performed on the family members for the mutation site.TCOF1genetic mutations analysis was performed on the paitents. Then, the hearing threshold and speech recognition rate of family 2 proband were evaluated and compared under the sound field between bare ear and wearing bone bridge. Results:In the two pedigrees, the probands of both families presented with auricle deformity, zygomatic and mandibular hypoplasia, micrognathia, hypotropia of the eye fissure, and hypoplasia of the medial eyelashes. The proband of Family 1 also presents with specific features including right-sided narrow anterior nasal aperture and dental hypoplasia, which were consistent with the clinical diagnosis of Treacher Collins syndrome. Genetic testing was conducted on both families, and two heterozygous mutations were identified in the TCOF1 gene: c. 1350_1351dupGG（p. A451Gfs*43） and c. 4362_4366del（p. K1457Efs*12）, resulting in frameshift mutations in the amino acid sequence. Sanger sequencing validation of the TCOF1 gene in the parents of the proband in Family 1 did not detect any mutations. Proband 1 TCOF1 c. 1350_1351dupGG heterozygous variants have not been reported previously. The postoperative monosyllabic speech recognition rate of family 2 proband was 76%, the Categories of Auditory Performance（CAP） score was 6, and the Speech Intelligibility Rating（SIR） score was 4. Assessment using the Meaningful Auditory Integration Scale（MAIS） showed notable improvement in the patient's auditory perception, comprehension, and usage of hearing aids. Evaluation using the Glasgow Children's Benefit Inventory and quality of life assessment revealed significant improvements in the child's self care abilities, daily living and learning, social interactions, and psychological well being, as perceived by the parents. Conclusion:This study has elucidated the biological cause of Treacher Collins syndrome, enriched the spectrum of TCOF1 gene mutations in the Chinese population, and demonstrated that bone bridge implantation can improve the auditory and speech recognition rates in TCS patients.

HMG-boxes, ribosomopathies and neurodegenerative disease

The UBTF E210K neuroregression syndrome is a predominantly neurological disorder caused by recurrent de novo dominant variants in Upstream Binding Factor, that is, essential for transcription of the ribosomal RNA genes. This unusual form of ribosomopathy is characterized by a slow decline in cognition, behavior, and sensorimotor functioning during the critical period of development. UBTF (or UBF) is a multi-HMGB-box protein that acts both as an epigenetic factor to establish "open" chromatin on the ribosomal genes and as a basal transcription factor in their RNA Polymerase I transcription. Here we review the possible mechanistic connections between the UBTF variants, ribosomal RNA gene transcription and the neuroregression syndrome, and suggest that DNA topology may play an important role.

rRNA transcription is integral to phase separation and maintenance of nucleolar structure

Transcription of ribosomal RNA (rRNA) by RNA Polymerase (Pol) I in the nucleolus is necessary for ribosome biogenesis, which is intimately tied to cell growth and proliferation. Perturbation of ribosome biogenesis results in tissue specific disorders termed ribosomopathies in association with alterations in nucleolar structure. However, how rRNA transcription and ribosome biogenesis regulate nucleolar structure during normal development and in the pathogenesis of disease remains poorly understood. Here we show that homozygous null mutations in Pol I subunits required for rRNA transcription and ribosome biogenesis lead to preimplantation lethality. Moreover, we discovered that Polr1a-/-, Polr1b-/-, Polr1c-/- and Polr1d-/- mutants exhibit defects in the structure of their nucleoli, as evidenced by a decrease in number of nucleolar precursor bodies and a concomitant increase in nucleolar volume, which results in a single condensed nucleolus. Pharmacological inhibition of Pol I in preimplantation and midgestation embryos, as well as in hiPSCs, similarly results in a single condensed nucleolus or fragmented nucleoli. We find that when Pol I function and rRNA transcription is inhibited, the viscosity of the granular compartment of the nucleolus increases, which disrupts its phase separation properties, leading to a single condensed nucleolus. However, if a cell progresses through mitosis, the absence of rRNA transcription prevents reassembly of the nucleolus and manifests as fragmented nucleoli. Taken together, our data suggests that Pol I function and rRNA transcription are required for maintaining nucleolar structure and integrity during development and in the pathogenesis of disease.

POLR1A variants underlie phenotypic heterogeneity in craniofacial, neural, and cardiac anomalies

Heterozygous pathogenic variants in POLR1A, which encodes the largest subunit of RNA Polymerase I, were previously identified as the cause of acrofacial dysostosis, Cincinnati-type. The predominant phenotypes observed in the cohort of 3 individuals were craniofacial anomalies reminiscent of Treacher Collins syndrome. We subsequently identified 17 additional individuals with 12 unique heterozygous variants in POLR1A and observed numerous additional phenotypes including neurodevelopmental abnormalities and structural cardiac defects, in combination with highly prevalent craniofacial anomalies and variable limb defects. To understand the pathogenesis of this pleiotropy, we modeled an allelic series of POLR1A variants in vitro and in vivo. In vitro assessments demonstrate variable effects of individual pathogenic variants on ribosomal RNA synthesis and nucleolar morphology, which supports the possibility of variant-specific phenotypic effects in affected individuals. To further explore variant-specific effects in vivo, we used CRISPR-Cas9 gene editing to recapitulate two human variants in mice. Additionally, spatiotemporal requirements for Polr1a in developmental lineages contributing to congenital anomalies in affected individuals were examined via conditional mutagenesis in neural crest cells (face and heart), the second heart field (cardiac outflow tract and right ventricle), and forebrain precursors in mice. Consistent with its ubiquitous role in the essential function of ribosome biogenesis, we observed that loss of Polr1a in any of these lineages causes cell-autonomous apoptosis resulting in embryonic malformations. Altogether, our work greatly expands the phenotype of human POLR1A-related disorders and demonstrates variant-specific effects that provide insights into the underlying pathogenesis of ribosomopathies.

A biallelic variant in POLR2C is associated with congenital hearing loss and male infertility: Case report

BACKGROUND

DNA-directed RNA polymerase II subunit 3 (RPB3) is the third largest subunit of RNA polymerase II and is encoded by the POLR2C (OMIM:180663). A large Iranian family with congenital hearing loss and infertility is described here with genetic and clinical characterizations of five male patients.

METHODS

After doing clinical examinations, the proband was subjected to karyotyping and GJB2/6 sequencing to rule out the most evident chromosomal and gene abnormalities for male infertility and hearing loss, respectively. A custom-designed next-generation sequencing panel was also used to detect mutations in deafness-related genes. Finally, to reveal the underlying molecular cause(s) justifying hearing loss and male infertility, five male patients and 2 healthy male controls within the family were subjected to paired-end whole-exome sequencing (WES). Linkage analysis was also performed based on the data.

RESULTS

All male patients showed prelingual sensorineural hearing loss and also decreased sperm motility. Linkage analysis determined 16q21 as the most susceptible locus in which a missense variant in exon 7 of POLR2C-NM_032940.3:c.545T>C;p.(Val182Ala)-was identified as a 'likely pathogenic' variant co-segregated with phenotypes.

CONCLUSIONS

Using segregation and in silico analyses, for the first time, we suggested that the NM_032940.3:c.545T>C; p.(Val182Ala) in POLR2C is associated with hearing loss and male infertility.

Molecular etiology of defective nuclear and mitochondrial ribosome biogenesis: Clinical phenotypes and therapy

Ribosomopathies are rare congenital disorders associated with defective ribosome biogenesis due to pathogenic variations in genes that encode proteins related to ribosome function and biogenesis. Defects in ribosome biogenesis result in a nucleolar stress response involving the TP53 tumor suppressor protein and impaired protein synthesis leading to a deregulated translational output. Despite the accepted notion that ribosomes are omnipresent and essential for all cells, most ribosomopathies show tissue-specific phenotypes affecting blood cells, hair, spleen, or skin. On the other hand, defects in mitochondrial ribosome biogenesis are associated with a range of clinical manifestations affecting more than one organ. Intriguingly, the deregulated ribosomal function is also a feature in several human malignancies with a selective upregulation or downregulation of specific ribosome components. Here, we highlight the clinical conditions associated with defective ribosome biogenesis in the nucleus and mitochondria with a description of the affected genes and the implicated pathways, along with a note on the treatment strategies currently available for these disorders.

Nucleolar stress: From development to cancer

The nucleolus is a large nuclear membraneless organelle responsible for ribosome biogenesis. Ribosomes are cytoplasmic macromolecular complexes comprising RNA and proteins that link amino acids together to form new proteins. The biogenesis of ribosomes is an intricate multistep process that involves the transcription of ribosomal DNA (rDNA), the processing of ribosomal RNA (rRNA), and the assembly of rRNA with ribosomal proteins to form active ribosomes. Nearly all steps necessary for ribosome production and maturation occur in the nucleolus. Nucleolar shape, size, and number are directly linked to ribosome biogenesis. Errors in the steps of ribosomal biogenesis are sensed by the nucleolus causing global alterations in nucleolar function and morphology. This phenomenon, known as nucleolar stress, can lead to molecular changes such as stabilization of p53, which in turn activates cell cycle arrest or apoptosis. In this review, we discuss recent work on the association of nucleolar stress with degenerative diseases and developmental defects. In addition, we highlight the importance of de novo nucleotide biosynthesis for the enhanced nucleolar activity of cancer cells and discuss targeting nucleotide biosynthesis as a strategy to activate nucleolar stress to specifically target cancer cells.

RNA Polymerases I and III in development and disease

Ribosomes are macromolecular machines that are globally required for the translation of all proteins in all cells. Ribosome biogenesis, which is essential for cell growth, proliferation and survival, commences with transcription of a variety of RNAs by RNA Polymerases I and III. RNA Polymerase I (Pol I) transcribes ribosomal RNA (rRNA), while RNA Polymerase III (Pol III) transcribes 5S ribosomal RNA and transfer RNAs (tRNA) in addition to a wide variety of small non-coding RNAs. Interestingly, despite their global importance, disruptions in Pol I and Pol III function result in tissue-specific developmental disorders, with craniofacial anomalies and leukodystrophy/neurodegenerative disease being among the most prevalent. Furthermore, pathogenic variants in genes encoding subunits shared between Pol I and Pol III give rise to distinct syndromes depending on whether Pol I or Pol III function is disrupted. In this review, we discuss the global roles of Pol I and III transcription, the consequences of disruptions in Pol I and III transcription, disorders arising from pathogenic variants in Pol I and Pol III subunits, and mechanisms underpinning their tissue-specific phenotypes.

Regulation of ribosomal RNA gene copy number, transcription and nucleolus organization in eukaryotes

One of the first biological machineries to be created seems to have been the ribosome. Since then, organisms have dedicated great efforts to optimize this apparatus. The ribosomal RNA (rRNA) contained within ribosomes is crucial for protein synthesis and maintenance of cellular function in all known organisms. In eukaryotic cells, rRNA is produced from ribosomal DNA clusters of tandem rRNA genes, whose organization in the nucleolus, maintenance and transcription are strictly regulated to satisfy the substantial demand for rRNA required for ribosome biogenesis. Recent studies have elucidated mechanisms underlying the integrity of ribosomal DNA and regulation of its transcription, including epigenetic mechanisms and a unique recombination and copy-number control system to stably maintain high rRNA gene copy number. In this Review, we disucss how the crucial maintenance of rRNA gene copy number through control of gene amplification and of rRNA production by RNA polymerase I are orchestrated. We also discuss how liquid-liquid phase separation controls the architecture and function of the nucleolus and the relationship between rRNA production, cell senescence and disease.

A systematic review on Treacher Collins syndrome: Correlation between molecular genetic findings and clinical severity

Treacher Collins syndrome (TCS, OMIM: 154500) is a rare congenital craniofacial disorder that is caused by variants in the genes TCOF1, POLR1D, POLR1C, and POLR1B. Studies on the association between phenotypic variability and their relative variants are very limited. This systematic review summarized the 53 literatures from PubMed and Scopus to explore the potential TCS genotype-phenotype correlations with statistical analysis. Studies reporting both complete molecular genetics and clinical data were included. We identified that the molecular anomaly within TCOF1 (88.71%) accounted for most TCS cases. The only true hot spot for TCOF1 was detected in exon 24, with recurrent c.4369_4373delAAGAA variant is identified. While the hot spot for POLR1D, POLR1C, and POLR1B were identified in exons 3, 8, and 15, respectively. Our result suggested that the higher severity level was likely to be observed in Asian patients harboring TCOF1 variants rather than POLR1. Moreover, common 5-bp deletions tended to have a higher severity degree in comparison to any variants within exon 24 of TCOF1. In summary, this report suggested the relationship between genetic and clinical data in TCS. Our findings could be used as a reference for clinical diagnosis and further biological studies.

The human RNA polymerase I structure reveals an HMG-like docking domain specific to metazoans

We characterize the human RNA polymerase I by evolutionary biochemistry and cryo-EM revealing a built-in structural domain that apparently serves as transcription factor–binding platform in metazoans.

Transcription of the ribosomal RNA precursor by RNA polymerase (Pol) I is a major determinant of cellular growth, and dysregulation is observed in many cancer types. Here, we present the purification of human Pol I from cells carrying a genomic GFP fusion on the largest subunit allowing the structural and functional analysis of the enzyme across species. In contrast to yeast, human Pol I carries a single-subunit stalk, and in vitro transcription indicates a reduced proofreading activity. Determination of the human Pol I cryo-EM reconstruction in a close-to-native state rationalizes the effects of disease-associated mutations and uncovers an additional domain that is built into the sequence of Pol I subunit RPA1. This “dock II” domain resembles a truncated HMG box incapable of DNA binding which may serve as a downstream transcription factor–binding platform in metazoans. Biochemical analysis, in situ modelling, and ChIP data indicate that Topoisomerase 2a can be recruited to Pol I via the domain and cooperates with the HMG box domain–containing factor UBF. These adaptations of the metazoan Pol I transcription system may allow efficient release of positive DNA supercoils accumulating downstream of the transcription bubble.

Landscape of RNA-binding proteins in diagnostic utility, immune cell infiltration and PANoptosis features of heart failure

Objective: Heart failure remains a global public health problem linked to rising morbidity and mortality. RNA-binding proteins (RBPs) are crucial regulators in post-transcriptionally determining gene expression. Our study aimed to comprehensively elucidate the diagnostic utility and biological roles of RBPs in heart failure.

Methods: Genomic data of human failing and nonfailing left ventricular myocardium specimens were retrieved from the GEO datasets. Heart failure-specific RBPs were screened with differential expression analyses, and RBP-based subtypes were clustered with consensus clustering approach. GSEA was implemented for comparing KEGG pathways across subtypes. RBP-based subtype-related genes were screened with WGCNA. Afterwards, characteristic genes were selected through integrating LASSO and SVM-RFE approaches. A nomogram based on characteristic genes was established and verified through calibration curve, decision curve and clinical impact curve analyses. The abundance of immune cell types was estimated with CIBERSORT approach.

Results: Heart failure-specific RBPs were determined, which were remarkably linked to RNA metabolism process. Three RBP-based subtypes (namely C1, C2, C3) were established, characterized by distinct pathway activities and PANoptosis gene levels. C2 subtype presented the highest abundance of immune cells, followed by C1 and C3. Afterwards, ten characteristic genes were selected, which enabled to reliably diagnose heart failure risk. The characteristic gene-based nomogram enabled to accurately predict risk of heart failure, with the excellent clinical utility. Additionally, characteristic genes correlated to immune cell infiltration and PANoptosis genes.

Conclusion: Our findings comprehensively described the roles of RBPs in heart failure. Further research is required for verifying the effectiveness of RBP-based subtypes and characteristic genes in heart failure.

Dynamic regulation and requirement for ribosomal RNA transcription during mammalian development

Ribosomal RNA (rRNA) transcription by RNA polymerase I (Pol I) is a critical rate-limiting step in ribosome biogenesis, which is essential for cell survival. Despite its global function, disruptions in ribosome biogenesis cause tissue-specific birth defects called ribosomopathies, which frequently affect craniofacial development. Here, we describe a cellular and molecular mechanism underlying the susceptibility of craniofacial development to disruptions in Pol I transcription. We show that Pol I subunits are highly expressed in the neuroepithelium and neural crest cells (NCCs), which generate most of the craniofacial skeleton. High expression of Pol I subunits sustains elevated rRNA transcription in NCC progenitors, which supports their high tissue-specific levels of protein translation, but also makes NCCs particularly sensitive to rRNA synthesis defects. Consistent with this model, NCC-specific deletion of Pol I subunits Polr1a, Polr1c, and associated factor Tcof1 in mice cell-autonomously diminishes rRNA synthesis, which leads to p53 protein accumulation, resulting in NCC apoptosis and craniofacial anomalies. Furthermore, compound mutations in Pol I subunits and associated factors specifically exacerbate the craniofacial anomalies characteristic of the ribosomopathies Treacher Collins syndrome and Acrofacial Dysostosis-Cincinnati type. Mechanistically, we demonstrate that diminished rRNA synthesis causes an imbalance between rRNA and ribosomal proteins. This leads to increased binding of ribosomal proteins Rpl5 and Rpl11 to Mdm2 and concomitantly diminished binding between Mdm2 and p53. Altogether, our results demonstrate a dynamic spatiotemporal requirement for rRNA transcription during mammalian cranial NCC development and corresponding tissue-specific threshold sensitivities to disruptions in rRNA transcription in the pathogenesis of congenital craniofacial disorders.

DHX37 and 46,XY DSD: A New Ribosomopathy?

Recently, a series of recurrent missense variants in the RNA-helicase DHX37 have been reported associated with either 46,XY gonadal dysgenesis, 46,XY testicular regression syndrome (TRS), or anorchia. All affected children have non-syndromic forms of disorders/differences of sex development (DSD). These variants, which involve highly conserved amino acids within known functional domains of the protein, are predicted by in silico tools to have a deleterious effect on helicase function. DHX37 is required for ribosome biogenesis in eukaryotes, and how these variants cause DSD is unclear. The relationship between DHX37 and human congenital disorders is complex as compound heterozygous as well as de novo heterozygous missense variants in DHX37 are also associated with a complex congenital developmental syndrome (NEDBAVC, neurodevelopmental disorder with brain anomalies and with or without vertebral or cardiac anomalies; OMIM 618731), consisting of microcephaly, global developmental delay, seizures, facial dysmorphia, and kidney and cardiac anomalies. Here, we will give a brief overview of ribosome biogenesis and the role of DHX37 in this process. We will discuss variants in DHX37, their contribution to human disease in the general context of human ribosomopathies, and the possible disease mechanisms that may be involved.

[Genetic characteristics of microtia-associated syndromes in neonates]

Microtia is the second most common maxillofacial birth defect in neonates and has an prevalence rate of 3.06/10 000 in China, and 20%-60% of microtia cases is associated with a certain type of syndrome. This article elaborates on the clinical phenotypes and genetic characteristics of three microtia-associated syndromes (MASs) with high prevalence, high incidence rate of ear deformity, and definite genetic etiology, i.e., oculo-auriculo-vertebral spectrum, branchio-oto-renal spectrum disorder, and Treacher-Collins syndrome, and summarizes another three common MASs, so as to provide a reference for the genetic diagnosis of neonatal MAS.

Generation and characterization of a temperature-sensitive mutant allele of the second largest subunit of RNA polymerase I in Schizosaccharomyces pombe

RNA polymerase I (Pol I) is a highly conserved complex that catalyzes the transcription of rRNA precursors in the nucleolus. In this study, we isolated a temperature-sensitive (ts) allele of Rpa2, the second largest subunit of Pol I in the fission yeast Schizosaccharomyces pombe . We found that rpa2 ^ts cells were severely defective in growth at temperatures above 32 °C. We also found that rpa2 ^ts cells showed aberrant chromosome segregation and an abnormal ring-like nuclear structure at the restrictive temperature. These findings suggest that Rpa2 is essential for faithful nuclear division and nuclear structural organization in S. pombe .

Treacle Sticks the Nucleolar Responses to DNA Damage Together

The importance of chromatin environment for DNA repair has gained increasing recognition in recent years. The nucleolus is the largest sub-compartment within the nucleus: it has distinct biophysical properties, selective protein retention, and houses the specialized ribosomal RNA genes (collectively referred to as rDNA) with a unique chromatin composition. These genes have high transcriptional activity and a repetitive nature, making them susceptible to DNA damage and resulting in the highest frequency of rearrangements across the genome. A distinct DNA damage response (DDR) secures the fidelity of this genomic region, the so-called nucleolar DDR (n-DDR). The composition of the n-DDR reflects the characteristics of nucleolar chromatin with the nucleolar protein Treacle (also referred to as TCOF1) as a central coordinator retaining several well-characterized DDR proteins in the nucleolus. In this review, we bring together data on the structure of Treacle, its known functions in ribosome biogenesis, and its involvement in multiple branches of the n-DDR to discuss their interconnection. Furthermore, we discuss how the functions of Treacle in ribosome biogenesis and in the n-DDR may contribute to Treacher Collins Syndrome, a disease caused by mutations in Treacle. Finally, we outline outstanding questions that need to be addressed for a more comprehensive understanding of Treacle, the n-DDR, and the coordination of ribosome biogenesis and DNA repair.

Exome and RNA-Seq analyses of an incomplete penetrance variant in USP9X in female-specific syndromic intellectual disability

Pathogenic variants in USP9X, on X chromosome, have been implicated in syndromic intellectual disability (ID) in both males and females with distinct craniofacial features. We report a truncating variant, c.885_889delAAAAG, p.(Lys296Serfs*4), in the USP9X gene with incomplete penetrance in two nontwin female siblings with phenotypic resemblance to female-specific syndromic ID (MIM 300969, also known as MRX99F). To investigate the possible genetic etiology of the reduced penetrance, X-inactivation, RNA-Seq, and full quad exome analyses were attempted, but failed to identify a promising candidate modifier. While the penetrance of pathogenic variants in USP9X in female appears to be high (95%) and the variants frequently occur de novo, incomplete penetrance should be considered.

Regulation of Nucleolar Activity by MYC

The nucleolus harbors the machinery necessary to produce new ribosomes which are critical for protein synthesis. Nucleolar size, shape, and density are highly dynamic and can be adjusted to accommodate ribosome biogenesis according to the needs for protein synthesis. In cancer, cells undergo continuous proliferation; therefore, nucleolar activity is elevated due to their high demand for protein synthesis. The transcription factor and universal oncogene MYC promotes nucleolar activity by enhancing the transcription of ribosomal DNA (rDNA) and ribosomal proteins. This review summarizes the importance of nucleolar activity in mammalian cells, MYC’s role in nucleolar regulation in cancer, and discusses how a better understanding (and the potential inhibition) of aberrant nucleolar activity in cancer cells could lead to novel therapeutics.

Metal transporter Slc30a1 controls pharyngeal neural crest differentiation via the zinc-Snai2-Jag1 cascade

The pharyngeal arch (PA) is a neural crest (NC)-derived organ that is transiently developed during embryogenesis and is required for the subsequent development of various tissues. However, the role of zinc during PA differentiation from NC progenitor cells is unknown. Here, we found that the metal transporters Slc30a1a and Slc30a1b mediate zinc homeostasis during PA differentiation. Slc30a1-deficient zebrafish develop zinc accumulation in NC cells, with increased expression of stemness markers and PA dorsal genes, and SMART-seq analyses revealed that the genes snai2 and jag1b may serve as downstream targets. Furthermore, functional studies showed that knocking down either snai2 or jag1b rescues PA development in Slc30a1-deficient zebrafish. Notably, we identified the double zinc-finger domain in the transcription factor Snai2 as a zinc-responsive element that regulates jag1b expression. Our findings indicate that the Slc30a1/zinc-snai2-jag1b axis is an essential regulatory network controlling PA differentiation, shedding new light on the function of zinc homeostasis in maintaining NC cell stemness and multipotency in vertebrates.

Genetics of craniofacial malformations

The field of craniofacial malformations is comprehensive and does not allow to discuss all craniofacial malformations which have been described as single entities. Many of the syndromes with craniofacial malformations are ultrarare. In this review we have chosen craniofacial malformation syndromes which are of relevance for the pediatrician, especially neonatologist: different types of craniosynostoses, oculo-auriculo-vertebral spectrum, Pierre Robin sequence and Treacher Collins syndrome. These syndromes will be described in detail. Diagnostic and therapeutic options will be discussed.

A homozygous missense variant in laminin subunit beta 1 as candidate causal mutation of hemifacial microsomia in Romagnola cattle

Hemifacial microsomia (HFM) was diagnosed in a 9‐day‐old Romagnola calf. The condition was characterized by microtia of the left ear, anotia of the right ear, asymmetry of the face, and deafness. Magnetic resonance imaging revealed agenesis of the right pinna and both tympanic bullae, asymmetry of the temporal bones and temporomandibular joints, and right pontine meningocele. Brainstem auditory evoked responses confirmed the impaired auditory capacity. At gross post mortem examination, there was agenesis and hypoplasia of the right and the left external ear, respectively. No histological abnormalities were detected in the inner ears. A trio whole‐genome sequencing approach was carried out and identified a private homozygous missense variant in LAMB1 affecting a conserved residue (p.Arg668Cys). Genotyping of 221 Romagnola bulls revealed a carrier prevalence <2%. This represents a report of a LAMB1‐related autosomal recessive inherited disorder in domestic animals and adds LAMB1 to the candidate genes for HFM.

N6-methyladenosine (m6A) modification of ribosomal RNAs (rRNAs): Critical roles in mRNA translation and diseases

As key components of the ribosome and the most abundant RNA species, the rRNAs are modified during ribosome formation. N⁶-methyladenosine (m⁶A) is a conserved RNA modification occurring on different RNA species including rRNAs. Recently, it has been reported that ZCCHC4 and METTL5 are methyltransferases that mediate m⁶A modification of human 28S and 18S rRNA, respectively. The newly discovered biological functions of the two methyltransferases include regulation of mRNA translation, cell proliferation, cell differentiation, stress response, and other biological processes. Both of them, especially METTL5, have been proved to be associated with a variety of diseases such as intellectual disability, cancer, congenital dysplasia and have potential clinical application as biomarkers and therapeutic targets.

Structure of the human RNA polymerase I elongation complex

Eukaryotic RNA polymerase I (Pol I) transcribes ribosomal DNA and generates RNA for ribosome synthesis. Pol I accounts for the majority of cellular transcription activity and dysregulation of Pol I transcription leads to cancers and ribosomopathies. Despite extensive structural studies of yeast Pol I, structure of human Pol I remains unsolved. Here we determined the structures of the human Pol I in the pre-translocation, post-translocation, and backtracked states at near-atomic resolution. The single-subunit peripheral stalk lacks contacts with the DNA-binding clamp and is more flexible than the two-subunit stalk in yeast Pol I. Compared to yeast Pol I, human Pol I possesses a more closed clamp, which makes more contacts with DNA. The Pol I structure in the post-cleavage backtracked state shows that the C-terminal zinc ribbon of RPA12 inserts into an open funnel and facilitates “dinucleotide cleavage” on mismatched DNA–RNA hybrid. Critical disease-associated mutations are mapped on Pol I regions that are involved in catalysis and complex organization. In summary, the structures provide new sights into human Pol I complex organization and efficient proofreading.

Three-dimensional comparison of mandibular morphology in young people with Treacher Collins syndrome and Pierre Robin sequence

INTRODUCTION

Treacher Collins syndrome (TCS) and nonsyndromic Pierre Robin sequence (PRS) share mandibular deficiency as a similar clinical finding. This study aimed to compare the mandibular size and morphology of subjects with TCS and PRS.

METHODS

Group TCS was composed of 17 subjects (7 male, 10 female) with a mean age of 11.5 years (standard deviation, 4.4) from a single center. Group PRS was composed of 17 subjects paired by age and sex with group TCS. Preorthodontic cone-beam computed tomography examinations of all patients were evaluated using Mimics Innovation Suite 17.0 (Materialise, Leuven, Belgium). Nine 3-dimensional measurements were performed in segmented 3D images of the mandible. Intragroup comparisons were performed using paired t tests. Intergroup comparisons were performed using analysis of variance and Tukey tests. The significance level considered was 5%.

RESULTS

TCS showed a significant dimensional difference between less and more affected sides for ramus, condyles, and mandibular body. The mandibular dimensions in PRS were more symmetrical. Group TCS presented a smaller mandibular effective length and mandibular body length compared with PRS. The condyle width and height and the ramus width were also decreased in TCS. The gonial angle was greater in TCS compared with the PRS group.

CONCLUSIONS

Young subjects with TCS presented a smaller, more vertical, and more asymmetrical mandible compared with nonsyndromic PRS.

Identification of three novel TCOF1 mutations in patients with Treacher Collins Syndrome

Here we describe three novel TCOF1 mutations found in unrelated patients with Treacher Collins syndrome. These mutations include one deletion, NM_001135243.2:c.2604_2605delAG (p.Gly869Glufs*3), and two substitutions, NM_001135243.2:c.2575C>T (p.Gln859*) and NM_001135243.2:c.4111G>T (p.Glu1371*). These mutations cause shortening of a protein called Treacle in patients with features typical of TCS. Continuous identification of new mutations is important to expand the mutation base, which is helpful in the diagnosis of both patients and their families

Treacher Collins Syndrome: Genetics, Clinical Features and Management

Treacher Collins syndrome (TCS) is associated with abnormal differentiation of the first and second pharyngeal arches, occurring during fetal development. Features of TCS include microtia with conductive hearing loss, slanting palpebral fissures with possibly coloboma of the lateral part of lower eyelids, midface hypoplasia, micrognathia as well as sporadically cleft palate and choanal atresia or stenosis. TCS occurs in the general population at a frequency of 1 in 50,000 live births. Four subtypes of Treacher Collins syndrome exist. TCS can be caused by pathogenic variants in the TCOF1, POLR1D, POLR1C and POLR1B genes. Genetically, the TCOF1 gene contains 27 exons which encodes the Treacle protein. In TCOF1, over 200 pathogenic variants have been identified, of which most are deletions leading to a frame-shift, that result in the formation of a termination codon. In the presented article, we review the genetics and phenotype of TCS as well as the management and surgical procedures utilized for treatment.

Phenotype Analysis and Genetic Study of Chinese Patients With Treacher Collins Syndrome

OBJECTIVE

The aim of this study was to confirm the pathogenic variants, explore the genotype-phenotype correlation and characteristics of Chinese patients with Treacher Collins syndrome (TCS).

DESIGN

Clinical details of 3 TCS family cases and 2 sporadic cases were collected and analyzed. Whole-exome sequencing and Sanger sequencing were conducted to detect causative variants.

SETTING

Tertiary clinical care.

PATIENTS

This study included 8 patients clinically diagnosed with TCS who were from 3 familial cases and 2 sporadic cases.

MAIN OUTCOME MEASURES

When filtering the database, variants were saved as rare variants if their frequency were less than 0.005 in the 1000 Genomes Project Database, the Exome Aggregation Consortium (ExAC) browser, and the Novogene database, or they would be removed as common ones. The pathogenic variants identified were verified by polymerase chain reaction. The sequencing results were analyzed by Chromas 2.1 software.

RESULTS

Two novel pathogenic variants (NM_000356.3: c.537del and NM_000356.3: c.1965_1966dupGG) and 2 known pathogenic variants (NM_000356.3: c.1535del, NM_000356.3: c.4131_4135del) were identified within TCOF1 which are predicted to lead to premature termination codons resulting in a truncated protein. There was a known missense SNP (NM_015972.3: c.139G>A) within POLR1D. No phenotype-genotype correlation was observed. Instead, these 8 patients demonstrated the high genotypic and phenotypic heterogeneity of TCS.

CONCLUSIONS

This study expands on the pathogenic gene pool of Chinese patients with TCS. Besides the great variation among patients which is similar to international reports, Chinese patients have their own characteristics in clinical phenotype and pathogenesis mutations.

De novo TCOF1 mutation in Treacher Collins syndrome

OBJECTIVE

To analyze the genetic cause of a hearing loss child with the Treacher Collins syndrome (TCS) phenotypes of malar hypoplasia, micrognathia, antimongoloid slanting palpebral fissures and cup ears.

METHODS

Clinical analysis, hearing tests, chromosomal microarray analysis (CMA) and whole exome sequencing (WES) were performed on the family members.

RESULTS

The 6 months old boy with a range of Treacher Collins syndrome phenotypes including malar hypoplasia, micrognathia, antimongoloid slanting palpebral fissures, cup ears, and hearing loss. While CMA analyses did not detect significant deletion or duplication, WES analysis identified a novel nonsense mutation c.163C > T (p.Q55X) in exon 2 of TCOF1 gene. Sanger sequencing analysis confirmed the mutation in the patient, but not in his parents.

CONCLUSION

This article reports a novel nonsense mutation located at exon 2 in TCOF1 gene, which predicts premature protein termination of treacle, indicating that haploinsufficiency of TCOF1 gene is responsible for Treacher Collins syndrome. Our study increases the cohort of Chinese TCS patients, and expands the TCS variation spectrum.

The Cardiac Neural Crest Cells in Heart Development and Congenital Heart Defects

The neural crest (NC) is a multipotent and temporarily migratory cell population stemming from the dorsal neural tube during vertebrate embryogenesis. Cardiac neural crest cells (NCCs), a specified subpopulation of the NC, are vital for normal cardiovascular development, as they significantly contribute to the pharyngeal arch arteries, the developing cardiac outflow tract (OFT), cardiac valves, and interventricular septum. Various signaling pathways are shown to orchestrate the proper migration, compaction, and differentiation of cardiac NCCs during cardiovascular development. Any loss or dysregulation of signaling pathways in cardiac NCCs can lead to abnormal cardiovascular development during embryogenesis, resulting in abnormalities categorized as congenital heart defects (CHDs). This review focuses on the contributions of cardiac NCCs to cardiovascular formation, discusses cardiac defects caused by a disruption of various regulatory factors, and summarizes the role of multiple signaling pathways during embryonic development. A better understanding of the cardiac NC and its vast regulatory network will provide a deeper insight into the mechanisms of the associated abnormalities, leading to potential therapeutic advancements.

Genetic Susceptibility Loci in Genomewide Association Study of Cluster Headache

Objective

Identifying common genetic variants that confer genetic risk for cluster headache.

Methods

We conducted a case–control study in the Dutch Leiden University Cluster headache neuro‐Analysis program (LUCA) study population (n = 840) and unselected controls from the Netherlands Epidemiology of Obesity Study (NEO; n = 1,457). Replication was performed in a Norwegian sample of 144 cases from the Trondheim Cluster headache sample and 1,800 controls from the Nord‐Trøndelag Health Survey (HUNT). Gene set and tissue enrichment analyses, blood cell‐derived RNA‐sequencing of genes around the risk loci and linkage disequilibrium score regression were part of the downstream analyses.

Results

An association was found with cluster headache for 4 independent loci (r² < 0.1) with genomewide significance (p < 5 × 10⁻⁸), rs11579212 (odds ratio [OR] = 1.51, 95% confidence interval [CI] = 1.33–1.72 near RP11‐815 M8.1), rs6541998 (OR = 1.53, 95% CI = 1.37–1.74 near MERTK), rs10184573 (OR = 1.43, 95% CI = 1.26–1.61 near AC093590.1), and rs2499799 (OR = 0.62, 95% CI = 0.54–0.73 near UFL1/FHL5), collectively explaining 7.2% of the variance of cluster headache. SNPs rs11579212, rs10184573, and rs976357, as proxy SNP for rs2499799 (r² = 1.0), replicated in the Norwegian sample (p < 0.05). Gene‐based mapping yielded ASZ1 as possible fifth locus. RNA‐sequencing indicated differential expression of POLR1B and TMEM87B in cluster headache patients.

Interpretation

This genomewide association study (GWAS) identified and replicated genetic risk loci for cluster headache with effect sizes larger than those typically seen in complex genetic disorders. ANN NEUROL 2021;90:203–216

Hippo-Yap Pathway Orchestrates Neural Crest Ontogenesis

Neural crest (NC) cells are a migratory stem cell population in vertebrate embryogenesis that can give rise to multiple cell types, including osteoblasts, chondrocytes, smooth muscle cells, neurons, glia, and melanocytes, greatly contributing to the development of different tissues and organs. Defects in NC development are implicated in many human diseases, such as numerous syndromes, craniofacial aberration and congenital heart defects. Research on NC development has gained intense interest and made significant progress. Recent studies showed that the Hippo-Yap pathway, a conserved fundamental pathway with key roles in regulation of cell proliferation, survival, and differentiation, is indispensable for normal NC development. However, the roles and mechanisms of the Hippo-Yap pathway in NC development remain largely unknown. In this review, we summarize the key functions of the Hippo-Yap pathway indicated in NC induction, migration, proliferation, survival, and differentiation, as well as the diseases caused by its dysfunction in NC cells. We also discuss emerging current and future studies in the investigation of the Hippo-Yap pathway in NC development.

Long-term treatment outcomes from a patient's perspective with Treacher Collins syndrome

The management of patients with Treacher Collins Syndrome (TCS) is complex and involves many different specialists within multidisciplinary teams (MDT). The treatment pathway extends from birth well into adulthood and is associated with a heavy burden of care. Due to the extensive nature of the interaction with these patients, MDT members have opportunities to provide enhanced patient-centred care and support.This case report provides an overview of the current knowledge of the aetiology of TCS, the management of these patients and provides a unique perspective from one of the coauthors who has TCS and reports on his treatment experiences and long-term treatment outcomes. By having a better understanding of the impact of TCS and treatment provided, MDT members can not only provide improved clinical treatment but also offer improved patient experiences for those with craniofacial anomalies in particular an increased awareness of the psychosocial challenges they endure.

Diabetes, Oxidative Stress, and DNA Damage Modulate Cranial Neural Crest Cell Development and the Phenotype Variability of Craniofacial Disorders

Craniofacial malformations are among the most common birth defects in humans and they often have significant detrimental functional, aesthetic, and social consequences. To date, more than 700 distinct craniofacial disorders have been described. However, the genetic, environmental, and developmental origins of most of these conditions remain to be determined. This gap in our knowledge is hampered in part by the tremendous phenotypic diversity evident in craniofacial syndromes but is also due to our limited understanding of the signals and mechanisms governing normal craniofacial development and variation. The principles of Mendelian inheritance have uncovered the etiology of relatively few complex craniofacial traits and consequently, the variability of craniofacial syndromes and phenotypes both within families and between families is often attributed to variable gene expression and incomplete penetrance. However, it is becoming increasingly apparent that phenotypic variation is often the result of combinatorial genetic and non-genetic factors. Major non-genetic factors include environmental effectors such as pregestational maternal diabetes, which is well-known to increase the risk of craniofacial birth defects. The hyperglycemia characteristic of diabetes causes oxidative stress which in turn can result in genotoxic stress, DNA damage, metabolic alterations, and subsequently perturbed embryogenesis. In this review we explore the importance of gene-environment associations involving diabetes, oxidative stress, and DNA damage during cranial neural crest cell development, which may underpin the phenotypic variability observed in specific craniofacial syndromes.

Multivariate Analysis Identifies Eight Novel Loci Associated with Meat Productivity Traits in Sheep

Despite their economic value, sheep remain relatively poorly studied animals in terms of the number of known loci and genes associated with commercially important traits. This gap in our knowledge can be filled in by performing new genome-wide association studies (GWAS) or by re-analyzing previously documented data using novel powerful statistical methods. This study is focused on the search for new loci associated with meat productivity and carcass traits in sheep. With a multivariate approach applied to publicly available GWAS results, we identified eight novel loci associated with the meat productivity and carcass traits in sheep. Using an in silico follow-up approach, we prioritized 13 genes in these loci. One of eight novel loci near the FAM3C and WNT16 genes has been replicated in an independent sample of Russian sheep populations (N = 108). The novel loci were added to our regularly updated database increasing the number of known loci to more than 140.

Identification of rare and common regulatory variants in pluripotent cells using population-scale transcriptomics

Induced pluripotent stem cells (iPSCs) are an established cellular system to study the impact of genetic variants in derived cell types and developmental contexts. However, in their pluripotent state, the disease impact of genetic variants is less known. Here, we integrate data from 1,367 human iPSC lines to comprehensively map common and rare regulatory variants in human pluripotent cells. Using this population-scale resource, we report hundreds of novel colocalization events for human traits specific to iPSCs, and find increased power to identify rare regulatory variants compared with somatic tissues. Finally, we demonstrate how iPSCs enable the identification of causal genes for rare diseases.

A Recurrent Variant in POLR1B, c.3007C>T; p.Arg1003Cys, Associated with Atresia of the External Canal and Microtia in Treacher Collins Syndrome Type 4

Treacher Collins syndrome (TCS) is a heterogenous malformation syndrome characterized by a distinct facial appearance including downslanting palpebral fissures, malar hypoplasia, conductive hearing loss, and mandibular hypoplasia. Recently, a new causative gene, POLR1B, encoding DNA-directed RNA polymerase I subunit RPA2, was identified as a fourth type of TCS (TCS4). We describe another patient with TCS4 caused by a recurrent POLR1B variant, c.3007C>T; p.Arg1003Cys. Including our patient, all 4 patients with p.(Arg1003Cys) had atresia of the external auditory canal and microtia. All of the reported pathogenic variants in POLR1B were clustered at only 2 residues. Our patient highlights the genotype-phenotype correlation in TCS4 associated with POLR1B.

Bioinformatics analysis of candidate genes involved in ethanol-induced microtia pathogenesis based on a human genome database: GeneCards

OBJECTIVE

Ethanol used by women during pregnancy increases the risk for microtia in the foetus. Traditionally, laboratory experiments and Mouse Genome Informatics (MGI) have been used to explore microtia pathogenesis. The aim of this study was to screen and verify hub genes involved in ethanol-induced microtia and to explore the potential molecular mechanisms.

METHODS

Overlapping genes related to ethanol and microtia were acquired from the GeneCards database and filtered by confidence score. These genes were further analysed via bioinformatics. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis results were visualized with the clusterProfiler R package. A protein-protein interaction (PPI) network was constructed based on data from the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database.

RESULTS

Overall, 41 genes related to both ethanol and microtia were identified. The genes most relevant to ethanol-induced microtia pathogenesis included FGFR-2, FGFR-3, FGF-8, TP53, IGF1, SHH, CTNNB1, and PAX6, among others. Most genes were strongly enriched for tissue and organ development in GO analysis. Additionally, many genes were enriched in the Ras, FoxO, MAPK, and PI3K-Akt signalling pathways in KEGG analysis.

CONCLUSIONS

Bioinformatics analysis was conducted on genes currently known to be related to ethanol-induced microtia pathogenesis. We propose that mechanisms involving FGF-family genes, TP53, IGF1 and SHH contribute significantly to ethanol-induced microtia and the accompanying malformation of other structures.

TRPV1 Activation Promotes β-arrestin2 Interaction with the Ribosomal Biogenesis Machinery in the Nucleolus:Implications for p53 Regulation and Neurite Outgrowth

Transient receptor potential vanilloids (TRPV1) are non-selective cation channels that sense and transduce inflammatory pain signals. We previously reported that activation of TRPV1 induced the translocation of β-arrestin2 (ARRB2) from the cytoplasm to the nucleus, raising questions about the functional role of ARRB2 in the nucleus. Here, we determined the ARRB2 nuclear signalosome by conducting a quantitative proteomic analysis of the nucleus-sequestered L395Q ARRB2 mutant, compared to the cytosolic wild-type ARRB2 (WT ARRB2), in a heterologous expression system. We identified clusters of proteins that localize to the nucleolus and are involved in ribosomal biogenesis. Accordingly, L395Q ARRB2 or WT ARRB2 after capsaicin treatment were found to co-localize and interact with the nucleolar marker nucleophosmin (NPM1), treacle protein (TCOF1) and RNA polymerase I (POL I). We further investigated the role of nuclear ARRB2 signaling in regulating neuroplasticity. Using neuroblastoma (neuro2a) cells and dorsal root ganglia (DRG) neurons, we found that L395Q ARRB2 mutant increased POL I activity, inhibited the tumor suppressorp53 (p53) level and caused a decrease in the outgrowth of neurites. Together, our results suggest that the activation of TRPV1 promotes the ARRB2-mediated regulation of ribosomal biogenesis in the nucleolus. The ARRB2-TCOF1-p53 checkpoint signaling pathway might be involved in regulating neurite outgrowth associated with pathological pain conditions.

[Three-dimensional measurement analysis of midface morphology in Treacher Collins syndromes]

Objective

To three-dimensionally calculate the craniofacial parameters of midface of patients with Treacher Collins syndrome (TCS) in China, in order to understand the changes in the spatial position relationship between the various anatomical structures of the midface.

Methods

CT imaging data of TCS patients and age- and gender-matched normal populations between January 2013 and July 2020 was retrospectively analyzed. A total of 33 cases met the selection criteria for inclusion in the study, including 14 cases in the TCS group and 19 cases in the control group. ProPlan CMF 3.0 software was used to perform three-dimensional digital reconstruction of the craniofacial bone, measure the anatomical parameters of the midface, and analyze its morphological structure; at the same time perform three-dimensional digital reconstruction of the upper airway for morphological analysis (measure upper airway volume).

Results

CT images analysis revealed that all 14 patients with TCS presented the typical features with downward slanting of the palpebral fissures and different degrees of zygomatico-orbital complex dysplasia. Cephalometric and morphological analysis of the midface revealed that, multiple transverse diameters of the midface of TCS patients were significantly decreased when compared with the control group ( P<0.05), such as the width of the maxillary base, the length of the maxillary complex, and some distances related to the nasal morphology; but the distance between bilateral orbitales increased in TCS group ( P<0.05). Several anteroposterior distances in TCS group were decreased significantly when compared to control group and the distance between the skull base point and the posterior nasal spine was the most shortened ( P<0.05). But there was no significant difference of the distance between nasion and anterior nasal spine, which represented anterior midface height, between groups ( P>0.05). The skull base angle and SNB angle (the angle between the sella point-nose root point-inferior alveolar seat point) of the TCS group both decreased when compared with the control group ( P<0.05), but there was no significant difference in SNA angle (the angle between the sella point-nose root point-upper alveolar seat point) between the two groups ( P>0.05). The total volume of the upper airway was (24 621.07±8 476.63) mm ³ in the TCS group, which was significantly lower than that of the control group [(32 864.21±13 148.74) mm ³] ( t=2.185, P=0.037).

Conclusion

The transverse distances, anteroposterior distances, and multiple craniofacial angles measurement of TCS patients were significantly decreased when compared to the control group, presented with different degrees of zygomatico-orbital complex dysplasia, nasal and maxillary dysplasia, but there was no obvious restriction in face height development. Reduced internal diameters of the upper airway maybe responsible for the decreased upper airway volume of patients with TCS.

Cryo-EM structures of human RNA polymerase I

RNA polymerase I (Pol I) specifically synthesizes ribosomal RNA. Pol I upregulation is linked to cancer, while mutations in the Pol I machinery lead to developmental disorders. Here we report the cryo-EM structure of elongating human Pol I at 2.7 Å resolution. In the exit tunnel, we observe a double-stranded RNA helix that may support Pol I processivity. Our structure confirms that human Pol I consists of 13 subunits with only one subunit forming the Pol I stalk. Additionally, the structure of human Pol I in complex with the initiation factor RRN3 at 3.1 Å resolution reveals stalk flipping upon RRN3 binding. We also observe an inactivated state of human Pol I bound to an open DNA scaffold at 3.3 Å resolution. Lastly, the high-resolution structure of human Pol I allows mapping of disease-related mutations that can aid understanding of disease etiology.

How Altered Ribosome Production Can Cause or Contribute to Human Disease: The Spectrum of Ribosomopathies

A number of different defects in the process of ribosome production can lead to a diversified spectrum of disorders that are collectively identified as ribosomopathies. The specific factors involved may either play a role only in ribosome biogenesis or have additional extra-ribosomal functions, making it difficult to ascribe the pathogenesis of the disease specifically to an altered ribosome biogenesis, even if the latter is clearly affected. We reviewed the available literature in the field from this point of view with the aim of distinguishing, among ribosomopathies, the ones due to specific alterations in the process of ribosome production from those characterized by a multifactorial pathogenesis.