Recurrent agnathia-otocephaly caused by DNA replication slippage in PRRX1

PRRX1-TOP2A interaction is a malignancy-promoting factor in human malignant peripheral nerve sheath tumours

BACKGROUND

Paired related-homeobox 1 (PRRX1) is a transcription factor in the regulation of developmental morphogenetic processes. There is growing evidence that PRRX1 is highly expressed in certain cancers and is critically involved in human survival prognosis. However, the molecular mechanism of PRRX1 in cancer malignancy remains to be elucidated.

METHODS

PRRX1 expression in human Malignant peripheral nerve sheath tumours (MPNSTs) samples was detected immunohistochemically to evaluate survival prognosis. MPNST models with PRRX1 gene knockdown or overexpression were constructed in vitro and the phenotype of MPNST cells was evaluated. Bioinformatics analysis combined with co-immunoprecipitation, mass spectrometry, RNA-seq and structural prediction were used to identify proteins interacting with PRRX1.

RESULTS

High expression of PRRX1 was associated with a poor prognosis for MPNST. PRRX1 knockdown suppressed the tumorigenic potential. PRRX1 overexpressed in MPNSTs directly interacts with topoisomerase 2 A (TOP2A) to cooperatively promote epithelial-mesenchymal transition and increase expression of tumour malignancy-related gene sets including mTORC1, KRAS and SRC signalling pathways. Etoposide, a TOP2A inhibitor used in the treatment of MPNST, may exhibit one of its anticancer effects by inhibiting the PRRX1-TOP2A interaction.

CONCLUSION

Targeting the PRRX1-TOP2A interaction in malignant tumours with high PRRX1 expression might provide a novel tumour-selective therapeutic strategy.

Pathogenic variants in the paired-related homeobox 1 gene (PRRX1) cause craniosynostosis with incomplete penetrance

PURPOSE

Studies have previously implicated PRRX1 in craniofacial development, including demonstration of murine Prrx1 expression in the preosteogenic cells of the cranial sutures. We investigated the role of heterozygous missense and loss-of-function (LoF) variants in PRRX1 associated with craniosynostosis.

METHODS

Trio-based genome, exome, or targeted sequencing were used to screen PRRX1 in patients with craniosynostosis; immunofluorescence analyses were used to assess nuclear localization of wild-type and mutant proteins.

RESULTS

Genome sequencing identified 2 of 9 sporadically affected individuals with syndromic/multisuture craniosynostosis, who were heterozygous for rare/undescribed variants in PRRX1. Exome or targeted sequencing of PRRX1 revealed a further 9 of 1449 patients with craniosynostosis harboring deletions or rare heterozygous variants within the homeodomain. By collaboration, 7 additional individuals (4 families) were identified with putatively pathogenic PRRX1 variants. Immunofluorescence analyses showed that missense variants within the PRRX1 homeodomain cause abnormal nuclear localization. Of patients with variants considered likely pathogenic, bicoronal or other multisuture synostosis was present in 11 of 17 cases (65%). Pathogenic variants were inherited from unaffected relatives in many instances, yielding a 12.5% penetrance estimate for craniosynostosis.

CONCLUSION

This work supports a key role for PRRX1 in cranial suture development and shows that haploinsufficiency of PRRX1 is a relatively frequent cause of craniosynostosis.

Induction and expansion of human PRRX1+ limb-bud-like mesenchymal cells from pluripotent stem cells

Current protocols for the differentiation of human pluripotent stem cells (hPSCs) into chondrocytes do not allow for the expansion of intermediate progenitors so as to prospectively assess their chondrogenic potential. Here we report a protocol that leverages PRRX1-tdTomato reporter hPSCs for the selective induction of expandable and ontogenetically defined PRRX1⁺ limb-bud-like mesenchymal cells under defined xeno-free conditions, and the prospective assessment of the cells' chondrogenic potential via the cell-surface markers CD90, CD140B and CD82. The cells, which proliferated stably and exhibited the potential to undergo chondrogenic differentiation, formed hyaline cartilaginous-like tissue commensurate to their PRRX1-expression levels. Moreover, we show that limb-bud-like mesenchymal cells derived from patient-derived induced hPSCs can be used to identify therapeutic candidates for type II collagenopathy and we developed a method to generate uniformly sized hyaline cartilaginous-like particles by plating the cells on culture dishes coated with spots of a zwitterionic polymer. PRRX1⁺ limb-bud-like mesenchymal cells could facilitate the mass production of chondrocytes and cartilaginous tissues for applications in drug screening and tissue engineering.

The Mandibular and Hyoid Arches-From Molecular Patterning to Shaping Bone and Cartilage

The mandibular and hyoid arches collectively make up the facial skeleton, also known as the viscerocranium. Although all three germ layers come together to assemble the pharyngeal arches, the majority of tissue within viscerocranial skeletal components differentiates from the neural crest. Since nearly one third of all birth defects in humans affect the craniofacial region, it is important to understand how signalling pathways and transcription factors govern the embryogenesis and skeletogenesis of the viscerocranium. This review focuses on mouse and zebrafish models of craniofacial development. We highlight gene regulatory networks directing the patterning and osteochondrogenesis of the mandibular and hyoid arches that are actually conserved among all gnathostomes. The first part of this review describes the anatomy and development of mandibular and hyoid arches in both species. The second part analyses cell signalling and transcription factors that ensure the specificity of individual structures along the anatomical axes. The third part discusses the genes and molecules that control the formation of bone and cartilage within mandibular and hyoid arches and how dysregulation of molecular signalling influences the development of skeletal components of the viscerocranium. In conclusion, we notice that mandibular malformations in humans and mice often co-occur with hyoid malformations and pinpoint the similar molecular machinery controlling the development of mandibular and hyoid arches.

PRRX1 promotes malignant properties in human osteosarcoma

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PRRX1 is a poor-prognosis marker of human osteosarcoma.

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PRRX1 promotes proliferation, invasion, and drug resistance in human osteosarcoma.

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Forskolin was identified using RNA expression signatures of PRRX1 knockdown.

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Forskolin decreased proliferation and migration in human osteosarcoma.

Paired related homeobox 1 (PRRX1) is a marker of limb bud mesenchymal cells, and deficiency of p53 or Rb in Prrx1-positive cells induces osteosarcoma in several mouse models. However, the regulatory roles of PRRX1 in human osteosarcoma have not been defined. In this study, we performed PRRX1 immunostaining on 35 human osteosarcoma specimens to assess the correlation between PRRX1 level and overall survival. In patients with osteosarcoma, the expression level of PRRX1 positively correlated with poor prognosis or the ratio of lung metastasis. Additionally, we found PRRX1 expression on in 143B cells, a human osteosarcoma line with a high metastatic capacity. Downregulation of PRRX1 not only suppressed proliferation and invasion but also increased the sensitivity to cisplatin and doxorubicin. When 143B cells were subcutaneously transplanted into nude mice, PRRX1 knockdown decreased tumor sizes and rates of lung metastasis. Interestingly, forskolin, a chemical compound identified by Connectivity Map analysis using RNA expression signatures during PRRX1 knockdown, decreased tumor proliferation and cell migration to the same degree as PRRX1 knockdown. These results demonstrate that PRRX1 promotes tumor malignancy in human osteosarcoma.

Agnathia-otocephaly complex: a case report and a literature review on recurrence risk

Objectives

Agnathia-otocephaly complex (AOC) is an extremely rare, lethal disorder causing obstruction of the upper airway at birth due to absence of the mandible and hypoplasia of the oral cavity. Implications for future pregnancies need to be elucidated by parental counselling, as recurrence of AOC or associated comorbidities are possible. Very little is known on this subject, because of the rarity of the disorder and scarce data on genetic causes of this complex. The objectives of this study were to determine the recurrence risk and mode of inheritance for AOC based on current literature.

Contents

Recurrence of AOC or associated comorbidities within the family of an index case was reported in eight articles, describing 7 and 27 relatives, respectively. There were eight AOC cases in which the genetic cause was known. Mutations in 2 genes, orthodenticle homeobox 2 (OTX2) and paired related homeobox 1 (PRRX1), have been described. Due to its mainly sporadic appearance, recurrence risk is low. Counselling on recurrence risk is difficult, because of a broad heterogeneity with complex inheritance patterns and variability in phenotypic expression.

Outlook

Chromosomal analysis and exome sequencing in children with AOC will help unravel current aetiological uncertainties and could help in further reproductive decisions. We emphasize the need for timely diagnosis through ultrasound, providing parents with the opportunity to receive multidisciplinary counselling, giving them the chance to contemplate their management decisions.

A case of rare isolated agnathia and literature review

Agnathia is a rare congenital malformation with unknown etiology characterized by absence of the mandible, microstomia, and tongue aplasia, often found to have other anomalies including holoprosencephaly. The purpose of this paper was to describe the symptoms and imaging of a case of isolated agnathia and to conduct a comprehensive literature review of reported patients with isolated agnathia. Case reports of isolated agnathia are very rare, with most infants as stillborn. We report a child's management of isolated agnathia with microstomia and tongue aplasia. A literature review was performed with focus on diagnosis, airway, and feeding management of isolated agnathia. Polyhydramnios was a common pregnancy complication reported in 25 out of the 39 patients in the case study. Five infants were stillborn, while 23 died within the neonatal period. Of the deceased infants within the neonatal period, 19 died within minutes to hours while four died within days to weeks. There are nine patients with agnathia that survived past infancy. The results of this study suggest that isolated agnathia is a rare malformation which requires a multi-disciplinary approach for airway and feeding management.

Recurrent Fusions Between YAP1 and KMT2A in Morphologically Distinct Neoplasms Within the Spectrum of Low-grade Fibromyxoid Sarcoma and Sclerosing Epithelioid Fibrosarcoma

Sclerosing epithelioid fibrosarcoma (SEF) is an aggressive soft tissue sarcoma. In the majority of cases, there is overexpression of MUC4, and most cases show EWSR1-CREB3L1 gene fusions. A subset of SEF displays composite histologic features of SEF and low-grade fibromyxoid sarcoma (LGFMS). These "hybrid" tumors are more likely to harbor the FUS-CREB3L2 fusion, which is also seen in most LGFMS. We, here, characterize a series of 8 soft tissue neoplasms with morphologic features highly overlapping with LGFMS and SEF but lacking MUC4 expression and EWSR1/FUS-CREB3L gene fusions. Seven tumors showed fusions of the YAP1 and KMT2A genes, and 1 had a fusion of PRRX1 and KMT2D; all but 1 case displayed reciprocal gene fusions. At gene expression profiling, YAP1 and KMT2A/PRRX1 and KMT2D tumors were distinct from LGFMS/SEF. The patients were 4 female individuals and 4 male individuals aged 11 to 91 years. Tumors with known locations were in the lower extremity (5), trunk (2), and upper extremity (1); 3 originated in acral locations. Tumor size ranged from 2.5 to 13 cm. Proportions of SEF-like and LGFMS-like areas varied considerably among tumors. All tumors that showed infiltrative growth and mitotic figures per 10 HPFs ranged from 0 to 18. Tumor necrosis was present in 1 case. Follow-up was available for 5 patients (11 to 321 mo), 2 of whom developed local recurrences, and 1 died of metastatic disease. The clinical behavior of these soft tissue sarcomas remains to be further delineated in larger series with extended follow-up; however, our limited clinical data indicate that they are potentially aggressive.

Re-focusing on Agnathia-Otocephaly complex

OBJECTIVES

Agnathia-otocephaly complex is a rare condition characterized by mandibular hypoplasia or agnathia, ear anomalies (melotia/synotia) and microstomia with aglossia. This severe anomaly of the first branchial arch is most often lethal. The estimated incidence is less than 1 in 70.000 births, with etiologies linked to both genetic and teratogenic factors. Most of the cases are sporadic. To date, two genes have been described in humans to be involved in this condition: OTX2 and PRRX1. Nevertheless, the overall proportion of mutated cases is unknown and a significant number of patients remain without molecular diagnosis. Thus, the involvement of other genes than OTX2 and PRRX1 in the agnathia-otocephaly complex is not unlikely. Heterozygous mutations in Cnbp in mice are responsible for mandibular and eye defects mimicking the agnathia-otocephaly complex in humans and appear as a good candidate. Therefore, in this study, we aimed (i) to collect patients presenting with agnathia-otocephaly complex for screening CNBP, in parallel with OTX2 and PRRX1, to check its possible implication in the human phenotype and (ii) to compare our results with the literature data to estimate the proportion of mutated cases after genetic testing.

MATERIALS AND METHODS

In this work, we describe 10 patients suffering from the agnathia-otocephaly complex. All of them benefited from array-CGH and Sanger sequencing of OTX2, PRRX1 and CNBP. A complete review of the literature was made using the Pubmed database to collect all the patients described with a phenotype of agnathia-otocephaly complex during the 20 last years (1998-2019) in order (i) to study etiology (genetic causes, iatrogenic causes…) and (ii), when genetic testing was performed, to study which genes were tested and by which type of technologies.

RESULTS

In our 10 patients' cohort, no point mutation in the three tested genes was detected by Sanger sequencing, while array-CGH has allowed identifying a 107-kb deletion encompassing OTX2 responsible for the agnathia-otocephaly complex phenotype in 1 of them. In 4 of the 70 cases described in the literature, a toxic cause was identified and 22 out the 66 remaining cases benefited from genetic testing. Among those 22 patients, 6 were carrying mutation or deletion in the OTX2 gene and 4 in the PRRX1 gene. Thus, when compiling results from our cohort and the literature, a total of 32 patients benefited from genetic testing, with only 34% (11/32) of patients having a mutation in one of the two known genes, OTX2 or PRRX1.

CONCLUSIONS

From our work and the literature review, only mutations in OTX2 and PRRX1 have been found to date in patients, explaining around one third of the etiologies after genetic testing. Thus, agnathia-otocephaly complex remains unexplained in the majority of the patients, which indicates that other factors might be involved. Although involved in first branchial arch defects, no mutation in the CNBP gene was found in this study. This suggests that mutations in CNBP might not be involved in such phenotype in humans or that, unlike in mice, a compensatory effect might exist in humans. Nevertheless, given that agnathia-otocephaly complex is a rare phenotype, more patients have to be screened for CNBP mutations before we definitively conclude about its potential implication. Therefore, this work presents the current state of knowledge on agnathia-otocephaly complex and underlines the need to expand further the understanding of the genetic bases of this disorder, which remains largely unknown.

CLINICAL RELEVANCE

We made here an update and focus on the clinical and genetic aspects of agnathia-otocephaly complex as well as a more general review of craniofacial development.

Agnathia otocephaly: A case from the Katanga Copperbelt

BACKGROUND

Agnathia otocephaly is a rare craniofacial malformation complex characterised by absent/hypoplastic mandible, abnormally positioned ears meeting at level of neck. Besides mutations in two genes, PRRX1 and OTX2, a teratogenic cause has been suggested. A higher risk of congenital malformations has been associated with paternal work in mining in the Democratic Republic of the Congo's part of the Copperbelt.

CASE

We studied a female neonate with a clinical diagnosis of agnathia otocephaly, stillborn in Lubumbashi in 2019. The child's father had been working as an artisanal mineworker at the time of conception.

RESULTS

Genetic analysis did not reveal a causal mutation. The concentrations of cobalt, arsenic cadmium, and uranium in cord blood of the infant were much higher than those of normal neonates from a previous study.

CONCLUSION

In the absence of identified genetic causes, we hypothesize this case of agnathia otocephaly was related to an exogenous cause, possibly the father's mining-related job.

Epigenetic and Transcriptional Networks Underlying Atrial Fibrillation

Genome-wide association studies have uncovered over a 100 genetic loci associated with atrial fibrillation (AF), the most common arrhythmia. Many of the top AF-associated loci harbor key cardiac transcription factors, including PITX2, TBX5, PRRX1, and ZFHX3. Moreover, the vast majority of the AF-associated variants lie within noncoding regions of the genome where causal variants affect gene expression by altering the activity of transcription factors and the epigenetic state of chromatin. In this review, we discuss a transcriptional regulatory network model for AF defined by effector genes in Genome-wide association studies loci. We describe the current state of the field regarding the identification and function of AF-relevant gene regulatory networks, including variant regulatory elements, dose-sensitive transcription factor functionality, target genes, and epigenetic states. We illustrate how altered transcriptional networks may impact cardiomyocyte function and ionic currents that impact AF risk. Last, we identify the need for improved tools to identify and functionally test transcriptional components to define the links between genetic variation, epigenetic gene regulation, and atrial function.

[Molecular understanding of hierarchy and lineage of mesenchymal stem cells in vivo]

Mesenchymal stem cell (MSC) is a type of tissue stem cell. In clinical studies, cultured MSCs have shown important therapeutic effects on diseases via the reduction of neurological defects and regulation of immune responses. However, in vivo MSC localization, function, and properties are poorly understood; therefore, the molecular understanding of MSCs hierarchy is less advanced compared to hematopoietic stem cell hierarchy. To address these issues, we developed a method that enables us to visualize MSCs, manipulate their function, and analyze their molecular biology in vivo. Paired-related homeobox 1 (Prrx1)-positive cells are transiently observed during limb skeletal development in mice. Prrx1-positive cells form heterogeneous populations comprising multiple mesenchymal progenitors with different lineages that are developing into osteoblasts, chondrocytes, adipocytes, fibroblasts, and tendon and ligament cells. Our results suggest that osteoblast differentiation in the calvaria begins at the Prrx1⁺Sca1⁺ MSC stage with sequential progression to Prrx1⁺Sca1^- cells, then Osterix⁺Prrx1^-Sca1^- osteoblast precursors, which eventually form mature α1(I)-collagen⁺ osteoblasts. Using Runt-related transcription factor 2 (Runx2) conditional knockout mice, furthermore, we found that the essential period of Runx2 function in intramembranous ossification likely begins at the Prrx1⁺Sca1⁺ MSC stage and ends at the Osterix⁺Prrx1^-Sca1^- osteoblast precursor stage (before mature the α1(I)-collagen⁺ osteoblasts appear). This approach will enable us to understand the in vivo molecular biology features of MSCs, leading to their therapeutic applications for tissue repair and regeneration. This development can also contribute to the field of pluripotent stem cell by enabling the transplantation of lineage-restricted mesenchymal progenitors.

Exome sequencing of fetal anomaly syndromes: novel phenotype-genotype discoveries

The monogenic etiology of most severe fetal anomaly syndromes is poorly understood. Our objective was to use exome sequencing (ES) to increase our knowledge on causal variants and novel candidate genes associated with specific fetal phenotypes. We employed ES in a cohort of 19 families with one or more fetuses presenting with a distinctive anomaly pattern and/or phenotype recurrence at increased risk for lethal outcomes. Candidate variants were identified in 12 families (63%); in 6 of them a definite diagnosis was achieved including known or novel variants in recognized disease genes (MKS1, OTX2, FGFR2, and RYR1) and variants in novel disease genes describing new fetal phenotypes (CENPF, KIF14). We identified variants likely causal after clinical and functional review (SMAD3, KIF4A, and PIGW) and propose novel candidate genes (PTK7, DNHD1, and TTC28) for early human developmental disease supported by functional and cross-species phenotyping evidence. We describe rare and novel fetal anomaly syndromes and highlight the diagnostic utility of ES, but also its contribution to discovery. The diagnostic yield of the future application of prenatal ES will depend on our ability to increase our knowledge on the specific phenotype–genotype correlations during fetal development.

Syndromes associated with holoprosencephaly

Holoprosencephaly (HPE) is partial or complete failure of the forebrain to divide into hemispheres and can be an isolated finding or associated with a syndrome. Most cases of HPE are associated with a syndrome and roughly 40%-60% of fetuses with HPE have trisomy 13 which is the most common etiology of HPE. Other syndromes associated with HPE include additional aneuploidies like trisomy 18 and single gene disorders such as Smith-Lemli-Opitz syndrome. There are a number of syndromes such as pseudotrisomy 13 which do not have a known molecular etiology; therefore, this review has two parts: syndromes with a molecular diagnosis and syndromes where the etiology is yet to be found. As most HPE is syndromic, this review provides a comprehensive list and description of syndromes associated with HPE that may be used as a differential diagnosis and starting point for evaluating individuals with HPE.

Multiethnic GWAS Reveals Polygenic Architecture of Earlobe Attachment

The genetic basis of earlobe attachment has been a matter of debate since the early 20th century, such that geneticists argue both for and against polygenic inheritance. Recent genetic studies have identified a few loci associated with the trait, but large-scale analyses are still lacking. Here, we performed a genome-wide association study of lobe attachment in a multiethnic sample of 74,660 individuals from four cohorts (three with the trait scored by an expert rater and one with the trait self-reported). Meta-analysis of the three expert-rater-scored cohorts revealed six associated loci harboring numerous candidate genes, including EDAR, SP5, MRPS22, ADGRG6 (GPR126), KIAA1217, and PAX9. The large self-reported 23andMe cohort recapitulated each of these six loci. Moreover, meta-analysis across all four cohorts revealed a total of 49 significant (p < 5 × 10-8) loci. Annotation and enrichment analyses of these 49 loci showed strong evidence of genes involved in ear development and syndromes with auricular phenotypes. RNA sequencing data from both human fetal ear and mouse second branchial arch tissue confirmed that genes located among associated loci showed evidence of expression. These results provide strong evidence for the polygenic nature of earlobe attachment and offer insights into the biological basis of normal and abnormal ear development.

Paired related homeobox protein 1 regulates PDGF-induced chemotaxis of hepatic stellate cells in liver fibrosis

Activation of the platelet-derived growth factor (PDGF)/PDGF beta receptor (PDGFβR) axis has a critical role in liver fibrosis. However, the mechanisms that regulate the PDGF signaling are yet to be elucidated. The present study demonstrates that paired related homeobox protein 1 (Prrx1) is involved in PDGF-dependent hepatic stellate cell (HSCs) migration via modulation of the expression of metalloproteinases MMP2 and MMP9. PDGF elevated the level of Prrx1 through the activation of ERK/Sp1 and PI3K/Akt/Ets1 pathways. In vivo, an adenoviral-mediated Prrx1 shRNA administration attenuated liver fibrosis in thioacetamide-induced fibrotic models. These studies reveal a role of Prrx1 as a modulator of PDGF-dependent signaling in HSCs, and inhibiting its expression may offer a therapeutic approach for hepatic fibrosis.

Intercellular Genetic Interaction Between Irf6 and Twist1 during Craniofacial Development

Interferon Regulatory Factor 6 (IRF6) and TWIST1 are transcription factors necessary for craniofacial development. Human genetic studies showed that mutations in IRF6 lead to cleft lip and palate and mandibular abnormalities. In the mouse, we found that loss of Irf6 causes craniosynostosis and mandibular hypoplasia. Similarly, mutations in TWIST1 cause craniosynostosis, mandibular hypoplasia and cleft palate. Based on this phenotypic overlap, we asked if Irf6 and Twist1 interact genetically during craniofacial formation. While single heterozygous mice are normal, double heterozygous embryos (Irf6^+/−; Twist1^+/−) can have severe mandibular hypoplasia that leads to agnathia and cleft palate at birth. Analysis of spatiotemporal expression showed that Irf6 and Twist1 are found in different cell types. Consistent with the intercellular interaction, we found reduced expression of Endothelin1 (EDN1) in mandible and transcription factors that are critical for mandibular patterning including DLX5, DLX6 and HAND2, were also reduced in mesenchymal cells. Treatment of mandibular explants with exogenous EDN1 peptides partially rescued abnormalities in Meckel’s cartilage. In addition, partial rescue was observed when double heterozygous embryos also carried a null allele of p53. Considering that variants in IRF6 and TWIST1 contribute to human craniofacial defects, this gene-gene interaction may have implications on craniofacial disorders.

Prenatal Diagnosis of Isolated Agnathia-Otocephaly: A Case Report and Review of the Literature

Agnathia is a rare disease characterized by the absence of a mandible. Few cases of prenatally diagnosed isolated agnathia have been reported. We present a case report and review of the literature of prenatally diagnosed agnathia. A 38-year-old woman (gravida 0, para 0) was referred to our hospital at 28 weeks and 3 days of gestation for fetal evaluation because of polyhydramnios and suspected facial anomalies. Three-dimensional ultrasonography and MRI indicated agnathia. Premature rupture of the membranes occurred before the parents could reach a decision on the postnatal treatment. We performed emergency cesarean section on the second day of the 33rd week of gestation. The neonate was deemed nonresuscitable and he died of airway obstruction shortly after birth. Because agnathia is associated with very poor prognosis, accurate prenatal diagnosis and detailed counseling should be promptly provided before unexpected delivery to the parents for the determination of postnatal treatment.

Competition between Jagged-Notch and Endothelin1 Signaling Selectively Restricts Cartilage Formation in the Zebrafish Upper Face

The intricate shaping of the facial skeleton is essential for function of the vertebrate jaw and middle ear. While much has been learned about the signaling pathways and transcription factors that control facial patterning, the downstream cellular mechanisms dictating skeletal shapes have remained unclear. Here we present genetic evidence in zebrafish that three major signaling pathways − Jagged-Notch, Endothelin1 (Edn1), and Bmp − regulate the pattern of facial cartilage and bone formation by controlling the timing of cartilage differentiation along the dorsoventral axis of the pharyngeal arches. A genomic analysis of purified facial skeletal precursors in mutant and overexpression embryos revealed a core set of differentiation genes that were commonly repressed by Jagged-Notch and induced by Edn1. Further analysis of the pre-cartilage condensation gene barx1, as well as in vivo imaging of cartilage differentiation, revealed that cartilage forms first in regions of high Edn1 and low Jagged-Notch activity. Consistent with a role of Jagged-Notch signaling in restricting cartilage differentiation, loss of Notch pathway components resulted in expanded barx1 expression in the dorsal arches, with mutation of barx1 rescuing some aspects of dorsal skeletal patterning in jag1b mutants. We also identified prrx1a and prrx1b as negative Edn1 and positive Bmp targets that function in parallel to Jagged-Notch signaling to restrict the formation of dorsal barx1+ pre-cartilage condensations. Simultaneous loss of jag1b and prrx1a/b better rescued lower facial defects of edn1 mutants than loss of either pathway alone, showing that combined overactivation of Jagged-Notch and Bmp/Prrx1 pathways contribute to the absence of cartilage differentiation in the edn1 mutant lower face. These findings support a model in which Notch-mediated restriction of cartilage differentiation, particularly in the second pharyngeal arch, helps to establish a distinct skeletal pattern in the upper face.

The exquisite functions of the vertebrate face require the precise formation of its underlying bones. Remarkably, many of the genes required to shape the facial skeleton are the same from fish to man. In this study, we use the powerful zebrafish system to understand how the skeletal components of the face acquire different shapes during development. To do so, we analyze a series of mutants that disrupt patterning of the facial skeleton, and then assess how the genes affected in these mutants control cell fate in skeletal progenitor cells. From these genetic studies, we found that several pathways converge to control when and where progenitor cells commit to a cartilage fate, thus controlling the size and shape of cartilage templates for the later-arising bones. Our work thus reveals how regulating the timing of when progenitor cells make skeleton helps to shape the bones of the zebrafish face. As mutations in many of the genes studied are implicated in human craniofacial defects, differences in the timing of progenitor cell differentiation may also explain the wonderful diversity of human faces.

Role played by Prx1-dependent extracellular matrix properties in vascular smooth muscle development in embryonic lungs

Although there are many studies focusing on the molecular pathways underlying lung vascular morphogenesis, the extracellular matrix (ECM)-dependent regulation of mesenchymal cell differentiation in vascular smooth muscle development needs better understanding. In this study, we demonstrate that the paired related homeobox gene transcription factor Prx1 maintains the elastic ECM properties, which are essential for vascular smooth muscle precursor cell differentiation. We have found that Prx1(null) mouse lungs exhibit defective vascular smooth muscle development, downregulated elastic ECM expression, and compromised transforming growth factor (TGF)-β localization and signaling. Further characterization of ECM properties using decellularized lung ECM scaffolds derived from Prx1 mice demonstrated that Prx1 is required to maintain lung ECM stiffness. The results of cell culture using stiffness-controlled 2-D and 3-D synthetic substrates confirmed that Prx1-dependent ECM stiffness is essential for promotion of smooth muscle precursor differentiation for effective TGF-β stimulation. Supporting these results, both decellularized Prx1(null) lung ECM and Prx1(WT) (wild type) ECM scaffolds with blocked TGF-β failed to support mesenchymal cell to 3-D smooth muscle cell differentiation. These results suggest a novel ECM-dependent regulatory pathway of lung vascular development wherein Prx1 regulates lung vascular smooth muscle precursor development by coordinating the ECM biophysical and biochemical properties.

A mouse splice-site mutant and individuals with atypical chromosome 22q11.2 deletions demonstrate the crucial role for crkl in craniofacial and pharyngeal development

The 22q11.2 deletion syndrome (22q11DS) is thought to be a contiguous gene syndrome caused by haploinsufficiency for a variable number of genes with overlapping function during the development of the craniofacial, pharyngeal and cardiac structures. The complexity of genetic and developmental anomalies resulting in 22q11DS has made attributing causation to specific genes difficult. The CRKL gene resides within the common 3-Mb region, most frequently affected in 22q11DS, and has been shown to play an essential role in the development of tissues affected in 22q11DS. Here, we report the characterisation of a mouse strain we named 'snoopy', harbouring a novel Crkl splice-site mutation that results in a loss of Crkl expression. The snoopy strain exhibits a variable phenotype that includes micrognathia, pharyngeal occlusion, aglossia and holoprosencephaly, and altered retinoic acid and endothelin signalling. Together, these features are reminiscent of malformations occurring in auriculocondylar syndrome and agnathia-otocephaly complex, 2 conditions not previously associated with the CRKL function. Comparison of the features of a cohort of patients harbouring small 22q11.2 deletions centred over the CRKL gene, but sparing TBX1, highlights the role of CRKL in contributing to the craniofacial features of 22q11DS. These analyses demonstrate the central role of Crkl in regulating signalling events in the developing oropharyngeal complex and its potential to contribute to dysmorphology.

Emerging directions in the genetics of atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia and is associated with increased morbidity. As the population ages and the prevalence of AF continues to rise, the socioeconomic consequences of AF will become increasingly burdensome. Although there are well-defined clinical risk factors for AF, a significant heritable component is also recognized. To identify the molecular basis for the heritability of AF, investigators have used a combination of classical Mendelian genetics, candidate gene screening, and genome-wide association studies. However, these avenues have, as yet, failed to define the majority of the heritability of AF. The goal of this review is to describe the results from both candidate gene and genome-wide studies, as well as to outline potential future avenues for creating a more complete understanding of AF genetics. Ultimately, a more comprehensive view of the genetic underpinnings for AF will lead to the identification of novel molecular pathways and improved risk prediction of this complex arrhythmia.

Prenatal diagnosis of proximal partial trisomy 1q confirmed by comparative genomic hybridization array: molecular cytogenetic analysis, fetal pathology and review of the literature

BACKGROUND

Partial trisomy of the long arm of chromosome 1 (1q) is an exceptionally rare chromosomal abnormality and most of the prenatally diagnosed cases are associated with either complete (q11-qter) or large (q21-qter) duplications with pre- or perinatal demise of all reported cases. The most common sonographic findings associated with this karyotype abnormality include ventriculomegaly, increased nuchal translucency or nuchal fold, renal and cardiac abnormalities, craniofacial dysmorphism, and limb deformities. However, there is a wide spectrum of clinical manifestations due to the great variability in the extent of the duplication size and the possible contribution of additional genetic rearrangements in the final phenotype.

CASE REPORT

We report on a female fetus with sole partial trisomy 1q presenting with multiple structural malformations in the second trimester scan. Standard karyotyping demonstrated a large duplication on the proximal end of chromosome 1 [46,XX,dup(1)(pter→q31::q31→q12::q31→qter)] and further application of comparative genomic hybridization array confirmed the diagnosis and offered a precise characterization of the genetic defect.

CONCLUSION

A fetus with nonmosaic partial trisomy 1q that was prenatally diagnosed upon multiple abnormal ultrasound findings is presented. A detailed review of the currently available literature on the prenatal diagnostic approach of partial trisomy 1q in terms of fetal sonographic assessment and molecular cytogenetic investigation is also provided. The use of novel molecular techniques such comparative genomic hybridization array could shed further light on the correlation between the genes identified in the chromosomal region of interest and the resultant phenotype.

Otocephaly-Dysgnathia Complex: Description of Four Cases and Confirmation of the Role of OTX2

Otocephaly-dysgnathia complex is characterized by mandibular hypo- or aplasia, ear abnormalities, microstomia, and microglossia. Mutations in the orthodenticle homeobox 2 (OTX2) and paired related homeobox 1 (PRRX1) genes have recently been identified in some cases. We screened 4 otocephalic cases for these 2 genes and identified OTX2 mutations in 2 of them, thus confirming OTX2 is implicated in otocephaly. No PRRX1 mutation was identified. Interestingly, ocular involvement is not a constant feature in otocephalic cases with an OTX2 mutation. In one case, the mutation was inherited from a microphthalmic mother. The mechanism underlying this intrafamilial phenotypic variability remains unclear, but other genetic factors are likely to be necessary for the manifestation of the otocephalic phenotype.