Alterations in the structure of the EBV nuclear antigen, EBNA1, in epithelial cell tumours

The EBV nuclear antigen, EBNA1, is the only viral protein consistently expressed in all virus-infected cells. It is required in trans for viral replication, maintenance of EBV extrachromosomal episomes, and transcriptional transactivation in latently-infected B-cells. It binds RNA suggestive of a regulatory role in post-transcriptional events and in transgenic mice, it is tumorigenic. In RNase protection studies relating to the EBV-associated tumour, nasopharyngeal carcinoma (NPC), we show that a C-terminal EBNA1 RNA probe from the prototype B95-8 marmoset strain can protect its own mRNA from enzymatic digestion, but does not fully protect EBNA1 mRNA from NPC cells. This finding is consistent with changes in the coding region for the antigen. We thus determined the sequences of EBNA1 genes derived from an NPC xenograft and numerous patient biopsies and identified a number of mutations in the gene in these human cells, relative to B95-8. Many of the nucleotide changes would lead to non-conservative amino acid alterations in apparently functionally significant regions of the protein. We show that although some of the mutations lie in regions designated as critical to DNA binding, they have negligible effect on this property of EBNA1. The basic regions in EBNA1 that may bind to RNA, at least in vitro, are exempt from mutation. Thus, unless the alterations are 'silent', which for such a critical viral function seems unlikely, they may relate to as yet unmapped viral activities, such as a role in tumorigenesis and the ability of EBNA1 to evade the cellular immune system, or be associated with the ability of the antigen to regulate gene transcription.

Childbirth in rural areas: maternal deaths, village deliveries and obstetric service use

We explored village maternal deaths in an area of the East Sepik Province of Papua New Guinea where most women delivered at home. Postpartum haemorrhage, retained placenta and puerperal sepsis were common causes of death. Follow-up of a group of pregnant women showed that abnormal labour was frequent. 24% of multigravidae (95% CI 17-33) reported a labour that lasted longer than 24 hours. In 9% of all births (95% CI 5-15) the third stage lasted longer than one hour, or products were retained. Despite a high proportion of obstetric complications in apparently low-risk villages births, few women attend a health facility for delivery. Health centre attenders were a relatively privileged group. Some hospital users complained about staff attitudes. A poor reputation means that women are less likely to use health services for delivery. Providers need to improve the acceptability of the care provided, and communities should be encouraged to help with transport for their women to go to a health facility when they are in labour.

An algorithm to estimate age in women during their childbearing years

Estimating age in women living in rural areas of Papua New Guinea can be inaccurate and subject to observer bias. Parity is often used, but this means that survey results cannot be used to examine the effect of childbearing on nutrition. We describe a method for estimating age in women independent of their parity developed during studies of women's health in the Wosera Subdistrict of Papua New Guinea. The tool, appropriately modified, may be useful to others conducting surveys requiring an estimate of maternal age.

Birthweight and gestation of village deliveries in Papua New Guinea

This study investigates the birthweight, gestational age, and body proportions of home births in a malarious area of Papua New Guinea. A population based cohort of pregnant women was followed longitudinally through pregnancy. Within the first few days of birth anthropometric measures were taken and a gestational age assessment made. Of the 121 live singleton infants, forty per cent were low birthweight and the preterm rate was 4 per cent. Infants appeared to be proportionally growth retarded. Low birthweight was associated with short maternal stature, and preterm delivery maternal illness. Mean birthweight derived from hospital statistics of babies born to women from the same area was higher than the mean derived from this population based study.

Avoiding neonatal death: an intervention study of umbilical cord care

During a study of pregnancy in a poor rural tropical area, a high prevalence of neonatal fever and umbilical cord infection was detected. Interim analysis showed that this was associated with subsequent development of neonatal sepsis. Therefore an intervention was introduced in two stages. In the first stage, acriflavine spirit and new razor blades were supplied to mothers, along with instructions for use, through antenatal clinics. In the second stage, when excessive cord bleeding was reported, umbilical cord clamps were added to the pack. The packs were associated with reduction of serious morbidity in the neonatal period. The study demonstrates the importance of umbilical cord care in the aetiology of life threatening neonatal morbidity in village births in a developing country and the effect of a simple intervention in reducing morbid episodes in the neonate.

Attenuation of nursing-related ovarian suppression and high fertility in well-nourished, intensively breast-feeding Amele women of lowland Papua New Guinea

Intense, sustained nursing lengthens inter-birth intervals and is causally linked with low natural fertility. However, in traditional settings, the effects of such nursing on fertility are difficult to disentangle from those of nutrition. Results from a prospective, direct observational study of reproductive function in well-nourished Amele women who nurse intensively and persistently but who also have high fertility are here presented. Endocrine measures show that ovarian activity resumes by median 11.0 months postpartum. Median duration of postpartum amenorrhoea is 11.3 months, time to next conception is 19.0 months, and the inter-birth interval is 28.0 months. Average life time fertility is 6.8. High fertility in Amele women is due both to refractoriness of reproductive function to suckling stimuli, and to maintenance of equivalent age-specific fertility rates across the reproductive life span.

A simple and efficient method for site-directed mutagenesis with double-stranded plasmid DNA

A general, simple and efficient method for preparing site-specific mutations in double-stranded plasmid DNA without the need for special plasmids, bacterial strains or reagents is described. Only one synthetic oligonucleotide for each mutation is required, subcloning is unnecessary and a high efficiency of mutation (58-97%) was obtained. If two synthetic oligonucleotide primers are used, two separate mutations can be simultaneously created in a single reaction tube.

DNA damage in non-proliferating cells subjected to ionizing irradiation at high or low dose rates

Ionizing radiation damage to the genome of a non-cycling mammalian cell is analyzed using continuous time Markov chains. Immediate damage induced by the radiation is modeled as a batch Poisson arrival process of DNA double strand breaks (DSBs). Different kinds of radiation, for example gamma rays or alpha particles, have different batch probabilities. Enzymatic modulation of the immediate damage is modeled as a Markov process similar to the processes described by the master equation of stochastic chemical kinetics. An illustrative example is the restitution/complete exchange model, which postulates that radiation induced DSBs can subsequently either undergo enzymatically mediated repair (restitution) or can participate pairwise in chromosome exchanges, some of which make irremediable lesions such as dicentric chromosome aberrations. One may have rapid irradiation followed by enzymatic DSB processing or have prolonged irradiation with both DSB arrival and enzymatic DSB processing continuing throughout the irradiation period. A complete solution of the Markov chain is known for the case that the exchange rate constant is negligible so that no irremediable chromosome lesions are produced and DSBs are the only damage to the genome. Using PDEs for generating functions, a perturbation calculation is made assuming the exchange rate constant is small compared to the repair rate constant. Some non-perturbative results applicable to very prolonged irradiation are also obtained using matrix methods: Perron-Frobenius theory, variational methods and numerical approximations of eigenvalues. Applications to experimental results on expected values, variances and statistical distributions of DNA lesions are briefly outlined. Continuous time Markov chain models are the most systematic of those current radiation damage models which treat DSB-DSB interactions within the cell nucleus as homogeneous (e.g. ignore diffusion limitations). They contain most other homogeneous models as special cases, limiting cases or approximations. However, applying the continuous time Markov chain models to studying spatial dependence of DSB interactions, which is generally believed to be very important in some situations, presents difficulties.

[Computerized image analysis for retinal nerve fiber layer: a preliminary report]

The principle and method for analysing the white-black photographs of retinal nerve fiber layer (RNFL) by using the technique of computerized image analysis were introduced. An objective and quantitative result of RNFL on the white-black photograph was initially obtained, and using the technique of fulse colour, each of the RNFL could be showed, which seem to have more advantages than observing RNFL on a white-black photograph.

A new method for estimating the acoustic attenuation coefficient of tissue from reflected ultrasonic signals

The parameter characterizing the acoustic attenuation in soft tissues is an indicator of tissue state. A method which features autoregressive deconvolution and spectral smoothing is proposed for estimation of the parameter from ultrasonic signals reflected from the tissue. The results of simulation and of processing actual liver data show that the standard deviation of the estimation is approximately halved by this method, compared to the traditional spectral differences method.

Lactation and birth spacing in highland New Guinea

The effects of infant suckling patterns on the post-partum resumption of ovulation and on birth-spacing are investigated among the Gainj of highland New Guinea. Based on hormonal evidence, the median duration of lactational anovulation is 20·4 months, accounting for about 75% of the median interval between live birth and next successful conception (i.e. resulting in live birth). Throughout lactation, suckling episodes are short and frequent, the interval changing slowly over time, from 24 minutes in newborns to 80 minutes in 3-year olds. Maternal serum prolactin concentrations decline in parallel with the changes in suckling patterns, approaching the level observed in non-nursing women by about 24 months post-partum. A path analysis indicates that the interval between suckling episodes is the principal determinant of maternal prolactin concentration, with time since parturition affecting prolactin secretion only in so far as it affects suckling frequency. The extremely prolonged contraceptive effect of breast-feeding in this population thus appears to be due to (i) a slow decline in suckling frequency with time since parturition and (ii) absence of a decline over time in hypothalamic–pituitary responsiveness to the suckling stimulus.

Developmental changes in brain glycoproteins

During the postnatal development of rat brain there are large increases in the concentration of brain glycoproteins. Between 1 and 30 days the greatest changes (70-100%) take place in the levels of glycoprotein mannose, galactose and glucosamine, accompanied by smaller increases (35-55%) in sialic acid and fucose. By 30 days of age levels of brain glycoproteins are within 5% of the adult values. Analyses of the molecular size and composition of glycopeptides prepared from brains of 1- and 30-day-old rats lead to the conclusion that during postnatal brain development there is a preferential synthesis of a distinct population of glycoproteins containing oligosaccharides consisting predominantly of glucosamine, mannose and galactose. These oligosaccharides therefore have a large 'core' segment and a relative deficiency of the characteristically terminal sugars, fucose and sialic acid. In very young rat brain there are also large amounts of a metabolically stable form of glycogen or limit dextrin which accompanies the glycopeptides through the usual methods involved in their preparation from brain glycoproteins. The concentration of this glucose polymer decreases by 93% within 30 days after birth, but its presence even in adult brain is a likely explanation for the numerous reports of small amounts of glucose in brain glycopeptides and glycoproteins.

Distribution and metabolism of glycoproteins and glycosaminoglycans in subcellular fractions of brain

The distribution, carbohydrate composition, and metabolism of glycoproteins have been studied in mitochondria, microsomes, axons, and whole rat brain, as well as in various synaptosomal subfractions, including the soluble protein, mitochondria, and synaptic membranes. Approximately 90% of the brain glycoproteins occur in the particulate fraction, and they are present in particularly high amounts in synaptic and microsomal membranes, where the concentration of glycoprotein carbohydrate is 2-3% of the lipid-free dry weight. Treatment of purified synaptic membranes with 0.2% Triton X-100 extracted 70% of the glycoprotein carbohydrate but only 35% of the lipid-free protein residue, and the resulting synaptic membrane subfractions differed significantly in carbohydrate composition. The glycoproteins which are not extracted by Triton X-100 also have a more rapid turnover, as indicated by the 80-155% higher specific activity of hexosamine and sialic acid 1 day after labeling with [3H]glucosamine in vivo. The specific activity of sialic acid in the synaptosomal soluble glycoproteins 2 hr after labeling was greater than 100 times that of the synaptosomal particulate fraction, whereas the difference in hexosamine specific activity in these two fractions was only twofold, and by 22 hr there was little or no difference in the specific activities of sialic acid and hexosamine in synaptosomal soluble as compared to membrane glycoproteins. These data indicate that sialic acid may be added locally to synaptosomal soluble glycoproteins before there is significant labeling of nerve ending glycoproteins by axoplasmic transport. Fifty to sixty percent of the hyaluronic acid and heparan sulfate of brain is located in the various membranes comprising the microsomal fraction, whereas half of the chondroitin sulfate is soluble and only one-third is in microsomal membranes. When microsomes are subfractionated on a discontinuous density gradient over half of the hyaluronic acid and chondroitin sulfate are found in membranes with a density less than that of 0.5 M sucrose (representing a six- to sevenfold enrichment over their concentrations in the membranes applied to the gradient), whereas half of the heparan sulfate is present in membranes with a density greater than that of 0.8 M.