Apical expansion of calvarial osteoblasts and suture patency is dependent on fibronectin cues.

The skull roof, or calvaria, is comprised of interlocking plates of bones that encase the brain. Separating these bones are fibrous sutures that permit growth. Currently, we do not understand the instructions for directional growth of the calvaria, a process which is error-prone and can lead to skeletal deficiencies or premature suture fusion (craniosynostosis, CS). Here, we identify graded expression of fibronectin (FN1) in the mouse embryonic cranial mesenchyme (CM) that precedes the apical expansion of calvaria. Conditional deletion of Fn1 or Wasl leads to diminished frontal bone expansion by altering cell shape and focal actin enrichment, respectively, suggesting defective migration of calvarial progenitors. Interestingly, Fn1 mutants have premature fusion of coronal sutures. Consistently, syndromic forms of CS in humans exhibit dysregulated FN1 expression, and we also find FN1 expression altered in a mouse CS model of Apert syndrome. These data support a model of FN1 as a directional substrate for calvarial osteoblast migration that may be a common mechanism underlying many cranial disorders of disparate genetic etiologies.

Mesenchymal Wnts are required for morphogenetic movements of calvarial osteoblasts during apical expansion.

Apical expansion of calvarial osteoblast progenitors from the cranial mesenchyme (CM) above the eye is integral to calvarial growth and enclosure of the brain. The cellular behaviors and signals underlying the morphogenetic process of calvarial expansion are unknown. Time-lapse light-sheet imaging of mouse embryos revealed calvarial progenitors intercalate in 3D in the CM above the eye, and exhibit protrusive and crawling activity more apically. CM cells express non-canonical Wnt/planar cell polarity (PCP) core components and calvarial osteoblasts are bidirectionally polarized. We found non-canonical ligand Wnt5a-/- mutants have less dynamic cell rearrangements and protrusive activity. Loss of CM-restricted Wntless (CM-Wls), a gene required for secretion of all Wnt ligands, led to diminished apical expansion of Osx+ calvarial osteoblasts in the frontal bone primordia in a non-cell autonomous manner without perturbing proliferation or survival. Calvarial osteoblast polarization, progressive cell elongation and enrichment for actin along the baso-apical axis were dependent on CM-Wnts. Thus, CM-Wnts regulate cellular behaviors during calvarial morphogenesis for efficient apical expansion of calvarial osteoblasts. These findings also offer potential insights into the etiologies of calvarial dysplasias.

Indentation induces instantaneous nuclear stiffening and unfolding of nuclear envelope wrinkles.

The nuclear envelope (NE) separates genomic DNA from the cytoplasm and regulates transport between the cytosol and the nucleus in eukaryotes. Nuclear stiffening enables the cell nucleus to protect itself from extensive deformation, loss of NE integrity, and genome instability. It is known that the reorganization of actin, lamin, and chromatin can contribute to nuclear stiffening. In this work, we show that structural alteration of NE also contributes to instantaneous nuclear stiffening under indentation. In situ mechanical characterization of cell nuclei in intact cells shows that nuclear stiffening and unfolding of NE wrinkles occur simultaneously at the indentation site. A positive correlation between the initial state of NE wrinkles, the unfolding of NE wrinkles, and the stiffening ratio (stiffness fold-change) is found. Additionally, NE wrinkles unfold throughout the nucleus outside the indentation site. Finite element simulation, which involves the purely passive process of structural unfolding, shows that unfolding of NE wrinkles alone can lead to an increase in nuclear stiffness and a reduction in stress and strain levels. Together, these results provide a perspective on how cell nucleus adapts to mechanical stimuli through structural alteration of the NE.

Surgery for internal rotation contracture in infancy may obviate the need for brachial plexus nerve reconstruction: early experience.

BACKGROUND: Shoulder internal rotation contracture and subluxation in the first year of life has long been recognized in some patients with brachial plexus birth injury (BPBI). Surgical management of shoulder pathology has traditionally been undertaken following nerve reconstruction as necessary. In some patients; however, shoulder pathology may impair or obscure functional neuromuscular recovery of the upper extremity. As a proof of concept, we report a highly selected subset of patients with BPBI in whom shoulder surgery undertaken before one year of age obviated the need for neuroma resection and nerve grafting. METHODS: A retrospective review was performed of all patients with upper trunk BPBI who underwent shoulder surgery before one year of age from 2015 to 2018. Upper extremity motor function was evaluated with preoperative and postoperative Active Movement Scale scores, Cookie tests, and the requirement for subsequent neuroma resection and nerve grafting. RESULTS: Fifteen patients with BPBI meeting the inclusion criteria underwent shoulder surgery (including a subscapularis slide and tendon transfers of the teres major and latissimus dorsi muscles) before 1 year of age. Preoperatively, no patients of the appropriate age passed the Cookie test for elbow flexion. Thirteen patients either passed the Cookie test or scored Active Movement Scale score 7 for elbow flexion at or before the last available follow-up undertaken at a median age of 3.4 [1.4, 5.2] years. One of those 13 patients underwent single fascicular distal nerve transfer to improve elbow flexion before subsequently passing the Cookie test. Two patients did not have sufficient follow-up to assess elbow flexion. CONCLUSION: Although the exact role of shoulder surgery in infancy for BPBI remains to be defined, the findings from this study provide proof of concept that early, targeted surgical treatment of the shoulder may obviate the need for brachial plexus nerve reconstruction in a highly selected group of infants with BPBI.

Shape-driven confluent rigidity transition in curved biological tissues.

Collective cell motions underlie structure formation during embryonic development. Tissues exhibit emergent multicellular characteristics such as jamming, rigidity transitions, and glassy dynamics, but there remain questions about how those tissue-scale dynamics derive from local cell-level properties. Specifically, there has been little consideration of the interplay between local tissue geometry and cellular properties influencing larger-scale tissue behaviors. Here, we consider a simple two-dimensional computational vertex model for confluent tissue monolayers, which exhibits a rigidity phase transition controlled by the shape index (ratio of perimeter to square root area) of cells, on surfaces of constant curvature. We show that the critical point for the rigidity transition is a function of curvature such that positively curved systems are likely to be in a less rigid, more fluid, phase. Likewise, negatively curved systems (saddles) are likely to be in a more rigid, less fluid, phase. A phase diagram we generate for the curvature and shape index constitutes a testable prediction from the model. The curvature dependence is interesting because it suggests a natural explanation for more dynamic tissue remodeling and facile growth in regions of higher surface curvature. Conversely, we would predict stability at the base of saddle-shaped budding structures without invoking the need for biochemical or other physical differences. This concept has potential ramifications for our understanding of morphogenesis of budding and branching structures.

IRX3/5 regulate mitotic chromatid segregation and limb bud shape.

Pattern formation is influenced by transcriptional regulation as well as by morphogenetic mechanisms that shape organ primordia, although factors that link these processes remain under-appreciated. Here we show that, apart from their established transcriptional roles in pattern formation, IRX3/5 help to shape the limb bud primordium by promoting the separation and intercalation of dividing mesodermal cells. Surprisingly, IRX3/5 are required for appropriate cell cycle progression and chromatid segregation during mitosis, possibly in a nontranscriptional manner. IRX3/5 associate with, promote the abundance of, and share overlapping functions with co-regulators of cell division such as the cohesin subunits SMC1, SMC3, NIPBL and CUX1. The findings imply that IRX3/5 coordinate early limb bud morphogenesis with skeletal pattern formation.

Primitive Myxoid Mesenchymal Tumor of Infancy With Brain Metastasis Case Report and Literature Review.

Primitive myxoid mesenchymal tumor of infancy (PMMTI), a rare soft tissue tumor with distinct characteristics. PMMTI tends to have an aggressive local course, with multiple relapses and poor response to treatment. Rare cases of distant metastases have been described before. We described the second case of PMMTI with brain metastasis.

Spatial mapping of tissue properties in vivo reveals a 3D stiffness gradient in the mouse limb bud.

Numerous hypotheses invoke tissue stiffness as a key parameter that regulates morphogenesis and disease progression. However, current methods are insufficient to test hypotheses that concern physical properties deep in living tissues. Here we introduce, validate, and apply a magnetic device that generates a uniform magnetic field gradient within a space that is sufficient to accommodate an organ-stage mouse embryo under live conditions. The method allows rapid, nontoxic measurement of the three-dimensional (3D) spatial distribution of viscoelastic properties within mesenchyme and epithelia. Using the device, we identify an anteriorly biased mesodermal stiffness gradient along which cells move to shape the early limb bud. The stiffness gradient corresponds to a Wnt5a-dependent domain of fibronectin expression, raising the possibility that durotaxis underlies cell movements. Three-dimensional stiffness mapping enables the generation of hypotheses and potentially the rigorous testing of mechanisms of development and disease.

Bone Health in Osteosarcoma at Presentation and Its Impact on Cancer Treatment: A Case Series of 3 Pediatric Patients.

Osteosarcoma is the most common pediatric malignant bone tumor. Concomitant osteoporosis has typically been attributed to oncologic therapy. The present case series is aimed to describe 3 patients who presented with osteoporosis or osteopenia before, or early in, their oncology treatment. In our patients, bone health and its complications had significant impacts including pain, reduced mobility, prolonged admission, and delays in recovery. Our patients experienced improvement with resection of their primary tumor and with bisphosphonate infusion. Future studies are required to determine the prevalence osteoporosis at presentation of osteosarcoma and the role of bisphosphonates.

Non-rhabdomyosarcoma soft tissue sarcomas diagnosed in patients at a young age. An overview of clinical, pathological, and molecular findings.

OBJECTIVE: Disease spectrum in pediatric sarcoma differs substantially from adults. We report a cohort of very young children with non-rhabdomyosarcoma soft tissue sarcoma (NRSTS) detailing their molecular features, treatment, and outcome. METHODS: We report features of consecutive children (age <2 years) with NRSTS (2000-2017). Archival pathological material was re-reviewed, with additional molecular techniques applied where indicated. RESULTS: Twenty-nine patients (16 females, 55%) were identified (median age 6 months; range 0-23). Most common diagnoses included infantile fibrosarcoma (IFS, n = 14, 48%), malignant rhabdoid tumor (MRT, n = 4, 14%), and undifferentiated sarcoma (n = 4, 14%). Twenty-seven of 29 (93%) had tumor molecular characterization to confirm diagnosis. Clinical presentation included a swelling/mass (n = 23, 79%). Disease extent was localized (n = 20, 69%), locoregional (n = 6, 21%), or metastatic (n = 3, 10%). Seventeen of 29 (59%) who underwent surgery achieved complete resection (R0). Other treatments included conventional chemotherapy (n = 26, 90%), molecularly targeted therapies (n = 3, 10%), and radiation (n = 5, 17%). At last follow-up (median 3 years; range 0.3-16.4), 23 (79%) were alive, disease-free and six (21%) had died of disease. All patients with IFS were alive and all those with MRT died. A cancer predisposition syndrome (CPS) was confirmed in three of 10 (30%) genetically tested patients. CONCLUSION: We recommend tumor molecular characterization in all young patients including evaluation for CPS to optimize treatment options and prognostication.

Mechanical stability of the cell nucleus - roles played by the cytoskeleton in nuclear deformation and strain recovery.

Extracellular forces transmitted through the cytoskeleton can deform the cell nucleus. Large nuclear deformations increase the risk of disrupting the integrity of the nuclear envelope and causing DNA damage. The mechanical stability of the nucleus defines its capability to maintain nuclear shape by minimizing nuclear deformation and allowing strain to be minimized when deformed. Understanding the deformation and recovery behavior of the nucleus requires characterization of nuclear viscoelastic properties. Here, we quantified the decoupled viscoelastic parameters of the cell membrane, cytoskeleton, and the nucleus. The results indicate that the cytoskeleton enhances nuclear mechanical stability by lowering the effective deformability of the nucleus while maintaining nuclear sensitivity to mechanical stimuli. Additionally, the cytoskeleton decreases the strain energy release rate of the nucleus and might thus prevent shape change-induced structural damage to chromatin.

The Iroquois homeobox proteins IRX3 and IRX5 have distinct roles in Wilms tumour development and human nephrogenesis.

Wilms tumour is a paediatric malignancy with features of halted kidney development. Here, we demonstrate that the Iroquois homeobox genes IRX3 and IRX5 are essential for mammalian nephrogenesis and govern the differentiation of Wilms tumour. Knock-out Irx3- /Irx5- mice showed a strongly reduced embryonic nephron formation. In human foetal kidney and Wilms tumour, IRX5 expression was already activated in early proliferative blastema, whereas IRX3 protein levels peaked at tubular differentiation. Accordingly, an orthotopic xenograft mouse model of Wilms tumour showed that IRX3-/- cells formed bulky renal tumours dominated by immature mesenchyme and active canonical WNT/ß-catenin-signalling. In contrast, IRX5-/- cells displayed activation of Hippo and non-canonical WNT-signalling and generated small tumours with abundant tubulogenesis. Our findings suggest that promotion of IRX3 signalling or inhibition of IRX5 signalling could be a route towards differentiation therapy for Wilms tumour, in which WNT5A is a candidate molecule for enforced tubular maturation. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

The Pediatric Toronto Extremity Salvage Score (pTESS): Validation of a Self-reported Functional Outcomes Tool for Children with Extremity Tumors.

BACKGROUND: The physical function of children with sarcoma after surgery has not been studied explicitly. This paucity of research is partly because of the lack of a sufficiently sensitive pediatric functional measure. The goal of this study was to establish and validate a standardized measure of physical function in pediatric patients with extremity tumors. QUESTIONS/PURPOSES: (1) What is the best format and content for new upper- and lower-extremity measures of physical function in the pediatric population? (2) Do the new measures exhibit floor and/or ceiling effects, internal consistency, and test-retest reliability? (3) Are the new measures valid? METHODS: In Phase 1, interviews with 17 consecutive children and adolescents with bone tumors were conducted to modify the format and content of draft versions of the pediatric Toronto Extremity Salvage Score (pTESS). In Phase 2, the pTESS was formally translated into French. In Phase 3, 122 participants between 7 and 17.9 years old with malignant or benign-aggressive bone tumors completed the limb-specific measure on two occasions. Older adolescents also completed the adult TESS. Floor and ceiling effects, internal consistency, test-retest reliability, and validity were evaluated. RESULTS: Feedback from interviews resulted in the removal, addition, and modification of draft items, and the pTESS-Leg and pTESS-Arm questionnaires were finalized. Both versions exhibited no floor or ceiling effects and high internal consistency (α > 0.92). The test-retest reliability was excellent for the pTESS-Leg (intraclass correlation coefficient [ICC] = 0.94; 95% CI, 0.90-0.97) and good for the pTESS-Arm (ICC = 0.86; 95% CI, 0.61-0.96). Known-group validity (ability to discriminate between groups) was demonstrated by lower mean pTESS-Leg scores for participants using gait aids or braces (mean = 68; SD = 21) than for those who did not (mean = 87; SD = 11; p < 0.001). There was no significant difference between pTESS arm scores among respondents using a brace (n = 5; mean = 73; SD = 11) and those without (n = 22; mean = 83; SD = 19; p = 0.13). To evaluate construct validity, we tested a priori hypotheses. The duration since chemotherapy correlated moderately with higher pTESS-Leg scores (r = 0.4; p < 0.001) but not with pTESS-Arm scores (r = 0.1; p = 0.80), and the duration since tumor resection correlated moderately with higher pTESS-Leg scores (r = 0.4; p < 0.001) but not pTESS-Arm scores (r = 0.2; p = 0.4). Higher VAS scores (that is, it was harder to do things) antecorrelated with both pTESS versions (pTESS-Leg: r = -0.7; p < 0.001; pTESS-Arm: r = -0.8; p < 0.001). To assess criterion validity, we compared the pTESS with the current "gold standard" (adult TESS). Among adolescents, strong correlations were observed between the TESS and pTESS-Leg (r = 0.97, p < 0.001) and pTESS-Arm (r = 0.9, p = 0.007). CONCLUSIONS: Both pTESS versions exhibited no floor or ceiling effects and had high internal consistency. The pTESS-Leg demonstrated excellent reliability and validity, and the pTESS-Arm demonstrated good reliability and reasonable validity. The pTESS is recommended for cross-sectional evaluation of self-reported physical function in pediatric patients with bone tumors. LEVEL OF EVIDENCE: Level II, outcome measurement development.

Usefulness of diffusion-weighted MRI in the initial assessment of osseous sarcomas in children and adolescents.

BACKGROUND: Concern regarding gadolinium deposition in the brain after repeated administration of intravenous gadolinium-based contrast agents has prompted evaluation of imaging alternatives. OBJECTIVE: The study purpose was to determine if magnetic resonance imaging (MRI) using conventional sequences with diffusion-weighted imaging (DWI) instead of gadolinium-based contrast-enhanced MRI is valid for local staging and guiding biopsies in osseous sarcomas. MATERIALS AND METHODS: Initial pretreatment MRI with DWI and gadolinium-based contrast-enhanced images in patients ≤ 18 years with histopathologically proven osseous sarcomas were included. Two radiologists blinded to collated demographic and clinical data, independently reviewed conventional/DWI and conventional/gadolinium-based contrast-enhanced MRI then conventional sequences alone, recording tumor size, skip lesions, necrosis, neurovascular invasion, enlarged lymph nodes and diffusion restriction. Discrepancies were resolved by a third reader. A single reader measured apparent diffusion coefficient (ADC) values in non-necrotic tumors, then correlated minimum ADC values -- with and without normalization to skeletal muscle -- with relative enhancement. RESULTS: Twenty-one patients (mean age: 11.3±4.2 years, 15 [71%] females) had 14 osteosarcomas and 7 Ewing sarcomas, 50% centered in the femur. Conventional/DWI versus conventional/gadolinium-based contrast-enhanced MRI showed agreement for tumor size estimation with significant associations for necrosis (P=0.021), neurovascular involvement (P<0.001) and enlarged lymph nodes (P=0.005). Diagnostic accuracy of conventional/DWI is comparable to conventional/gadolinium-based contrast-enhanced MRI and superior to conventional sequences alone. Comparison between minimum ADC values and relative enhancement showed no correlation (P>0.05). CONCLUSION: Significant associations of key imaging features in the initial assessment of osseous sarcomas support DWI as an alternative to gadolinium-based contrast-enhanced MRI. The lack of association between ADC values and relative enhancement suggests that they measure independent constructs, DWI dependent upon tumor cellularity and perfusion.

Osteofibrous Dysplasia of the Tibia in Children: Outcome Without Resection.

BACKGROUND: The proposed association between osteofibrous dysplasia and adamantinoma has led some to advocate resection of the entire lesion, which can require major subsequent reconstruction. However, this link remains unproven and there is some support in more recent literature for a less aggressive approach. This study aims to describe our experience managing pediatric tibial osteofibrous dysplasia with such an approach and to report functional outcomes in children treated thus. METHODS: A total of 28 cases of osteofibrous dysplasia in 25 patients were managed at a referral center for pediatric bone tumors with observation in the first instance, then limited surgical intervention if required to address pain and deformity. Surgery aimed to restore stability and alignment without excising the lesion. Clinical records provided basic clinical outcome measures involving walking, recreation, orthoses and school/work participation and patients provided a Musculoskeletal Tumour Society score (MSTS) where contactable. RESULTS: Mean age at presentation was 6.0 years and mean follow-up was 8.3 years. Only 8 patients required surgery. According to basic outcome measures, 13 patients were symptom-free. About 15 patients (17 cases) provided a MSTS and the mean score was 24 of 30. No transformation to adamantinoma was observed. Those who presented at a younger age and with bilateral disease more often required surgery and remained symptomatic. CONCLUSIONS: A less aggressive approach to pediatric tibial osteofibrous dysplasia achieves good functional outcomes and patient satisfaction in most cases. Surgery is required in the minority of cases. Transformation to adamantinoma was not observed in this series. We recommend patient education, clinical observation and reactive intervention if required, rather than proactive resection and reconstruction. LEVEL OF EVIDENCE: Level IV-case series.

Characterizing Inner Pressure and Stiffness of Trophoblast and Inner Cell Mass of Blastocysts.

It has long been recognized that mechanical forces underlie mammalian embryonic shape changes. Before gastrulation, the blastocyst embryo undergoes significant shape changes, namely, the blastocyst cavity emerges and expands, and the inner cell mass (ICM) forms and changes in shape. The embryo's inner pressure has been hypothesized to be the driving mechanical input that causes the expansion of the blastocyst cavity and the shape changes of the ICM. However, how the inner pressure and the mechanics of the trophoblast and the ICM change during development is unknown because of the lack of a suitable tool for quantitative characterization. This work presents a laser-assisted magnetic tweezer technique for measuring the inner pressure and Young's modulus of the trophoblast and ICM of the blastocyst-stage mouse embryo. The results quantitatively showed that the inner pressure and Young's modulus of the trophoblast and ICM all increase during progression of mouse blastocysts, providing useful data for understanding how mechanical factors are physiologically integrated with other cues to direct embryo development.

Cell ingression: Relevance to limb development and for adaptive evolution.

Cell ingression is an out-of-plane type of cell intercalation that is essential for the formation of multiple embryonic structures including the limbs. In particular, cell ingression underlies epithelial-to-mesenchymal transition of lateral plate cells to initiate limb bud growth, delamination of neural crest cells to generate peripheral nerve sheaths, and emigration of myoblasts from somites to assemble muscles. Individual cells that ingress undergo apical constriction to generate bottle shaped cells, diminish adhesion to their epithelial cell neighbors, and generate protrusive blebs that likely facilitate their ingression into a subepithelial tissue layer. How signaling pathways regulate the progression of delamination is important for understanding numerous developmental events. In this review, we focus on cellular and molecular mechanisms that drive cell ingression and draw comparisons between different morphogenetic contexts in various model organisms. We speculate that cell behaviors that facilitated tissue invagination among diploblasts subsequently drove individual cell ingression and epithelial-to-mesenchymal transition. Future insights that link signalling pathways to biophysical mechanisms will likely advance our comprehension of this phenomenon.

Biophysical regulation of early limb bud morphogenesis.

The physical basis of morphogenesis is a fascinating concern that has been a longstanding interest of developmental biologists. In this review, I attempt to incorporate earlier and recent biophysical concepts and data to explain basic features of early limb bud morphogenesis. In particular, I discuss the influence of mesenchymal cohesion and physical properties that might contribute to phase separation of the bud from the lateral plate, the possibility that the early dorsoventral limb bud axis is moulded by the surface ectoderm, and endogenous electric fields that might contribute to oriented cell movements which generate the early limb bud. A combination of quantitative biophysical experimentation and modelling will likely advance this field.

Concomitant Administration of High-dose Methotrexate and Low-dose Aspirin Without Any Delay in Methotrexate Clearance in a Patient With Osteosarcoma: A Case Report and Review of the Literature.

BACKGROUND: Methotrexate (MTX) is a commonly used agent in the treatment of oncology patients whose clearance depends on renal health maintaining glomerular filtration and tubular secretion. Thus concomitant use of other drugs that utilize the same mechanism of clearance are generally avoided as this may contribute to increased MTX-associated toxicity. OBSERVATION: Herein, we describe the use of low-dose aspirin with high-dose MTX in a patient with osteosarcoma. CONCLUSION: Concomitant aspirin use did not affect the clearance of high-dose MTX and the patient did not experience any MTX-related toxicity including mucositis or renal impairment.

Aggressive embryonal rhabdomyosarcoma in a 3-month-old boy: A clinical and molecular analysis.

Rhabdomyosarcoma (RMS) represents the most common soft tissue sarcoma in the pediatric age group. While RMS has been traditionally classified on the basis of its histological appearance (with embryonal and alveolar being most common), it is now clear that the PAX-FOXO1 fusion product drives prognosis. We report here a case of pelvic embryonal RMS in a 3-month-old male who was subsequently found to have developed brain metastases during the course of chemotherapy. Cytogenetic analysis of the brain metastases at the time of autopsy as well as next-generation sequencing analysis revealed a reciprocal translocation involving the SH3 domain containing ring finger 3 gene (SH3RF3, on chromosome 2q13) and the Lipase C gene (LIPC, on chromosome 15q21.3). Due to the poor quality of the pretreatment and postresection samples, cytogenetics and NGS analysis looking for the presence of this balanced translocation in these specimens could not be performed. To the authors' knowledge, this translocation has never been described in RMS. Further studies are needed to determine the biological and clinical implications of this novel translocation.