Depletion of lamins B1 and B2 promotes chromatin mobility and induces differential gene expression by a mesoscale-motion-dependent mechanism

BACKGROUND

B-type lamins are critical nuclear envelope proteins that interact with the three-dimensional genomic architecture. However, identifying the direct roles of B-lamins on dynamic genome organization has been challenging as their joint depletion severely impacts cell viability. To overcome this, we engineered mammalian cells to rapidly and completely degrade endogenous B-type lamins using Auxin-inducible degron technology.

RESULTS

Using live-cell Dual Partial Wave Spectroscopic (Dual-PWS) microscopy, Stochastic Optical Reconstruction Microscopy (STORM), in situ Hi-C, CRISPR-Sirius, and fluorescence in situ hybridization (FISH), we demonstrate that lamin B1 and lamin B2 are critical structural components of the nuclear periphery that create a repressive compartment for peripheral-associated genes. Lamin B1 and lamin B2 depletion minimally alters higher-order chromatin folding but disrupts cell morphology, significantly increases chromatin mobility, redistributes both constitutive and facultative heterochromatin, and induces differential gene expression both within and near lamin-associated domain (LAD) boundaries. Critically, we demonstrate that chromatin territories expand as upregulated genes within LADs radially shift inwards. Our results indicate that the mechanism of action of B-type lamins comes from their role in constraining chromatin motion and spatial positioning of gene-specific loci, heterochromatin, and chromatin domains.

CONCLUSIONS

Our findings suggest that, while B-type lamin degradation does not significantly change genome topology, it has major implications for three-dimensional chromatin conformation at the single-cell level both at the lamina-associated periphery and the non-LAD-associated nuclear interior with concomitant genome-wide transcriptional changes. This raises intriguing questions about the individual and overlapping roles of lamin B1 and lamin B2 in cellular function and disease.

Influence of Body Posture on Internal Organ Dosimetry: Radiocesium Exposure Modeling Using Novel Posture-dependent Mesh Computational Phantoms

ABSTRACT

Current practice in reference internal dosimetry assumes a fixed upright standing posture is maintained throughout the dose-integration period. Recently, the mesh-type ICRP adult reference computational phantoms were transformed into different body postures (e.g., sitting, squatting) for use in occupational dose reconstruction applications. Here, for the first time, we apply this phantom series to the study of organ dose estimates following radionuclide intake. We consider the specific cases of 137 Cs and 134 Cs ingestion (accidental/occupational intake) with attention to variability in absorbed dose as a function of posture. The ICRP Publication 137 systemic biokinetic model for soluble cesium ingestion was used to compute organ-level time-integrated activity coefficients for reference adults, over a 50-y dose-integration period, for 134 Cs and 137 Cs (and its radioactive progeny 137m Ba). Mean posture time-allocations (h d -1 for standing, sitting, and lying) were taken from published survey data. In accord with modern dosimetry formalisms (e.g., MIRD, ICRP), a posture weighting factor was introduced that accounts for the fraction of time spent within each independent posture. Absorbed dose coefficients were computed using PHITS Monte Carlo simulations. ICRP 103 tissue weighting factors were applied along with the posture weighting factors to obtain committed effective dose per unit intake (Sv Bq -1 ). For 137 Cs ingestion, most organ absorbed dose coefficients were negligibly to marginally higher (< ~3%) for sitting or crouched (lying fetal/semi-fetal) postures maintained over the dose commitment period, relative to the upright standing posture. The committed effective dose coefficients were 1.3 × 10 -8 Sv Bq -1 137 Cs for standing, sitting, or crouched postures; thus, the posture-weighted committed effective dose was not significantly different than the committed effective dose for a maintained upright standing posture. For 134 Cs ingestion, most organ absorbed dose coefficients for the sitting and crouched postures were significantly larger than the standing posture, but the differences were still considered minor (< ~8% for most organs). The committed effective dose coefficients were 1.2 × 10 -8 Sv Bq -1 134 Cs for the standing posture and 1.3 × 10 -8 Sv Bq -1 134 Cs for the sitting or crouched posture. The posture-weighted committed effective dose was 1.3 × 10 -8 Sv Bq -1 134 Cs. Body posture has minor influence on organ-level absorbed dose coefficients and committed effective dose for ingestion of soluble 137 Cs or 134 Cs.

Personalized dosimetry of177Lu-DOTATATE: a comparison of organ- and voxel-level approaches using open-access images

¹⁷⁷Lu-DOTATATE (Lutathera^®) enables targeted radionuclide therapy of neuroendocrine tumors expressing somatostatin receptor type 2. Though patient-specific dosimetry estimates may be clinically important for predicting absorbed dose-effect relationships, there are multiple relevant dosimetry paradigms which are distinct in terms of clinical effort, numerical output and added-value. This work compares three different approaches for¹⁷⁷Lu-DOTATATE dosimetry, including 1) an organ-level approach based on reference phantom MIRD S-values scaled to patient-specific organ masses (MIRDcalc), 2) an organ-level approach based on Monte Carlo simulation in a patient-specific mesh phantoms (PARaDIM), and 3) a 3D approach based on Monte Carlo simulation in patient-specific voxel phantoms.Method. Serial quantitative SPECT/CT images for two patients receiving¹⁷⁷Lu-DOTATATE therapy were obtained from archive in theDeep Bluedatabase. For each patient, the serial CT images were co-registered to the first time point CT using a deformable registration technique aided by virtual landmarks placed in the kidney pelves and the lesion foci. The co-registered SPECT images were integrated voxel-wise to generate time-integrated activity maps. Lesions, kidneys, liver, spleen, lungs, compact bone, spongiosa, and rest of body were segmented at the first imaging time point and overlaid on co-registered integrated activity maps. The resultant segmentation was used for three purposes: 1) to generate patient-specific phantoms, 2) to determine organ-level time-integrated activities, and 3) to generate dose volume histograms from 3D voxel-based calculations.Results. Mean absorbed doses were computed for lesions and 48 tissues with MIRDcalc software. Mean organ absorbed doses and dose volume histograms were obtained for lesions and 6 tissues with the voxel Monte Carlo approach. Lesion- and organ-level absorbed dose estimates agreed within ±26% for the lesions and ±13% for the critical organs, among the different methods tested. Overall good agreement was observed with the dosimetry estimates from the NETTER-1 trial.Conclusions. For personalized¹⁷⁷Lu-DOTATATE dosimetry, a combined approach was determined to be valuable, which utilized two dose calculation methods supported by a single image processing workflow. In the absence of quantitative imaging limitations, the voxel Monte Carlo method likely provides valuable information to guide treatment by considering absorbed dose non-uniformity in lesions and organs at risk. The patient-scaled reference phantom method also provides valuable information, including absorbed dose estimates for non-segmented organs, and more accurate dose estimates for complex radiosensitive organs including the active marrow.

The Impact of Positron Range on PET Resolution, Evaluated with Phantoms and PHITS Monte Carlo Simulations for Conventional and Non-conventional Radionuclides

PURPOSE

The increasing interest and availability of non-standard positron-emitting radionuclides has heightened the relevance of radionuclide choice in the development and optimization of new positron emission tomography (PET) imaging procedures, both in preclinical research and clinical practice. Differences in achievable resolution arising from positron range can largely influence application suitability of each radionuclide, especially in small-ring preclinical PET where system blurring factors due to annihilation photon acollinearity and detector geometry are less significant. Some resolution degradation can be mitigated with appropriate range corrections implemented during image reconstruction, the quality of which is contingent on an accurate characterization of positron range.

PROCEDURES

To address this need, we have characterized the positron range of several standard and non-standard PET radionuclides (As-72, F-18, Ga-68, Mn-52, Y-86, and Zr-89) through imaging of small-animal quality control phantoms on a benchmark preclinical PET scanner. Further, the Particle and Heavy Ion Transport code System (PHITS v3.02) code was utilized for Monte Carlo modeling of positron range-dependent blurring effects.

RESULTS

Positron range kernels for each radionuclide were derived from simulation of point sources in ICRP reference tissues. PET resolution and quantitative accuracy afforded by various radionuclides in practicable imaging scenarios were characterized using a convolution-based method based on positron annihilation distributions obtained from PHITS. Our imaging and simulation results demonstrate the degradation of small animal PET resolution, and quantitative accuracy correlates with increasing positron energy; however, for a specific "benchmark" preclinical PET scanner and reconstruction workflow, these differences were observed to be minimal given radionuclides with average positron energies below ~ 400 keV.

CONCLUSION

Our measurements and simulations of the influence of positron range on PET resolution compare well with previous efforts documented in the literature and provide new data for several radionuclides in increasing clinical and preclinical use. The results will support current and future improvements in methods for positron range corrections in PET imaging.

N6-methyladenosine mRNA marking promotes selective translation of regulons required for human erythropoiesis

Many of the regulatory features governing erythrocyte specification, maturation, and associated disorders remain enigmatic. To identify new regulators of erythropoiesis, we utilize a functional genomic screen for genes affecting expression of the erythroid marker CD235a/GYPA. Among validating hits are genes coding for the N6-methyladenosine (m6A) mRNA methyltransferase (MTase) complex, including, METTL14, METTL3, and WTAP. We demonstrate that m6A MTase activity promotes erythroid gene expression programs through selective translation of ~300 m6A marked mRNAs, including those coding for SETD histone methyltransferases, ribosomal components, and polyA RNA binding proteins. Remarkably, loss of m6A marks results in dramatic loss of H3K4me3 marks across key erythroid-specific KLF1 transcriptional targets (e.g., Heme biosynthesis genes). Further, each m6A MTase subunit and a subset of their mRNAs targets are required for human erythroid specification in primary bone-marrow derived progenitors. Thus, m6A mRNA marks promote the translation of a network of genes required for human erythropoiesis.

Challenges to the student nurse on clinical placement in the rural setting: a review of the literature

CONTEXT

Positive learning experiences for students on clinical placement in rural settings have the potential for supporting the recruitment of qualified nurses to these areas. Recruitment of such nurses is a global concern because current shortages have resulted in decreased healthcare quality for rural residents. By understanding the challenges faced by nursing students unfamiliar with rural settings, educational and organizational strategies can be developed to promote positive learning experiences and so enhance recruitment.

ISSUE

A broad literature review was conducted to explore the question: 'What challenges do nursing students from urban communities experience while they are on clinical placements in rural areas, respecting that 'rural' is conceptualized differently by different stakeholders?' The review followed a 5 stage process: (1) identification of the problem and purpose of the review; (2) structured literature search; (3) data evaluation; (4) data analysis; and (5) presentation of findings. Thirteen studies were evaluated independently using tools from the Joanna Briggs Institute. The Ecological Model was the theoretical framework used for consideration of student challenges.

LESSONS LEARNED

This literature review revealed a paucity of studies that addressed the research question, with mostly Canadian and Australian studies meeting the inclusion criteria. Findings were organized according to Ecological Model levels and suggested that students face political, environmental, community-based, nursing-related, organizational, relational, and personal challenges on rural placement. Challenges vary according to the placement setting and available student supports. Policy, educational, and nursing practice recommendations include that students should be aware of the impact of limited resources in rural settings; that comprehensive orientation should be provided to clinical and community settings; and that an exploration of financial and distance education supports prior to the placement would be beneficial. Rural practice nurse educators also require support, and it is critical that they and those at the educational institution be receptive to student questions and learning needs.

Gingival liposarcoma: An unusual polyp

Liposarcomas account for up to 20% of all soft tissue tumours. They are uncommon in the head and neck. Sarcomas of the oral region (excluding lymphoma) account for 5% of all oral cancers, of which 10% are liposarcomas. Fewer than 80 cases have been reported in the world literature, most of which presented as expansile masses. The prognosis of liposarcoma is dependant on the histopathologic type, location, and adequacy of surgical treatment. Well-differentiated types have a good prognosis and minimal metastatic potential. We report a case of well-differentiated liposarcoma (lipoma-like subtype), that presented as a gingival polyp.

Oral cancer awareness of general medical and general dental practitioners

OBJECTIVE

To assess general medical practitioners' (GMPs') and general dental practitioners' (GDPs') awareness of prevention and early detection of oral cancer.

DESIGN

Cross-sectional questionnaire-based study.

SETTING

Primary care.

METHOD

Questionnaires were delivered to all GMPs and GDPs in Tayside, assessing oral examination habits, delivery of advice on oral cancer risk factors, knowledge of oral cancer risk factors and clinical appearance, preferred point of referral and requests for further information.

RESULTS

Response rates of 71% and 84% were obtained from GMPs and GDPs respectively. GMPs were less likely to examine patients' oral mucosa routinely, less likely to advise patients about risk factors for oral cancer, identified fewer risk factors for, and felt less confident about diagnosing oral cancer from clinical appearance than their dental counterparts. Seventy-one percent and 80% of GMPs and GDPs respectively requested further information about oral cancer.

CONCLUSION

Patients with oral lesions often present to their general medical practitioner. The incidence of oral cancer is rising in the United Kingdom, therefore the role of general medical practitioners in prevention and detection of oral cancer is becoming ever more important. This study highlights the need for improved education of general medical practitioners on oral cancer.

Prescribed medication taken by patients attending general dental practice: changes over 20 years

INTRODUCTION

Drug therapy can influence treatment planning and provision of dental care by general dental practitioners. There is little published information regarding the types of drug therapy taken by patients presenting for dental treatment in the United Kingdom.

OBJECTIVE

To record the drug therapy taken by patients presenting to general dental practice in 1995 and 2005 and compare to data reported in 1984.

SETTING

General dental practice.

STUDY DESIGN

Prospective cross-sectional study.

METHOD

Patients presenting to general dental practices in 1995 and 2005 were questioned regarding their current drug therapy. Patients' general medical practitioners were contacted if their drug history was unclear.

RESULTS

35%, 21.1% and 43.8% of patients were taking medications in 1984, 1995 and 2005 respectively. Statistically significant increases in the proportion taking three or more medications were evident in both 1995 and 2005.

DISCUSSION

In 2005 more patients presenting to dental practice were taking medications compared to 1984. There is an increasing trend toward polypharmacy. Therefore it is important to maintain a contemporaneous knowledge of pharmacology and drug interactions to ensure the provision of safe dental care.

Self-reported calcium intake and bone mineral content in children and adolescents

OBJECTIVE

We examined the relationship between self-reported calcium (Ca) intake and bone mineral content (BMC) in children and adolescents. We hypothesized that an expression of Ca adjusted for energy intake (EI), i.e., Ca density, would be a better predictor of BMC than unadjusted Ca because of underreporting of EI.

METHODS

Data were obtained on dietary intakes (repeated 24-hour recalls) and BMC (by DEXA) in a cross-section of 227 children aged 8 to 17 years. Bivariate and multivariate analyses were used to examine the relationship between Ca. Ca density, and the dependent variables total body BMC and lumbar spine BMC. Covariates included were height, weight, bone area. maturity age, activity score and EI.

RESULTS

Reported EI compared to estimated basal metabolic rate suggested underreporting of EI. Total body and lumbar spine BMC were significantly associated with EI, but not Ca or Ca density, in bivariate analyses. After controlling for size and maturity, multiple linear regression analysis revealed unadjusted Ca to be a predictor of BMC in males in the total body (p = 0.08) and lumbar spine (p = 0.01)). Unadjusted Ca was not a predictor of BMC at either site in females. Ca density was not a better predictor of BMC at either site in males or females.

CONCLUSIONS

The relationship observed in male adolescents in this study between Ca intake and BMC is similar to that seen in clinical trials. Ca density did not enable us to see a relationship between Ca intake and BMC in females, which may reflect systematic reporting errors or that diet is not a limiting factor in this group of healthy adolescents.

Highly active antiretroviral therapy normalizes the potential for MIP-1alpha production in HIV infection

DESIGN

The CC chemokines RANTES, MIP-1alpha and MIP-1beta are ligands for CCR5, which has been identified as the principal co-receptor for macrophage tropic strains of HIV-1. This study investigated whether the inducible levels of RANTES, MIP-1alpha and MIP-1beta produced by cultured whole blood samples related to different rates of progression of HIV infection and to the introduction of Nelfinavir-based highly active anti-retroviral therapy (HAART).

METHODS

Study subjects were HIV-positive and categorized as "slow progressors" (n= 8) or as "fast progressors" (n= 7); the latter group were treated with HAART. MIP-1alpha, MIP-1beta and RANTES production was determined using commercial ELISA kits.

RESULTS

The inducible production of MIP-1alpha by whole blood cells in culture was significantly depressed in patients starting therapy compared with "slow progressors" and "normal donors". The levels of MIP-1alpha significantly increased with therapy at 12 weeks compared with pre-HAART levels (P= O.05) and became comparable to that of "normals" and "slow progressors". Differences in the inducible levels of MIP-1beta and RANTES for the separate subject groups were not significant.

CONCLUSIONS

The increase in inducible MIP-1alpha production following HAART might suggest a role for the chemokines in HIV disease, either for monitoring the outcome of therapy of HIV disease, or as a direct therapeutic intervention.

Underreporting of energy intake, socioeconomic status, and expression of nutrient intake

The relationship between socioeconomic status and nutrient intake was examined in a recent study. The investigators used three different expressions of nutrient intake in an attempt to overcome the confounding effect of underreporting on interpretation of dietary intake data. Biologic validation attempts were inconclusive as to which expression yielded the most accurate results.

Effect of calcium supplementation is greater in prepubertal girls with low calcium intake

In a recent calcium supplementation trial, prepubertal girls with spontaneous calcium intake below 900 mg/day, when given additional calcium, had greater increases in bone mineral density than other girls. This lends support to the recently recommended Adequate Intake (AI) of 1300 mg/day calcium for American and Canadian children, although more studies on long-term effects of this intake level are still needed.

Helical (spiral) CT of the abdomen

Since its clinical introduction in the mid 1970s, techniques for CT have undergone many changes that have dramatically altered how CT scans are obtained. Helical (spiral) CT allows for faster acquisition of truly volumetric CT data than is possible with conventional scanners. Routine helical CT of the abdomen is now possible because of three major technical refinements: the development of the slip-ring gantry, improved detector efficiency, and greater tube cooling capability. This article reviews the technical principles that govern helical CT, the potential advantages and disadvantages of this technique, and initial clinical experience with helical CT of the abdomen.

Heterogeneity of fibroblast response in host-tumor cell-cell interactions in metastatic tumors

The spread and invasion of tumor cells into host tissues are associated with the release of elevated levels of collagenolytic activity of both host and tumor cell origins. However, the mechanisms of regulation of the enzyme activity is still unresolved. Histological examination of human and animal tumors revealed morphological changes in stromal fibroblasts and mast cells at the tumor periphery. Numerous mast cells appeared at microfoci along the tumor: host tissue junction and mast cell degranulation were associated with collagenolysis. In vitro studies, using rat mammary adenocarcinoma and human lung adenocarcinoma cells, showed that both tumor cells and host fibroblasts participate in matrix degradation. Tumor-associated stromal fibroblasts released higher levels of enzyme activity than normal fibroblasts and were more responsive to stimulation by tumor-conditioned media and soluble mast cell products. Host fibroblasts appear to be heterogeneous populations of responsive and nonresponsive subpopulations based on their response to tumor- or mast-cell-mediated stimulation of collagenase release. Fibroblast subpopulations were obtained by density fractionation of serum-deprived, synchronized confluent fibroblasts on discontinuous Percoll gradient. Density-fractionated fibroblast subpopulations differed in their response to stimulation by mast cell products and tumor-cell-conditioned media. The stimulatory activity of tumor-cell-conditioned media also varied as a function of the metastatic potential of the tumor cells. The data suggest that cellular interactions between tumor cells and select subpopulations of host fibroblasts at the tumor periphery play a key role in host tissue degradation. However, heterogeneity of stromal fibroblasts may determine the site and extent of the tissue damage at foci of tumor invasion.

Chemotactic response of rat mammary adenocarcinoma cell clones to tumor-derived cytokines

A cytokine with an apparent molecular weight of 53,000 daltons was isolated from serum-free medium conditioned by MTLn3 cells or from homogenates of MTLn3 cells, a highly metastatic variant of the rat 13762NF mammary adenocarcinoma. The chemotactic responses of MTLn3 and the low metastatic variant MTLn2 cells to this cytokine were tested in vitro using modified Boyden chambers. Both the chemotactic and chemokinetic movements of MTLn3 cells were stimulated by the MTLn3-derived cytokine. In addition, the MTLn3-derived cytokine stimulated a relatively small, but significant chemotactic migration of MTLn2 tumor cells, while these cells did not respond to medium conditioned by MTLn2 cells. MTLn3 cells themselves did not respond chemotactically to type I collagen or medium conditioned by MTLn2 cells. These results suggest that the chemotactic response may be a function of metastatic potential of the invading tumor cells. The production of tumor cytokines that enhance tumor cell motility may thus represent a phenotypic difference between 13762NF tumor cell subpopulations of high and low metastatic potential.

Mast cells and matrix degradation at sites of tumour invasion in rat mammary adenocarcinoma

Significant numbers of mast cells have been demonstrated histologically around the periphery of the invasive rat mammary adenocarcinoma 13672NF. The number of mast cells at microfoci along the tumour:host tissue junction was significantly greater than that found in normal mammary tissues, and few mast cells were detected within the tumour itself. Mast cell degranulation, often associated with disruption and lysis of the connective tissue matrix, was a common feature in later stages of tumour proliferation. When soluble products derived from purified rat peritoneal mast cells were added to monolayer cultures of rat stromal fibroblasts or tumour cells they stimulated a significant increase in total collagenase production, and the mast cell products were also capable of activating the latent collagenases thus produced. Histological examination indicated that degradation of local collagenous matrix was a common feature of mast cell degranulation, an observation possibly explained by the release of mast cell enzymes and/or the potential of this cell to modulate the expression of collagenolytic activity by surrounding cells. These observations suggest that, at least in some tumours, mast cells contribute to the connective tissue breakdown commonly associated with tumour invasiveness and metastatic spread.

Host-mediated effectors of tumor invasion: role of mast cells in matrix degradation

The role of collagenolytic enzymes in tumor invasion and metastasis has been emphasized, but the source of enzyme activity has remained unclear. Degradation of stromal connective tissue is a common feature of invasive neoplasia, and host-tumor cell interactions are probably important for localized collagenolysis. We have examined the role of mast cells in malignant cell invasion using cells derived from the rat mammary adenocarcinoma 13762NF. Histologic studies have shown increased numbers of mast cells at the zone of tumor invasion. Mast cell products and conditioned medium from such cells stimulated the production of collagenolytic enzymes by stromal fibroblasts as well as certain subpopulations of tumor cells in vitro. The tumor cell response to mast cell-mediated stimulation of collagenolysis appears to be related to the metastatic potential of the tumor cell. A subpopulation of host fibroblasts derived from the invading tumor zone was also found to be more responsive to mast cell factors than normal fibroblasts, as judged by collagenase production. Thus the mast cell has the potential to induce collagenolytic activity from both host fibroblasts and tumor cells.

Identifying scoliosis in the adolescent with thermography: a preliminary study

Early diagnosis of adolescent idiopathic scoliosis is essential to prevent severe deformity. The accuracy of thermographic examination of the spine in the detection of minor degrees of curvature has been assessed in 125 asymptomatic young persons mean age 13.4 +/- 0.8 years who were also examined clinically and by spinal X-ray. Assessment of thermograms selected at random from the group of 154 young subjects showed that thermography has a sensitivity of 98.2% and a specificity of 91.0% in the identification of scoliosis when compared with radiography. Thermographic examination of the spine is simple, noninvasive and provides a permanent recording which is easily interpreted. It may provide an ideal method for use in large-scale prospective surveys. The criteria used to detect the thermographic abnormality associated with idiopathic scoliosis was derived from the spinal thermograms of 29 patients, mean age 10.25 +/- 4.65 years with known scoliosis, mean angle of curve 27 degrees +/- 12 degrees. In contrast to the thermal symmetry of the normal spine, all the thermograms of these patients show asymmetry, characteristically an increase in thermal emission on the concave aspect of the curve. Eight of the 16 patients with scoliosis with minor curves and a characteristic thermogram were not detected clinically. There were 25 asymmetrical thermograms in the asymptomatic group. Three of these patients had a simple postural defect, 5 had dorsal kyphosis and 16 had idiopathic scoliosis. Postural defects and kyphosis were readily recognized on clinical examination and did not produce the characteristic scoliotic thermogram.