A Hazard-Based Framework for Identifying Safer Alternatives to Classes of Chemicals: A Case Study on Phthalates in Consumer Products

BACKGROUND

Humans are exposed to hazardous chemicals found in consumer products. In 2019, the Pollution Prevention for Healthy People and Puget Sound Act was passed in Washington State. This law is meant to reduce hazardous chemicals in consumer products and protect human health and the environment. The law directs the Washington State Department of Ecology to assess chemicals and chemical classes found in products, determine whether there are safer alternatives, and make regulatory determinations.

OBJECTIVES

To implement the law, the Department of Ecology developed a hazard-based framework for identifying safer alternatives to classes of chemicals.

METHODS

We developed a hazard-based framework, termed the "Criteria for Safer," to set a transparent bar for determining whether new chemical alternatives are safer than existing classes of chemicals. Our "Criteria for Safer" is a framework that builds on existing hazard assessment methodologies and published approaches for assessing chemicals and chemical classes.

DISCUSSION

We describe implementation of our criteria using a case study on the phthalates chemical class in two categories of consumer products: vinyl flooring and fragrances used in personal care and beauty products. Additional context and considerations that guided our decision-making process are also discussed, as well as benefits and limitations of our approach. This paper gives insight into our development and implementation of a hazard-based framework to address classes of chemicals in consumer products and will aid others working to build and employ similar approaches. https://doi.org/10.1289/EHP13549.

Early detection and intervention for young children with early developmental disabilities in Western Uganda: a mixed-methods evaluation

BACKGROUND

Early support for children with developmental disabilities is crucial but frequently unavailable in low-resource settings. We conducted a mixed-methods evaluation to assess the feasibility, acceptability, and impact of a programme of early detection and intervention for young children with developmental disabilities in Western Uganda.

METHODS

Early child development training for healthcare workers (HCWs) was implemented in three rural districts, and attendance was tracked. HCW knowledge and confidence were assessed pre-/post-intervention, and referral numbers tracked to evaluate impact. Facilitators were trained and mentored to deliver a participatory, group, early intervention programme (EIP) for young children with developmental disabilities and their families. Facilitators were tracked as they were identified, trained, and delivered the intervention, and attendance of families was tracked. Pre-/post-intervention assessments evaluated changes in family quality of life (PedsQL 2.0, Family Impact Module), and child nutritional outcomes. Focus group discussions with stakeholders also assessed feasibility, acceptability and impact.

RESULTS

Overall, 93 HCWs from 45 healthcare facilities received training. In the pre-/post-evaluation, median knowledge and confidence scores increased significantly (from 4.0 to 7.0 and from 2.7 to 4.7, respectively (p < 0.001)). HCWs reported feeling empowered to refer and offer care for families with a young child with disability. Referral rates increased significantly from 148 to 251 per annum (70%; p = 0.03). Eleven EIP facilitators were trained, and all delivered the intervention; 84 families were enrolled, of which 78% attended at least 6 out of 10 modules. Amongst those with paired pre-/post-intervention data (n = 48), total family quality of life scores increased significantly (21%, p < 0.001). Improvements were seen across all domains of quality of life, with the largest impacts on emotional functioning and social functioning (p < 0.001). The programme was acceptable to caregivers and facilitators. Caregivers reported improved knowledge, family relationships, hope, emotional wellbeing, and reduced self-stigma.

CONCLUSIONS

A programme of early detection and intervention for children with early developmental disabilities and their families was feasible and acceptable in a rural community-based Ugandan setting. HCW training positively impacted knowledge, confidence, attitudes, and referral rates. Families enrolled to the EIP reported significant improvements in quality of life. Important programmatic barriers identified included geographical spread, poverty, gender inequality, and stigma.

Trauma to the medial ray of the foot: A classification of patterns of injury and their management

AIMS

Fractures and dislocations of the midfoot are relatively uncommon but can be life changing injuries. Within the literature, there has been scant specific reference to the identification and management of medial ray injuries in midfoot trauma. Moreover, it is appreciated that these injuries are associated with poor outcomes. We aim to clearly define these injury characteristics and demonstrate fixation techniques.

PATIENTS AND METHODS

A retrospective review of the case notes and imaging was conducted for operatively treated midfoot injuries between January 2013 and January 2018.

RESULTS

161 patients were identified, 31 of these with imaging and operative diagnosis suggestive of medial ray injury. Studying these 31 injuries revealed five patterns of injury.

CONCLUSION

When treating midfoot trauma, it is important to fully understand the injury pattern as this dictates the principles and techniques of fixation. Identification and knowledge of these five injury patterns will aid surgeons in future management of these injuries and may improve treatment outcomes.

A new and reliable classification system for fractures of the navicular and associated injuries to the midfoot

AIMS

Fractures of the navicular can occur in isolation but, owing to the intimate anatomical and biomechanical relationships, are often associated with other injuries to the neighbouring bones and joints in the foot. As a result, they can lead to long-term morbidity and poor function. Our aim in this study was to identify patterns of injury in a new classification system of traumatic fractures of the navicular, with consideration being given to the commonly associated injuries to the midfoot.

PATIENTS AND METHODS

We undertook a retrospective review of 285 consecutive patients presenting over an eight- year period with a fracture of the navicular. Five common patterns of injury were identified and classified according to the radiological features. Type 1 fractures are dorsal avulsion injuries related to the capsule of the talonavicular joint. Type 2 fractures are isolated avulsion injuries to the tuberosity of the navicular. Type 3 fractures are a variant of tarsometatarsal fracture/dislocations creating instability of the medial ray. Type 4 fractures involve the body of the navicular with no associated injury to the lateral column and type 5 fractures occur in conjunction with disruption of the midtarsal joint with crushing of the medial or lateral, or both, columns of the foot.

RESULTS

In order to test the reliability and reproducibility of this new classification, a cohort of 30 patients with a fracture of the navicular were classified by six independent assessors at two separate times, six months apart. Interobserver reliability and intraobserver reproducibility both had substantial agreement, with kappa values of 0.80 and 0.72, respectively.

CONCLUSION

We propose a logical, all-inclusive, and mutually exclusive classification system for fractures of the navicular that gives associated injuries involving the lateral column due consideration. We have shown that this system is reliable and reproducible and have described the rationale for the subsequent treatment of each type. Cite this article: Bone Joint J 2018;100-B:176-82.

Translational repression by MSY4 inhibits spermatid differentiation in mice

In developing male germ cells, newly synthesized protamine mRNAs are stored for up to 7 days before translational activation. Translational repression of protamine 1 (Prm1) mRNA requires sequences present in its 3′ untranslated region (UTR) and substantial evidence suggests a role for the murine Y-box protein MSY4 in this process. To determine if MSY4 can mediate translational repression in vivo, we generated transgenic mice in which the temporal window of MSY4 expression was extended during spermatogenesis. Expression of MSY4 disrupted the normal completion of spermatogenesis and caused dominant sterility. Immunocytochemical analysis of several markers, including the protamines, indicated that MSY4 prevented normal activation of translation. mRNAs whose translation was inhibited contained at least one MSY4 RNA recognition site, suggesting sequence-dependent translational repression. Altered translational activation resulted in defective processing of protamine 2 and severe defects in sperm morphogenesis. These results suggest that MSY4 plays an active role in translational repression of several mRNAs in differentiating spermatids.

MSY2 and MSY4 bind a conserved sequence in the 3' untranslated region of protamine 1 mRNA in vitro and in vivo

Y-box proteins are major constituents of ribonucleoprotein particles (RNPs) which contain translationally silent mRNAs in gametic cells. We have recently shown that a sequence-specific RNA binding activity present in spermatogenic cells contains the two Y-box proteins MSY2 and MSY4. We show here that MSY2 and MSY4 bind a sequence, 5'-UCCAUCA-3', present in the 3' untranslated region of the translationally repressed protamine 1 (Prm1) mRNA. Using pre- and post-RNase T1-digested substrate RNAs, it was determined that MSY2 and MSY4 can bind an RNA of eight nucleotides containing the MSY2 and MSY4 binding site. Single nucleotide mutations in the sequence eliminated the binding of MSY2 and MSY4 in an electrophoretic mobility shift assay, and the resulting mutants failed to compete for binding in a competition assay. A consensus site of U(AC)C(A)CAU(C)CA(CU) (subscripts indicate nucleotides which do not disrupt YRS binding by MSY2 and MSY4), denoted the Y-box recognition site (YRS), was defined from this mutational analysis. These mutations in the YRS were further characterized in vivo using a novel application of the yeast three-hybrid system. Experiments with transgenic mice show that disruption of the YRS in vivo relieves Prm1-like repression of a reporter gene. The conservation of the RNA binding motifs among Y-box protein family members raises the possibility that other Y-box proteins may have previously unrecognized sequence-specific RNA binding activities.

A sequence-specific RNA binding complex expressed in murine germ cells contains MSY2 and MSY4

The protamine mRNAs are stored for up to 8 days as translationally repressed ribonucleoprotein particles during murine spermatogenesis. Translational repression of the protamine 1, Prm1, mRNA is controlled by sequences in its 3'-untranslated region (UTR). In this study we used the yeast three-hybrid system to clone Msy4, which encodes a novel member of the Y box family of nucleic acid binding proteins. MSY4 specifically binds to a site within the 5' most 37 nucleotides in the Prm1 3' UTR. Msy4 is highly expressed in the testis, and the protein is detected in the cytoplasm of germ cells in both the testis and the ovary, where repressed messages are stored. Analysis of a previously described 48/50-kDa binding activity in testis extracts by electrophoretic mobility shift assays and immunoprecipitation indicates the activity is composed of MSY4 and MSY2, another mouse Y box protein. Polysome analysis demonstrates MSY4 is associated with mRNPs, consistent with MSY4 having a role in storing repressed messages.

The effect of the human serum paraoxonase polymorphism is reversed with diazoxon, soman and sarin

Many organophosphorus compounds (OPs) are potent cholinesterase inhibitors, accounting for their use as insecticides and, unfortunately, also as nerve agents. Each year there are approximately 3 million pesticide poisonings world-wide resulting in 220,00 deaths. In 1990, there were 1.36 million kg of chlorpyrifos, 4.67 million kg of diazinon and 1.23 million kg of ethyl parathion manufactured in the USA (data supplied by the USEPA). In addition to exposure risks during pesticide manufacturing, distribution and use, there are risks associated with the major international effort aimed at destroying the arsenals of nerve agents, including soman and sarin. The United States has pledged to destroy approximately 25,000 tons of chemical agents by the end of the decade. The high density lipoprotein (HDL)-associated enzyme paraoxonase (PON1) contributes significantly to the detoxication of several OPs (Fig. 1). The insecticides parathion, chlorpyrifos and diazinon are bioactivated to potent cholinesterase inhibitors by cytochrome P-450 systems. The resulting toxic oxon forms can be hydrolysed by PON1, which also hydrolyses the nerve agents soman and sarin (Fig. 1). PON1 is polymorphic in human populations and different individuals also express widely different levels of this enzyme. The Arg192 (R192) PON1 isoform hydrolyses paraoxon rapidly, while the Gln192 (Q191) isoform hydrolyses paraoxon slowly. Both isoforms hydrolyse chlorpyrifos-oxon and phenylacetate at approximately the same rate. The role of PON1 in OP detoxication is physiologically significant. Injected PON1 protects against OP poisoning in rodent model systems and interspecies differences in PON1 activity correlate well with observed median lethal dose (LD50) values. We report here a simple enzyme analysis that provides a clear resolution of PON1 genotypes and phenotypes allowing for a reasonable assessment of an individual's probable susceptibility or resistance to a given OP, extending earlier studies on this system. We also show that the effect of the PON1 polymorphism is reversed for the hydrolysis of diazoxon, soman and especially sarin, thus changing the view of which PON1 isoform is considered to be protective.

Synthesis and storage in rat thyroid C-cells

Thyroid C-cells have the capacity to produce a variety of peptides, as do C-cell tumors. The cellular content of one such peptide, somatostatin, is restricted to a minority of C-cells in rat and human. We set out to clarify whether the synthesis of somatostatin is equally restricted and to study changes that occur in somatostatin synthesis with age. We used immunocytochemistry to localize somatostatin and calcitonin in conjunction with in situ hybridization, using digoxigenin-labeled oligoprobes to localize somatostatin and calcitonin mRNAs in serial sections of formalin-fixed, paraffin-embedded rat thyroid, and correlated peptide and mRNA content in individual cells. All C-cells synthesize and store calcitonin, and somatostatin synthesis, as shown by mRNA content, is limited to the subset of cells containing immunoreactive somatostatin. The numbers of C-cells in general and of the subset synthesizing somatostatin increase between juvenile and adult animals, but the somatostatin cells remain confined to a small area of the gland. These findings support the proposal that somatostatin production is not facultative, but that C-cells differentiate into two distinct subsets of cells, only one of which synthesizes and stores somatostatin.

Site of production of IGF1 in the normal and stimulated mouse thyroid

Insulin-like growth factor 1 (IGF1) has emerged as an essential factor in the follicular cell growth response in vitro to TSH, although its source within the thyroid in vivo is not clear. We have studied the localisation of IGF1 mRNA by in situ hybridization using digoxigenin labelled oligoprobes in tissue sections of mouse thyroid. Our results show that in the thyroid IGF1 mRNA is predominantly present in follicular cells and C cells rather than the stroma. Follicular cell levels are higher during postnatal thyroid growth and during the growth response to goitrogen administration, but decrease in the mature animal. This decrease in production is limited to the follicular cells, as IGF1 mRNA is still easily demonstrable in C cells and in the parathyroid. Immunocytochemistry for IGF1 peptide shows a weak and variable follicular cell content in both juvenile and mature mice, but a more uniform distribution during growth in response to a goitrogenic stimulus. These studies show that the follicular cells are the main source of IGF1 in the thyroid, and suggest that the role of IGF1 in follicular cell growth is as an autocrine factor.

Expression of calcitonin and somatostatin peptide and mRNA in medullary thyroid carcinoma

We have studied a series of 22 human medullary carcinomas (MCTs), both primary and metastatic, using immunocytochemistry (ICC) to localize calcitonin and somatostatin peptide and in situ hybridization (ISH) to localize calcitonin and somatostatin mRNA. All tumors were positive for calcitonin peptide with ICC, which often showed considerable intercellular heterogeneity, with many cells having undetectable levels of calcitonin. However, calcitonin mRNA localized by ISH was much more uniformly distributed, indicating that MCT tumor cells may retain the capacity to both synthesize and store calcitonin, whereas others lose their storage but not their synthetic capacity. Somatostatin peptide and mRNA were found in tumors from 15 patients. In contrast to the pattern seen with calcitonin, somatostatin mRNA and peptide were usually found in single scattered cells. When correlation was possible, the same cell showed positivity for somatostatin mRNA on ISH and positivity for somatostatin peptide on ICC. However, in one tumor many more cells were positive for mRNA than for peptide, suggesting that only a proportion of cells retained the ability to store the peptide. The variation in cellular content of immunoreactive calcitonin is interpreted as resulting from either an increased tumor growth rate or reduced ability to store peptide in a less differentiated tumor. With somatostatin there was good correlation between mRNA and peptide content, but it occurred in single widely scattered cells, most tumor cells being negative for both peptide and mRNA. It is suggested that somatostatin production might be associated with a reduction in the growth of the cell concerned, either through a differentiation step or through a direct effect of the hormone.(ABSTRACT TRUNCATED AT 250 WORDS)

Matrix metalloproteinase inhibitors containing a (carboxyalkyl)amino zinc ligand: modification of the P1 and P2' residues

Systematic modification of the presumed P1 side chain in a series of (carboxyalkyl)amino-based inhibitors of matrix metalloproteinases enabled identification of the 2-(1,3-dihydro-1,3-dioxo-2H-benz[f]isoindol-2-yl)ethyl group as a preferred substituent imparting potent inhibition of the enzymes collagenase and gelatinase. It was subsequently found that the P2'-P3' residues in this series could be replaced by small non-peptide residues, while maintaining inhibitory potency. The imide group in this series of compounds can undergo autocatalytic hydrolysis under neutral conditions.

Demonstration of mRNA using digoxigenin labelled oligonucleotide probes for in situ hybridisation in formamide free conditions

The value of formamide for use in in situ hybridisation (ISH) for the detection of mRNA, using either single or multi probe cocktails of digoxigenin labelled oligoprobes, was investigated. Three peptides with cell specific localisation in three separate tissues--calcitonin in the thyroid, epidermal growth factor (EGF) in the submaxillary gland, and insulin in the pancreas were studied. In each case localisation was confined to the appropriate cell type, but in the presence of formamide higher concentrations of probe and a longer development time were required. The abolition of formamide from the protocol for ISH makes the technique safer, cheaper, faster and more suitable for routine diagnostic use.

Oestrogen receptor protein and mRNA in adenocarcinoma of the uterine cervix

We have investigated the oestrogen receptor (ER) status of 20 cervical adenocarcinomas by immunocytochemistry for ER protein and non-isotopic in situ hybridisation for ER mRNA. Both methods, which are applicable to paraffin sections, were developed and validated in breast carcinomas with known ER content. Six cervical adenocarcinomas contained immunocytochemically demonstrable ER protein; all contained ER mRNA, but staining was less intense in poorly differentiated areas of four tumours. This disparity between protein and mRNA detection needs further investigation as does the possibility that oestrogens may play a role in the pathogenesis of cervical adenocarcinoma.

Antibiotic susceptibilities, serotypes and auxotypes of Neisseria gonorrhoeae isolated in New Zealand

OBJECTIVE

The aim of the study was to determine the distribution of auxotypes and serotypes and the prevalence of antibiotic resistance among New Zealand isolates of Neisseria gonorrhoeae.

MATERIALS AND METHODS

A total of 486 gonococci isolated in 1988 were auxotyped, serotyped, and tested for susceptibilities to ten antibiotics.

RESULTS

The gonococci were susceptible to all the antibiotics tested except penicillin and tetracycline. Eleven (2.2%) produced beta-lactamase, one (0.2%) showed chromosomal penicillin resistance, and 18 (3.7%) were resistant to a low-level of tetracycline. Most of the gonococci belonged to six auxotypes. The three predominant auxotypes were arginine-requiring (Arg-), non-requiring (NR), and arginine, hypoxanthine, uracil-requiring (AHU-). The majority of the isolates belonged to serogroup IB and to six serovars. The most prevalent serovars were IB-3 and IB-1. There was an association between penicillin susceptibility and auxotype or serovar among non-penicillinase producing N. gonorrhoeae (PPNG) isolates.

CONCLUSIONS

Antibiotic resistance, including penicillin resistance, remains uncommon among gonococci in New Zealand. Baselines have been established for future epidemiological studies using both auxotyping and serotyping.

Recent advances in the generation of chiral intermediates using enzymes

Different types of enzyme-catalyzed processes are reviewed, with particular regard to those procedures leading to the generation of chiral compounds of high optical purity. The main body of the review deals with hydrolyses and esterification as well as the reduction and oxidation of organic substrates. Other biotransformations of current and/or future importance in the synthesis of homochiral fine chemicals (such as the formation of carbon-carbon bonds using aldolases) are also discussed in some detail. Attention is drawn to current trends in the area and, to this end, a majority of the references are taken from journals published during the period April 1987 to September 1988.

Methicillin-resistant Staphylococcus aureus: an increasing threat in New Zealand hospitals

During the three years 1985 to 1987 an increasing number of methicillin-resistant Staphylococcus aureus (MRSA) strains were identified in New Zealand each year. A total of 66 strains of MRSA were identified among isolates received from 418 patients and health personnel. The majority (337/418, 80.6%) of the isolates were from two independent large outbreaks of MRSA. All strains of MRSA were sensitive to vancomycin, rifampicin and fusidic acid. An overseas origin, usually Australia, was identified for 48.4% of strains. The majority of isolates were from patients whose host defences had been breached. Postoperative and cutaneous wounds were the commonest sites of acquisition.

Association study between Alzheimer's disease and restriction fragment length polymorphisms at the human amyloid beta protein gene locus

Alzheimer's disease, an autosomal dominant disorder, is characterized by the presence of neurofibrillary tangles and senile extracellular plaques in the brain of affected individuals. An amyloid beta protein has been isolated from the core of these plaques, and the gene encoding this protein has been mapped to region q11.2 to q22.2 of chromosome 21. Independent linkage studies have shown that the locus responsible for familial Alzheimer's disease also maps to the long arm of chromosome 21. It is thus very tempting to speculate that a defect (or defects) of the amyloid beta protein gene is the cause of Alzheimer's disease. For this reason, we have done association studies between Alzheimer's disease and restriction fragment length polymorphisms of the amyloid beta protein gene locus. We report a study of six restriction fragment length polymorphisms at the human amyloid beta protein gene locus. Several haplotypes constitute very informative marker systems for this region of chromosome 21. One of the six polymorphisms, a 6.6/7.3 kb (kb = 10(3) base-pairs) EcoRI restriction fragment length polymorphism, is loosely associated with the presence of Alzheimer's disease in a population of 34 subjects.

Heat shocking as a useful adjunct to routine phage typing of Staphylococcus aureus

The heat shock technique (heating a culture at 55 degrees C for 3 min immediately before phage typing) has been used in our laboratory as an adjunct to routine phage typing for 2 years. This has enabled phage typing patterns to be determined on isolates otherwise recorded as untypable. The method is easily performed and standardized. Phage patterns were found to be reproducible and adequate discrimination was achieved. We found the technique provided significant information which was not available by conventional typing.

Observations on the kinetics of uranyl acetate and phosphotungstic acid staining of chromatin in thin sections for electron microscopy

When thin sections of spermatogenic chromatin are fixed with either glutaraldehyde alone or postfixed with osmium tetroxide (OsO4) and stained with uranyl acetate (UAc) for increasing times, even after as little as 1 min, stain uptake is proportional to section thickness. Greater UAc uptake is observed in chromatin fixed with glutaraldehyde only, but seen with postfixed chromatin. Lead citrate poststaining of chromatin fixed with either glutaraldehyde or postfixed with OsO4 increases UAc uptake by a factor of about 3. The staining of thin sections of spermatogenic chromatin with ethanolic phosphotungstic acid (PTA) shows a region where stain uptake is proportional to section thickness followed by a plateau. This staining pattern is seen in chromatin fixed with glutaraldehyde alone or postfixed with OsO4; similar levels for final PTA uptake are also observed. An increase in the resin content of embedded chromatin postfixed with OsO4 is proposed to explain the decrease and increase in the rate of migration of UAc and ethanolic PTA staining solutions, respectively.

Kinetics of lead citrate staining of thin sections for electron microscopy

The staining of thin sections with lead citrate shows an initial increase followed by a decrease much later; the rate of the initial increase and subsequent loss varies for different cellular components. The decrease eventually reaches a stable minimum. At this level electron scattering is less than that of unstained sections, demonstrating a loss of biological material. Lead citrate used as a poststain following uranyl acetate causes an increase in electron density that is independent of staining time over 1-30 min; this increase appears to depend only on the quantity of uranyl acetate already bound, implying that the lead binds predominantly to the uranyl acetate.

Electron microscopic observations on the development and cytochemistry of the large granule complexes in chicken erythrocyte nuclei

Large granule complexes are structures found in a small percentage of chicken erythrocyte nuclei when observed in ultra-thin sections in the electron microscope. They consist of an amorphous region associated with a number of large (approximately 30 min) granules. We have shown, by a novel use of phenylhydrazine to synchronize populations of chicken erythrocytes in vivo, that large granule complexes do not occur in the nuclei until the cells have reached one-third to one-half of their normal intravascular lifespan. The mature large granule complexes are formed by aggregation of pre-existing fibrillar, granular and amorphous material, and their presence is correlated with the presence of another ultrastructural feature of the nucleus, the so-called “filled cavities' in the chromatin. Digestion of ultra-thin sections of erythrocytes embedded in the hydrophilic resin glycol methacrylate (GMA) has shown that the major component of the amorphous region is a rather acidic protein that is not haemoglobin, the most abundant protein in the erythrocyte. The large granules also contain protein and, almost certainly, RNA. The problems encountered in reaching this conclusion have emphasized the lack of unambiguous cytochemical tests for use on ultra-thin sections. We have shown that the large granule complex differs in many respects from the nucleolus in the erythrocyte series, even though the two organelles have certain superficial similarities such as their overall dimensions and the presence of granular and fibrillar regions. The most likely function of the large granule complex is as a repository for material, including RNA, the processing of which has ceased in the inactivated erythrocyte nucleus.

A critical evaluation of Bernhard's EDTA regressive staining technique for RNA

The EDTA regressive staining procedure to detect RNA (Bernhard's technique) is based on the proposition that after staining ultrathin sections with uranyl the stain is preferentially removed from DNA rather than RNA by the action of the chelating agent EDTA. Whilst attempting to use the EDTA regressive staining procedure to detect the presence of RNA in the large granule complexes of chicken erythrocyte nuclei, certain anomalous staining patterns were observed in the chromatin of these nuclei. Essentially, these were that the edges of condensed chromatin bodies stained positively for RNA even though this molecule is known not to be present there in significant quantities. The staining patterns suggested that chromatin was retaining its stain in a manner expected of RNA but not DNA as a consequence of EDTA-containing species failing to pass freely through the section. This hypothesis was tested by carrying out the EDTA procedure on embedded specimens of a DNA-containing virus, simian virus 40 (SV40), small enough not to be exposed at the surface of the section. In this way it has been shown that virus particles completely surrounded by resin destain so much more slowly than chromatin, which is accessible at the surface of the section, that without any other information it would be concluded that the viruses contained RNA, not DNA. This apparently anomalous result arises because the difficulties encountered by stain or EDTA molecules in passing through a plastic section were not appreciated at the time of the initial publication of the technique. The observations are discussed in the light of recent knowledge that has been gained on the kinetics of staining by measuring the electron-scattering densities of stained sections, similar measurements having been made on sections stained by Bernhard's technique. A model for the mechanism of the EDTA regressive staining technique consistent with the experimental observations is proposed and the conditions under which Bernhard's staining procedure retains its specificity are defined. Briefly, these conditions are that: (a) the sections be stained for only a short period with uranyl before treating them with EDTA even though such brief staining is undesirable for quantitative measurements of stain uptake into biological material; and (b) that sections stained in lead only be compared as controls with sections stained by Bernhard's technique so that any specificity of lead for sub-cellular components is not confused with a positive indication of the presence of RNA. Unless these conditions are fulfilled, results obtained by the use of the regressive staining technique may be highly misleading.

Jet expulsion of cellular contents from rad cells during photodynamic hemolysis

When red cells are incubated in the dark in the presence of the dye Rose Bengal and subsequently irradiated with visible light, they hemolyze. Under certain conditions some of the hemoglobin is expelled in the form of a convective jet and appears as a transient cloud beside the cell. Elastic contraction of the membrane is not a sufficient driving force for the jet. A plausible mechanism (an osmotic "pump") is presented.

Three-dimensional reconstruction of the chromatin bodies in the nuclei of mature erythrocytes from the newt Triturus cristatus: the number of nuclear envelope-attachment sites

The arrangement of the chromatin bodies in the interphase nuclei of 6 erythrocytes has been investigated by means of 3-dimensional reconstruction from electron micrographs of serial sections. When the borders of chromatin bodies are marked on the surface of each model, discrete areas of chromatin in contact with the nuclear envelope are revealed. The number of these areas in approximately equal to the number of chromosomes in the diploid set. The data suggest that each chromatin body corresponds to a condensed interphase chromosome and that each chromosome is attached to one discrete site on the nuclear envelope. The data are insufficient to show whether or not the condensed chromosomes are arranged in any orderly pattern in these nuclei.

Electron-microscope observations on cell nuclei in various tissues of a teleost fish: the nucleolus-associated monolayer of chromatin structural units

Observations on stain uptake by thin sections through condensed interphase chromosomes in cells from epithelial and muscle tissue in kidney and intestine, and also in fibroblasts, show a distribution into DNA-rich and DNA-poor phases similar to that already described in cells from the connective tissue blood. In all the nuclei the nucleolus, when adjacent to the nuclear envelope, is separated from the inner membrane by a monolayer of chromatin structural units, similar to the monolayer enclosed on both sides by nuclear envelope, previously described in a wide variety of organisms. The data provide further support for the hypothesis that the condensed interphase chromosomes in eukaryotes are characterized by essentially similar structural units folded to form similar patterns. This hypothesis, regarding the higher order units, is consistent with data of others which show that histones and DNA fold to form similar repeating subunits in chromatin, irrespective of the base sequence in the DNA and the origin of the histones.

Electron microscopy of interphase chromosomes in situ; binding of permanganate to chicken erythrocytes

From quantitative electron-microscope observations on the binding of permanganate to regions of erythrocytes and reticulocytes of known chemical composition, it is concluded that KMnO4, like phosphotungstic acid (PTA), binds preferentially to sites on proteins. Compared with PTA, KMnO4 binding exhibits less anomalous behaviour. The data support the hypothesis previously put forward that the 2 regions, or phases, in condensed chromatin differ in both molecular composition and concentration. The increase in binding to protein which occurs during nuclear haemolysis is interpreted in terms of protein-protein interaction in the chromatin of the intact cell.

Light- and electron-microscope observations on certain leukocytes in a teleost fish and a comparison of the envelope-limited monolayers of chromatin structural units in different species

Previously it was shown that the nuclear envelope-limited sheets of chromatin, monolayers of nucleoprotein structural units, are present in blood cells from 4 classes of vertebrates. Now we show that sheets of similar width are present in certain leukocytes of a fifth class, a teleost fish. We describe the fine structure of leukocytes in peripheral blood and in the main haematopoietic organ, kidney. We also examined the granulocytes of connective tissue in intestine. By May-Grunwald-Giemsa staining and electron microscopy heterophilic granulocytes, cosinophils but no basophils could be recognized in peripheral blood and kidney. Problems in classification of the cells are discussed. In one group (A) of 5 fish, sheets occurred at a frequency of roughly 1% in heterophilic (type 1) granulocytes and lymphocytes from peripheral blood. No sheets were found in a second group (B) of 5 fish. Kidney and intestine were examined in some fish from both groups and no sheets were present. In an atypical group (C) sheets were found in the eosinophilic (type 2) granulocytes from peripheral blood of one fish and in lymphocytes from connective tissue of intestine in another. Sheets were usually associated with nuclei of irregular shape and their width averaged 36 nm. We tabulate data from other workers on occurence and width of sheets. They are found in all the main classes of tissue in mammals, namely blood and other connective tissues, in epithelial, nervous, germinal tissue and muscle, as well as in invertebrate and certain plants. Their nearly constant width, average value 35 nm, provides very convincing evidence for the hypothesis that the molecules of DNA and protein are organized into the same fundamental structural units, irrespective of species. We discuss the variable incidence of sheets among different cell types and the factors which might determine this.

Ultrastructural and biochemical observations on interphase nuclei isolated from chicken erythrocytes

Adult hen erythrocyte nuclei are isolated from cells or haemolysed in situ by acting on the plasma membrane with rotating knives or with non-ionic detergents. When the isolation medium contains magnesium ions (1 mM), sucrose (0-4 M) and Tris buffer (0.01 M, pH 7-5) called SMTOG (see text), the ultrastructure in thin sections through the condensed chromatin bodies, after staining with either uranyl-lead or phosphotungstic acid (PTA), is similar to that found in the intact cell. Hence it can be concluded that the 2 phases which comprise chromatin, the o- and e-phase, survive nuclear isolation. These are so called because the structural units in chromatin are arranged at the surface of the nucleus into one or more layers and give rise to oddly (o) and evenly (e) numbered bands. The 0-phase is also largely retained after extensive washing in 0-07 M NaC1 as shown by electron microscopy and biochemical measurements; only 6% of the total nuclear protein is removed, a value small compared with the fractional amount of the chromatin protein calculated to lie in the o-phase, about 70%. After extensive washing in saline-EDTA there are structural changes in chromatin, but biochemical data show that the molecules in the o-phase are also largely retained; loss of protein amounts to between 5 and 11%. These data suggest that the o-phase is a structural component of the chromatin bodies. They support the hypothesis that condensed chromatin is formed by folding superunit threads. These units consist of a central thread-like element about 17 nm diameter which stains preferentially with uranyl-lead and forms the e-phase, with an outer cylindrical shell forming the o-phase of total diameter about 28nm. The 5–10% proteins removed by salt washes are located exclusively in a particulate component, quite likely the chromatin. They have been examined by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis. There are about 10 or more protein species, ranging in molecular weight from 21000 upwards. The groups of large granules previously found in the nuclear sap of intact erythrocytes are shown to be associated with an amorphous or finely fibrillar body.

Electron-Microscope Observations on the Organization of the Nucleus in Chicken Erythrocytes and a Superunit Thread Hypothesis for Chromosome Structure

Previously it was shown that when condensed chromatin from several different types of cell is stained with uranyl-lead and examined in thin sections in the electron microscope, the stain is distributed into a dot-dash pattern arising from threads, with lesser-staining intermediate areas. We now show that when a section through chicken erythrocyte chromatin is stained with ethanolic phosphotungstic acid (PTA) the stain distribution is homogeneous. This shows that the lesser-staining regions after uranyl-lead, cannot be an overlap artifact. We conclude that the stains and hence the molecules in chromatin are distributed between 2 phases, an o- and an e-phase, so called because the structural units in chromatin are arranged in an orderly way at the surface of the nucleus and give rise to oddly (o) and evenly (e) numbered bands. Measurements of electron density per unit thickness, proportional to the number of stain molecules per unit volume, are made in thin sections through erythrocytes and reticulocytes from adult hen, 4-day-old chicks and 17-day embryos. The results indicate differences in the packing of the molecules in chromatin and further show that the e-phase is quite likely to have a higher DNA to protein ratio than the o-phase. After uranyl-lead stain the visibility of the dot-dash pattern in cells from adult hen is relatively low due, we propose, to closer packing. In micrographs through condensed chromatin treated with uranyl-lead the eye selects out only the densely stained dots and dashes, width 17 nm. When erythrocyte chromatin is partially or completely disrupted in various ways, threads 25-30 nm then become visible. We propose that condensed chromatin in intact cells contains structural units which consist of a central element, width 17 nm previously referred to as the unit thread, forming the e-phase, surrounded by a cylindrical shell forming the o-phase. This socalled superunit thread is similar in width, about 25-30 nm, to that reported by other workers in preparations of chromosomes spread on water surfaces. The hypothesis therefore helps explain what appeared to be discrepancies in thread dimensions. Certain other ultrastructural features of erythrocyte nuclei are also reported which are either pertinent to the general aim of this study, namely the way in which nucleoproteins fold up in chromosomes, or to biochemical studies, to be reported shortly, in which attempts are made to locate the proteins removed from isolated erythrocyte nuclei during subsequent washing in salt solutions.

Observations on the Origin and Significance of the Nuclear Envelope-Limited Monolayers of Chromatin Unit Threads associated with the Cell Nucleus

Monolayers of chromatin structural units about 33.0 nm in width enclosed on both sides by extensions of the nuclear envelope, called sheets, and located either in the cytoplasm (c. .n. .c type), or within the nucleus (c. .n. .n type), are common in cultured cells of Burkitt's lymphoma. The sheets are absent from mitotic cells except at telophase where, unlike interphase, type c. .n. .n is more numerous than c. .n. .c. The degree of nuclear asymmetry is defined in terms of the increase in enclosing membranes over that required to enclose the same area in a circular configuration. The percentage number (Ps) of cells with nucleus-associated sheets averaged over all stages in the cell cycle, increases with cell viability and with nuclear asymmetry. However, during the cycle there is a marked diminution in Ps during the S-phase of DNA synthesis when nuclear asymmetry itself does not change. Hence, it is suggested, and data on other cell types support the hypothesis, that nuclear asymmetry is a necessary but not sufficient factor in causing sheets to form. Microtubules are present within the cytoplasm and their morphological arrangement suggests a role in determining nuclear asymmetry. Treatment with a microtubule depolymerizing agent, colcemid, does not alter either the existing nuclear asymmetry or Ps, but when cells are treated early in S-phase the reappearance of sheets in the G2 phase of the cell cycle is considerably delayed. The reappearance takes place when the microtubules are still depolymerized. It is suggested that synthesis of membrane in excess of what is needed to enclose a sphere results in nuclear asymmetry and associated membrane-enclosed monolayers, the resulting nuclear conformation, including the distribution of membrane between types c. .n. .n and c. .n. .c, depending on what is energetically favoured. No biochemical function has yet been assigned to sheets.

The Haemoglobin in the Condensed Chromatin of Mature Amphibian Erythrocytes: A Further Study

The condensed chromatin in mature nucleated erythrocytes is surrounded by nuclear haemoglobin at a concentration about equal to that in the cytoplasm. New measurements employing improved fixation, glutaraldehyde instead of OsO4, and microspectrophotometric analyses instead of photographic photometry at one wavelength, show that previously reported values for the content of haemoglobin in the mass of the chromatin in Triturus cristatus, 45-50%, were far too high. In the condensed chromatin of 3 species of amphibia the concentrations of intrachromatin haemoglobin relative to the cytoplasm are 10% (Triturus cristatus), 10% (Necturus maculosa) and 8% (Amphiuma tridactylum). It is concluded that haemoglobin is only a minor component of chromatin, and this result is discussed in relation to the condensation of erythrocyte chromatin and observations on its ultrastructure.

Electron-Microscope Observations on the Structure of Condensed Chromatin: Evidence for Orderly Arrays of Unit Threads on the Surface of Chicken Erythrocyte Nuclei

A unit thread has been identified by electron microscopy as the common structural element in the condensed chromatin of a variety of cell nuclei. From the previous studies of thin sections normal to the nuclear envelope it was concluded that the unit thread, of diameter about 17 nm but varying somewhat depending on fixation, packed with spacings of about 28 nm on the surface of the nucleus to form one or more layers. Thin sections tangential to the nuclear envelope, described in this paper, reveal directly the degree of order within the surface layer; there are small areas or patches in which the units are regularly arranged. Units are also orderly arranged around the pores in the nuclear envelope. Unit threads are less easily visible in electron micrographs of mature erythrocytes than at earlier stages of development but the clarity with which they can be seen is increased by a brief treatment prior to fixation with sodium citrate.

Electron-microscope observations on the organization of heterochromatin in certain cells

Electron micrographs of sections through the heterochromatin (condensed chromosomes) of erythrocytes from chicken and lamprey reveal alternate equispaced electron-dense and relatively less dense bands lying adjacent and parallel to, and extending considerable distances along, the nuclear envelope. Frequently a triple-structured band (average half-width 183 Å), consisting of a less dense band, a dense band (width 130-170 Å), and a second less dense band is encountered; sometimes there are many (10-12) bands. The dense bands have a variable structure; they may appear continuous or consist of equispaced granules about 220 Å apart, which sometimes have a less dense centre. Similar but shorter dark bands and granules appear throughout the chromatin. Tilting the section in the microscope causes the micrographs to change, bands and granules disappearing and reappearing elsewhere, demonstrating that the images are produced by superposition of structures small in dimensions compared with the thickness of the section. Tilting about an axis normal to the band may resolve it into granules. These data indicate that the heterochromatin contains a well-defined structural unit which can form ordered regions, namely layers in contact with the nuclear envelope. The possibility of errors in interpreting the substructure of the bands due to complexity of superposition effects is stressed. The simplest hypothesis to account for the images is that the units are microtubes of outside diameter 130-170 Å, perhaps microhelices formed by coiling DNA with protein, spaced apart equally, perhaps by spacing elements. Microtubes parallel to the optic axis would appear as hollow granules, several one above another in a plane parallel to the axis appearing as a dark band. A similar triple-structured band of average half-width 224 Å is found in cells from newt spleen, lymphocytes, polychromatophil erythroblasts, mature erythrocytes, basophilic granulocytes, reticular cells and macrophages. A survey of published micrographs shows a similar triple-structured band of average half-width 212 Å to be a common feature of many cell types. A triple-structured band probably gives rise to the sheets of chromatin, now shown to have a similar triple-layered structure, limited on both sides by nuclear envelope, previously found attached to interphase nuclei and mitotic chromosomes in certain polychromatic erythroblasts from the newt. The effects of tilting the section were studied on objects of known geometry, membranes and cytoplasmic microtubules.

Light- and Electron-Microscope Studies on the Spleen of the Newt Triturus Cristatus: The Fine Structure of Erythropoietic Cells

The stages of erythrocyte maturation were identified in spleen smears stained with May-Grünwald-Giemsa. The fine structure of sectioned cells from about the basophilic erythroblast stage onwards was investigated in the electron microscope and serial I-µ sections were examined by microspectrophotometry to ascertain haemoglobin content. The nuclei of basophilic erythroblasts contain large and small blocks of chromatin as well as light-staining zones of unknown composition and ill-defined structure: the nuclear sap contains numerous interchromatin granules, about 400 Å in diameter. During maturation the small blocks of chromatin aggregate and the nuclear light-staining zones tend to disappear, as do the interchromatin granules. Storage lysosomes occur in the basophilic and early polychromatic erythroblasts and during subsequent maturation these lysosomes are probably involved in the degradation of mitochondria. The changes in distribution of ribosomes in cells at the later stages of maturation have been investigated by counting the numbers of single ribosomes and polysomes seen in electron micrographs. During erythropoiesis the ratio of the amount of fibrillar material to the amount of granular material in the nucleolus increases; in the mature erythrocyte the nucleolus consists almost exclusively of fine fibrillar material.

Electron- and Light-Microscope Observations on the Spleen of the Newt Triturus Cristatus: The Surface Topography of the Mitotic Chromosomes

In polychromatophil erythroblasts, and in cells containing little or no haemoglobin, the surfaces of the mitotic chromosomes frequently bear finger-like projections averaging about 0.1 µ in diameter. Both the mitotic and interphase chromosomes in polychromatophil erythroblasts from some newts bear, in addition, extensive sheets of chromatin, about 315-465 Å thick, depending on fixation, bounded on each side by nuclear envelope-like fragments. The remarkably constant width of the sheets in all cells indicates that chromosomes contain a constructional unit of fixed dimensions. This unit may have general significance, since other workers have found envelope-limited sheets of similar dimensions in one plant and several animal species. An hypothesis concerning the construction of chromosomes is discussed. It seeks to relate the thickness of the sheets of chromatin to the average diameter of the majority of the finger-like processes.

The large intranuclear granules, 400 Å in diameter, in polychromatophil erythroblasts survive in polysome-like configurations in dividing cells.