Development of an infection prevention and control pathway to facilitate high-throughput cataract surgery in Scotland

INTRODUCTION

Cataract surgery offers significant improvement to quality of life for patients with cataracts. However, there are growing waiting lists and challenges in providing this type of surgery in a timely manner. Feedback from stakeholders had previously indicated infection prevention and control (IPC) as a potential barrier to high-throughput surgery. Antimicrobial Resistance and Healthcare Associated Infection Scotland was asked to support the implementation of high-throughput cataract surgery aimed at addressing these challenges.

AIM

To develop an IPC pathway to facilitate high-throughput surgery. This would be based on best practice, and would address any barriers identified by stakeholders.

METHODS

A short life working group with input from key stakeholders, including clinical teams, was established. A rapid literature review was also undertaken.

RESULTS

An agreed patient pathway was developed, with the aim of helping to facilitate high-throughput surgery. Pre-, intra- and postoperative phases were considered. Where literature was unavailable, expert/consensus opinion was utilized. Facilities for high-throughput surgery were also considered, including the Jack and Jill theatre arrangement which lends itself well to this concept.

CONCLUSION

Through collaboration with stakeholders, an IPC pathway was developed to facilitate high-throughput cataract surgery and address any potential IPC barriers to implementation. The process and the output described could be utilized to develop similar pathways for other surgeries that lend themselves well to high throughput, improving quality of life for patients and reducing waiting times. This study highlights the importance of establishing surveillance for postoperative endophthalmitis following implementation.

Attack rate and prey preference of Lasioseius subterraneous and Protogamasellus mica on four nematode species

Plant parasitic nematodes are common and important global pests, causing over US$150 billion in crop losses across the agricultural sector worldwide. Meloidogyne javanica and Pratylenchus zeae are two of the most damaging plant-parasitic nematodes and there are limited options for their control. We evaluated the potential of a large (Lasioseius subterraneous) and a small (Protogamasellus mica) mesostigmatan mite as biological control agents of plant-parasitic nematodes. We tested the attack rate and reproductive potential of these two mite species on four nematode species: M. javanica (eggs), Pra. zeae (adults) and two microbivorous nematodes, Mesorhabditis sp. and Aphelenchus avenae (adults for both species). Each mite/nematode combination (1 mite:100 nematodes) was tested in six replicate arenas. In a separate trial, each mite species was presented with 50 A. avenae and 50 Pra. zeae in the same arena to determine prey preference. Both mite species significantly reduced the abundance of all nematode species used in the trials when compared to nematode-only controls. Lasioseius subterraneous consumed all available M. javanica eggs within 72 h. The larger mite had a significantly higher overall attack rate than the smaller mite, each consuming an average of 96 and 72 nematodes, respectively, within 72 h. However, both mites had a similar reproductive rate. Protogamasellus mica displayed a positive preference towards the plant parasitic nematode Pra. zeae over the fungal feeding A. avenae whereas L. subterraneous did not display a prey preference. Our results highlight the potential of these two predators to control plant parasitic nematodes, although further trials under field conditions are needed.

Eco-hydrological requirements of dune slack vegetation and the implications of climate change

Dune slacks are a seasonal coastal wetland habitat, whose plant assemblages and soil properties are strongly linked to a fluctuating water table. Climate change is predicted to cause major shifts in sand dune hydrological regimes, yet we know remarkably little about the tolerance of these communities to change, and their precise hydrological requirements are poorly quantified. Dune slack vegetation and soils were sampled within five vegetation types across four west coast UK sites. Relationships between vegetation assemblages, and parameters of soil development (moisture, loss on ignition, pH, KCl extractable ions) and groundwater hydrological regime (annual maximum and minimum water levels and range, duration of flooding) were established to define the environmental tolerances of different communities. In multivariate analysis of the vegetation, the dominant gradient was hydrological: dry to wet, followed by a secondary soil development gradient: young calcareous organic-poor soils to acidic/neutral soils with greater organic matter contents. Most measured hydrological and soil variables explained a significant proportion of observed variation in species composition when tested individually, with the exception of soil nitrate and soil calcium concentrations. Maximum water level was the key hydrological variable, and soil moisture and soil pH were the key soil variables. All hydrological and soil parameters together explained 22.5% of the total species variation. There were significant differences in hydrological and soil parameters between community types, with only 40 cm difference in mean annual minimum water levels (averaged over 4 years) separating the wettest and the driest dune slack communities. Therefore, predicted declines in water level exceeding 100 cm by 2080 are likely to have a major impact on the vegetation of these priority conservation habitats.

Establishment of scatter factors for use in shielding calculations and risk assessment for computed tomography facilities

The specification of shielding for CT facilities in the UK and many other countries has been based on isodose scatter curves supplied by the manufacturers combined with the scanner's mAs workload. Shielding calculations for radiography and fluoroscopy are linked to a dose measurement of radiation incident on the patient called the kerma-area product (KAP), and a related quantity, the dose-length product (DLP), is now employed for assessment of CT patient doses. In this study the link between scatter air kerma and DLP has been investigated for CT scanners from different manufacturers. Scatter air kerma values have been measured and scatter factors established that can be used to estimate air kerma levels within CT scanning rooms. Factors recommended to derive the scatter air kerma at 1 m from the isocentre are 0.36 µGy (mGy cm)(-1) for the body and 0.14 µGy (mGy cm)(-1) for head scans. The CT scanner gantries only transmit 10% of the scatter air kerma level and this can also be taken into account when designing protection. The factors can be used to predict scatter air kerma levels within a scanner room that might be used in risk assessments relating to personnel whose presence may be required during CT fluoroscopy procedures.

Synaptonemal complex karyotype of zebrafish

Meiotic cells of zebrafish have been prepared to show synaptonemal complexes (SCs) by light and electron microscopy. Completely paired SCs from both spermatocytes and oocytes were measured to produce an SC karyotype. The SC karyotype resembles the somatic karyotype of zebrafish and has no recognisable sex bivalent. Measurements of total SC length indicate that SCs grow longer and develop centromeres during pachytene. Oocytes consistently have longer SCs than spermatocytes, presumably correlated with the reported higher recombination frequency in females than in males.

Body surface area estimation in children using weight alone: application in paediatric oncology

The majority of chemotherapy regimens and trials specify doses of cytotoxic drugs normalized to body surface area. Estimation of BSA in paediatric patients is particularly problematic, as conventional nomograms require accurate determination of both height and weight. The chemotherapy standards group of the UKCCSG (United Kingdom Children's Cancer Study Group) has evaluated a method for calculation of body surface area (BSA) estimation, based solely on patient weight. In comparison with BSA estimations using 2 commonly used methods, which require both weight and height measurements, deviation in the estimate of BSA was less than 10%. This method may be extended to the dosing of chemotherapeutic agents in infants of body weight less than 10 kg, with appropriate recommendations for dose modification. Until better correlates of drug clearance, such as GFR for carboplatin, are identified BSA is used to standardize doses for most chemotherapeutic agents. The formula presented here provides a more robust and reliable method of calculation of BSA from weight alone. Although this approach has been shown to be equivalent to other currently used methods, care should be taken extending this calculation of BSA to children less than 10 kg, to obese patients and to those with cachexia.

The role of cortical activity in experience-dependent potentiation and depression of sensory responses in rat barrel cortex

The role of cortical activity in experience-dependent cortical plasticity was studied in the rat barrel cortex. Plasticity was induced by depriving every other whisker in a chessboard pattern, which is known to cause depression of responses to deprived whisker stimulation and potentiation of responses to spared whisker stimulation. Postsynaptic activity was blocked by muscimol released from elvax slow-release polymer located under the dura and over the barrel field. Spared whisker responses potentiated 2.5-fold in layer II/III and 2.9-fold in layer IV of the near-neighbor barrel in animals implanted with saline-elvax. In contrast, in whisker-deprived animals implanted with muscimol-elvax, responses were indistinguishable from those in undeprived animals. Similarly, in the spared barrel itself, spared whisker responses potentiated 1.3-fold in layer IV in animals implanted with saline-elvax but not at all in muscimol-treated animals. Whiskers that were deprived and then allowed to regrow showed depressed responses in saline-elvax-treated animals, in which 40% of the cells in layer II/III and 26% in layer IV were unresponsive to their principal whisker. These values fell to 17 and 3% for layers II/III and IV, respectively, in muscimol-treated animals, and the response magnitude distributions were indistinguishable from undeprived cases. Cortical activity block had no acute effect on the ventroposteriomedial nucleus responses and had a transient facilitatory effect after 4 d of muscimol treatment, which returned to baseline as the muscimol treatment wore off. We conclude from these studies that cortical activity is required for potentiation and depression of sensory responses in barrel cortex.

Tongue-base hamartoma in tuberous sclerosis

This paper describes the case of a 41-year-old female with tuberous sclerosis who presented with a large tongue-base hamartoma. The surgical management of the patient was complicated by the presence of a large thyroid goitre. Awake fibre-optic intubation, thyroidectomy then tracheostomy were necessary before the tongue-base hamartoma could be safely resected. To the best of our knowledge, this is the first reported case of a tongue-base hamartoma in a patient with tuberous sclerosis.

Control of influenza A on a bone marrow transplant unit

In January 1998, an outbreak of influenza A occurred on our adult bone marrow transplant unit. Aggressive infection control measures were instituted to halt further nosocomial spread. A new, more rigorous approach was implemented for the 1998/99 influenza season and was extremely effective in preventing nosocomial influenza at our institution.

Sex reversal of the newt Triturus cristatus reared at extreme temperatures

Crested newt larvae were reared at defined temperatures, either from uncleaved eggs or from early feeding larvae, until metamorphosis when sexual differentiation had occurred. Trials at 18-24 degrees C showed a 1:1 sex ratio. A higher temperature trial produced more males than females, including some XX neomales. Lower temperatures resulted in a significant excess of females, including XY neofemales. Sex reversal only occurred in about half the possible cases on average. Extreme temperatures must perturb the normal XX/XY system of sex determination, to reveal either an ancestral ZZ/ZW system or a still more primitive environmental control. It is suggested that neofemales (but not neomales) could occur in nature.

Pre-selection of integration sites imparts repeatable transgene expression

Variable gene expression amongst transgenic lines occurs due to copy number and to random associations of incoming DNA with chromosomal elements at the site of integration. Here we describe a method of identifying sites permissive for transgene expression and their use for efficient introduction of single copy transgenes by homologous recombination. ES clones were selected in HAT medium for expression of a randomly integrated HPRT marker lying 5' to an Oct4/ lacZ transgene. 794 clones were assessed in vitro for appropriate down-regulation of lacZ following differentiation. Two clones were chosen for further analysis which displayed appropriate and inappropriate gene regulation (clones 710 and 91, respectively). Three developmental promoters (thyroglobulin, Hox2.6 and Myf5) were then sequentially introduced into the original insertion sites in each clone (710 and 91) by homologous recombination, to drive expression of lacZ. Transgenic embryos were assessed for their ability to direct lacZ expression to tissues in which the respective promoter sequences are normally active. The site which appropriately down-regulated lacZ in vitro (710) also showed appropriate in vivo regulation of lacZ from the three developmental promoters. Site 91, however, directed an additional pattern of ectopic expression, which was common to all four promoters. Pre-selection of genomic sites for the introduction of transgenes by gene targeting improves the repeatability of transgene expression and provides an efficient means of single copy transgene introduction by homologous recombination.

Inhibin-B as a test of ovarian reserve for infertile women

The objective of the study was to compare a standard clomiphene citrate challenge test with inhibin-B serum concentrations also obtained on cycle days 3 and 10 as a negative predictor of pregnancy in a group of 106 women at risk for compromised ovarian function. Mean duration of follow-up was 8.25 months in 95 patients with 30 pregnancies recorded (plus one biochemical). Inhibin-B concentrations on cycle days 3 and 10 were correlated only with each other and not with serum oestradiol, follicle stimulating hormone (FSH) and/or pregnancy rates. Pregnancy occurred in 34.5% (10/29) of all patients with inhibin-B values >/=45 pg/ml on cycle day 3 and in 31.8% (21/66) of those with values <45 pg/ml. For FSH >11 mIU/ml on either day, pregnancy rate was 13.6% versus 38.4% for FSH of </=9 mIU/ml (P = 0.03). This study reconfirmed the usefulness of a clomiphene citrate challenge test as an indication of ovarian reserve but failed to find clinical value for inhibin-B testing.

Local cortical interactions determine the form of cortical plasticity

Competitive interactions between left and right eye inputs to visual cortex during development are usually explained by the thalamocortical axons competing more or less well for cortical territory during retraction into eye specific domains. Here we review the evidence for competitive and co-operative interactions between cortical columns in barrel cortex which are present several weeks after retraction of thalamocortical axons into barrels. Sensory responses in barrel cortex can be altered by a period of vibrissa deprivation. It was found that responses to previously deprived vibrissae (that had been allowed to regrow) were depressed more if neighboring vibrissae were spared than if all vibrissae were removed simultaneously. Depression of the deprived vibrissa response was greater the closer the cell lay to a spared barrel. It was also found that spared vibrissae responses were potentiated more if several neighboring vibrissae were left intact than if only a single vibrissae was spared. These results suggest a mechanism of cooperative potentiation, perhaps due to intracortical summation of excitation evoked by neighbouring vibrissa stimulation. Thalamic responses to vibrissa stimulation were unaffected by deprivation indicating a cortical origin. One of the consequences of deprivation was that the speed of transmission between barrels was increased for spared and decreased for deprived vibrissa. These results imply that inherent interactions between cortical columns give rise to a property of competition and co-operativity which amplify the effects of sensory deprivation.

Prolactin and growth hormone stimulation of lactation in mice requires thyroid hormones

This experiment tested the hypothesis that thyroid hormones are essential for a milk production response to growth hormone (GH) and prolactin (PRL). Prior to breeding, female transgenic mice expressing the herpes simplex type-I thymidine kinase in the thyroid were treated with ganciclovir to ablate thyroid follicular cells. To provide for normal gestation, thyrocyte-ablated mice were supplied thyroxine (T4) in drinking water (0.2 microgram/ml) until 7 days before parturition. Litter size was adjusted to 9 pups, hormone administration began on Day 2 of lactation, and mice were sacrificed on Day 12. There were 5-6 mice in each of 7 treatments that included nonablated controls, thyrocyte-ablated controls, and thyrocyte-ablated mice treated with T4, GH, PRL, GH + T4, and PRL + T4. Thyroxine was administered in drinking water, and GH and PRL (20 microgram/d) were administered by subcutaneous injection. Compared with thyrocyte-ablated controls, litter weight gain was unaffected when dams were treated with GH, PRL, or T4 alone. However, when dams were treated with GH or PRL in combination with T4, litter weight gain increased 13% compared with thyrocyte-ablated controls and 18% compared with GH or PRL-treated mice. Concentration of T4 in serum of pups averaged 62 ng/ml and did not differ among treatments. Concentration of T4 in serum of dams averaged 76 ng/ml when T4-treated. Thyroxine 5'-deiodinase (5'D), the enzyme that converts T4 to triiodothyronine, was quantitated in liver, kidney, and mammary gland. Quantity of 5'D was lower in liver and kidney of thyrocyte-ablated dams without T4 than in respective tissues of mice treated with T4, and there was no effect of GH or PRL. However, in mammary gland, 5'D was increased by treatment with GH, PRL, or T4. Data show that thyroid hormones are necessary for a galactopoietic response to GH and PRL and demonstrate a unique organ-specific regulation of 5'D by galactopoietic hormones.

The effect of vibrissa deprivation pattern on the form of plasticity induced in rat barrel cortex

Plasticity was induced in the barrel cortex of adolescent rats by depriving every second vibrissa on the contralateral vibrissa pad. This produced a chessboard pattern of barrels in the cortex where each barrel receiving its principal input from a spared vibrissa was surrounded by barrels for which the principal vibrissa had been deprived and conversely, each barrel receiving its principal input from a deprived vibrissa was surrounded by barrels for which the principal vibrissa had been spared. After 7 days' deprivation, responses to the regrown vibrissae were depressed in layers II/III (49% of control levels) and IV (60%). Depression was far greater than that seen with "all vibrissa" deprivation, suggesting that activity in the spared vibrissae accentuated the depression of the deprived vibrissae. Depression was not due to subcortical changes as thalamic Ventral Posterior Medial (VPM) responses to deprived vibrissa were unchanged. The short latency responses in layer IV (5-7 ms) were unaffected by deprivation, but the number of cells responding at intermediate latencies (8-13 ms) was markedly reduced (to 66% of control). Potentiation of the spared vibrissa response was substantial in the near side of the neighbouring barrel (2.2-fold increase in layers II/III, 2.9-fold in layer IV) but had not spread to the far side after 7 days' deprivation. Sparing multiple vibrissae may increase the rate of potentiation since 7 days is insufficient time for potentiation in single vibrissa spared animals. Potentiation was not due to subcortical changes as thalamic VPm responses to the spared vibrissa were normal. However, in the spared barrel the response latency decreased by 1-2 ms. Only the cells responding at short latency exhibited potentiated responses (39% increase) suggesting that some thalamocortical plasticity is still possible at P28-35. These results show that chessboard pattern deprivation is capable of inducing substantial plasticity over a wide area of barrel cortex. All the major forms of plasticity seen with other vibrissa deprivation patterns were present, although no other single deprivation pattern studied so far causes the complete repertoire seen with chessboard deprivation.

Amphibian sex determination and sex reversal

Amphibians employ a genetic mechanism of sex determination, according to all available information on sex chromosomes or breeding tests. Sex reversal allows breeding tests to establish which sex is heterogametic and provides an indication of the mechanism of sex determination. Cases of spontaneous and experimental sex reversal (by temperature, hormones or surgery) are reviewed and illustrated by previously unpublished studies on crested newts. These newts respond conventionally to temperature and hormone treatment but provide anomalous results from breeding tests. It is suggested that both the evolution from temperature dependency to a genetic switch and from ZZ/ZW to XX/XY are superimposed on a generally uniform mechanism of sex determination in all vertebrates.

Impaired experience-dependent plasticity in barrel cortex of mice lacking the alpha and delta isoforms of CREB

The transcription factor cyclic-AMP response element binding protein (CREB) has been implicated in long-term plasticity processes in vertebrate and invertebrate species. In the absence of the alpha/delta CREB isoforms, performance is impaired in long-term memory tasks and the long-term maintenance of long-term potentiation (LTP) is impaired in the hippocampus. However, it is not known whether CREB plays a role in neocortical plasticity. Antibodies to CREB revealed that CREB-immunoreactive nuclei are present in all cortical layers but are more numerous in layers II/III, where they composed at least two-thirds the total population of cells. CREB-immunopositive cells were therefore present and densest in the very cortical layers that exhibit experience-dependent plasticity at this age. In order to assess the role of CREB in neocortical plasticity, we studied the effect of vibrissae deprivation on receptive field plasticity in the barrel cortex of mutant mice lacking the alpha/delta isoforms of CREB. A single vibrissa was spared and the others removed for 18 days. In wild-types this caused potentiation of the spared vibrissa response. However, in adult mutants (>6 months) spared vibrissa responses from homozygotes were potentiated less than in any adolescent animals or in adult wild-type littermates. Surround receptive field responses were abnormally large in homozygotes and failed to increase by the same amount as they did in wild-types. In contrast, the alpha/delta CREB mutation had no discernible effect on plasticity in cortical layers II/III of the younger adolescent age group (1-2 months), suggesting that different plasticity processes may operate at this age. Further tests showed that the beta isoform of CREB was up-regulated in the barrel cortex of the alpha/delta CREB knock-outs, suggesting that this subunit may have compensated partly for the loss of the alpha/delta isoforms. These studies suggests that CREB plays a role in experience-dependent plasticity in the adult neocortex.

The role of uncontrollable trauma in the development of PTSD and alcohol addiction

After a traumatic event, people often report using alcohol to relieve their symptoms of anxiety, irritability, and depression. Alcohol may relieve these symptoms because drinking compensates for deficiencies in endorphin activity following a traumatic experience. Within minutes of exposure to a traumatic event there is an increase in the level of endorphins in the brain. During the time of the trauma, endorphin levels remain elevated and help numb the emotional and physical pain of the trauma. However, after the trauma is over, endorphin levels gradually decrease and this may lead to a period of endorphin withdrawal that can last from hours to days. This period of endorphin withdrawal may produce emotional distress and contribute to other symptoms of posttraumatic stress disorder (PTSD). Because alcohol use increases endorphin activity, drinking following trauma may be used to compensate this endorphin withdrawal and thus avoid the associated emotional distress. This model has important implications for the treatment of PTSD and alcoholism.

Age-specific incidence and prevalence rates of treated epilepsy in an unselected population of 2,052,922 and age-specific fertility rates of women with epilepsy

BACKGROUND

There are no data on prevalence or incidence of treated epilepsy, and no data on fertility of women with epilepsy from an unselected UK population.

METHODS

We used the General Practice Research Database to ascertain the incidence and prevalence of people with treated epilepsy in an unselected population of 2,052,922 people in England and Wales, and also age-specific fertility rates. We defined period prevalence of treated epilepsy as the number of people with epilepsy taking an antiepileptic drug per 100,000 people during 1995. The incidence of treated epilepsy was defined as the number of new cases of treated epilepsy per 100,000 people during the same period. We calculated fertility rates among women with treated epilepsy between 1991 and 1995 and compared these rates with the population rates for England and Wales in 1993.

FINDINGS

The period prevalence of treated epilepsy in 1995 was 5.15 per 1000 people (95% CI 5.05-5.25). The prevalence was lower in children (age 5-9 years 3.16 [2.86-3.48]; 10-14 years 4.05 [3.70-4.42]), and higher in older people (65-69 years 6.01 [5.50-6.57]; 70-74 years 6.53 [5.97-7.14]; 75-79 years 7.39 [6.73-8.11]); 80-84 years 7.54 [6.78-8.39]; 85 years and older 7.73 [6.98-8.66]). The incidence of treated epilepsy was 80.8 per 100,000 people (76.9-84.7). The incidence was lower in children (5-9 years 63.2 [50.5-79.1]; 10-14 years 53.8 [42.4-68.3]) and higher in older people (65-69 years 85.9 [68.5-107.3]; 70-74 years 82.8 [65.0-105.2]; 75-79 years 114.5 [116.9-179.2]; 80-84 years 159 [125.2-202.6]; > or = 85 years 135.4 [100.4-178.7]). Fertility was lower among women with treated epilepsy, with an overall rate of 47.1 livebirths per 1000 women aged 15-44 per year (42.3-52.2), compared with a national rate of 62.6 in the same age-group. The standardised fertility ratios were significantly lower between the ages of 25 and 39 years in women with epilepsy (p<0.001).

INTERPRETATION

Compared with previous studies, we found that the incidence of epilepsy was higher in elderly people and lower in children. The prevalence rates also increase with age. Women aged 25-39 years with treated epilepsy have significantly lower fertility rates than those in the general population. Research is needed to identify any potentially preventable causes for the low fertility rates.

Effects of thyroid hormone deficiency on mice selected for increased and decreased body weight and fatness

A study was undertaken to test whether the elimination of metabolic pathways strongly involved in growth and fatness, comprising thyroid hormones (TH) and growth hormone (GH), is responsible for a substantial part of the genetic change produced by selection. Lines used in this study have been selected for about 50 generations for high (PH) and low (PL) body weight at 10 weeks and for high (F) and low fat content (L) at 14 weeks, producing a 3-fold difference in body weights and a 5-fold difference in fat content. Thyroid ablation was achieved by repeated backcrossing into the four selection lines of a transgene comprising the HSV1-tk gene coupled to the promoter of the thyroglobulin gene. Hemizygous pregnant dams were treated with ganciclovir leading to thyroid-ablated dams and offspring and therefore to a lack of TH and subsequently of GH. In the absence of TH and GH, lines still differ in body weight over the period studied (10 d to about 100 d; e.g. at the end PH = 32.1 g vs PL = 10.2 g) and in fat content (F = 16.2% vs L = 3.8%); the corresponding values for the wild-type controls were PH = 49.9 g vs PL = 17.4 g and F = 27.5% vs L = 4.8%. The effect of the transgene depended on the genetic background for body weights at most ages and for relative gonadal fat pad weights, but less for fat content. The L line showed the lowest growth depression. The lit gene, which causes GH but not TH deficiency, was also transferred by repeated backcrosses into three of these lines (PH, PL, F). The combined deficiency of TH and GH had bigger effects on body weights at earlier ages than did GH deprivation. The data show that changes in the TH- and GH-systems are not the only cause of line differences in growth and fatness resulting from long-term selection, but both are involved to a significant extent. The interactions between the effects of the transgene and of the lit gene and the genetic background were, nevertheless, relatively small and therefore these results support a polygenic model of selection response.

Ethanol, body temperature and thermoregulation

1. The effects of ethanol on body temperature (Tb) and on the regulator of Tb are reviewed. 2. The first section considers how ethanol affects cellular function and how temperature modifies these effects. 3. The next section reviews the effects of ethanol on Tb, covering both disruptive effects and effects on regulatory elements. 4. The final section covers recent work that has made use of genetic techniques to elucidate specific aspects of how ethanol affects temperature regulation.

Lampbrush chromosomes and chiasmata of sex-reversed crested newts

Triturus cristatus carnifex provides a particularly clear example of sexual dimorphism for chiasma frequency and localisation. Oocytes from normal XX females routinely carry one proximal chiasma on each arm of their lampbrush bivalents. Spermatocytes from normal XY males have more numerous and relatively distal chiasmata. Lampbrush chromosomes from the oocytes of sex-reversed XY neofemales are found to resemble those from normal oocytes in having one proximal chiasma on each bivalent arm. A comparison of particular markers on the heteromorphic long arm of chromosome 1 provides evidence to equate the lampbrush 1A to somatic 1A, and confirms previous reports that lampbrush chromosome 1A is slightly longer than 1B. The XY sex bivalent of neofemales does not show any obvious heteromorphy of recognised marker loops.

Effects of thyroid hormone on embryonic oligodendrocyte precursor cell development in vivo and in vitro

The oligodendrocyte precursor cell divides a limited number of times before terminal differentiation. The timing of differentiation depends on both intracellular mechanisms and extracellular signals, including mitogens that stimulate proliferation and signals such as thyroid hormone (TH) and retinoic acid (RA) that help trigger the cells to stop dividing and differentiate. We show here that, both in vivo and in vitro, TH is required for the normal development of rodent optic nerve oligodendrocytes, although in its absence some oligodendrocyte development still occurs, perhaps promoted by signals from axons. We also demonstrate that TH from both mother and pup plays a part in oligodendrocyte development in vivo. Finally, we show that precursors in embryonic nerve cultures differ from those in postnatal cultures in two ways: they respond much better to TH than to RA, and they respond more slowly to TH, suggesting that oligodendrocyte precursor cells mature during their early development.

Risk status at discharge and cause of death for postneonatal infant deaths: a total population study

OBJECTIVES

To obtain population-based, clinical information regarding potentially modifiable factors contributing to death during the postneonatal period (28 to 364 days), we examined all postneonatal infant deaths in four areas of the United States to determine: (1) the cause of death from clinical and autopsy data rather than vital statistics, (2) whether death occurred during initial hospitalization or after discharge, and (3) the portion of postneonatal mortality attributable to infants who left the hospital with identified high-risk medical conditions.

DESIGN AND SETTING

Retrospective medical record review of all postneonatal infant deaths with birth weights greater than 500 g (total N = 386) born to mothers residing in: (1) the city of Boston (1984 and 1985, N = 55), (2) the city of St Louis and contiguous areas (1985 and 1986, N = 123), (3) San Diego County (1985, N = 112), and (4) the state of Maine (1984 and 1985, N = 96). Deaths were identified using linked birth and death vital statistics, and medical record audits of infants' and mothers' charts were performed. Causes of death were obtained from medical record review in conjunction with autopsy if performed (72%, N = 278), medical record alone (17%, N = 67), or vital statistics if no other source was available (11%, N = 41). The medical conditions at the time of discharge for each infant were reviewed and, if judged to confer an increased risk of morbidity or mortality, were classified as high risk.

RESULTS

The causes of death were sudden infant death syndrome (47%, N = 181), congenital conditions (20%, N = 77), prematurity-related conditions (11%, N = 43), infections (9%, N = 34), external causes (including injuries, drownings, ingestions, and burns) (7%, N = 25), and other (6%, N = 23). In 24% of congenital and 25% to 44% of prematurity-related deaths, infection was the acute or associated cause of death. Infants born to black mothers were more likely than those born to white mothers to die during the postneonatal period of all major causes of death (7.3 per 1000 vs 3.0 per 1000). Overall, 18% (N = 68) of deaths occurred to infants who never left the hospital; 79% (N = 305) of the infants were discharged before death; and discharge status was unknown in 3% (N = 13). Eighty-one percent of all infants with prematurity-related postneonatal deaths were never discharged, and of the total infants who were initially discharged, only 1% (N = 4) subsequently died of prematurity-related causes. Of all postneonatal deaths, only 16% (N = 62) left the hospital with identified high-risk medical conditions.

CONCLUSIONS

These findings suggest that the etiology of postneonatal mortality is heterogeneous, with significant complexity in attributing specific causes of death and making designations of "preventability." The vast majority of infants who died of prematurity-related postneonatal causes never left the hospital, and only a small percentage of all infants that left the hospital before death were identified as being at high medical risk. Therefore, strategies for further decreasing postneonatal mortality must link high-risk follow-up programs to more comprehensive strategies that address risk throughout pregnancy and early childhood.

Selective ablation of differentiated cells permits isolation of embryonic stem cell lines from murine embryos with a non-permissive genetic background

Embryonic stem (ES) cells enable the engineering of precise modifications to the mouse genome by gene targeting. Although there are reports of cultured cell contributions to chimaeras in golden hamster, rat and pig, definitive ES cell lines which contribute to the germline have not been demonstrated in any species but mouse. Among mouse strains, genetic background strongly affects the efficiency of ES isolation, and almost all ES lines in use are derived from strain 129 (refs 1,4,5) or, less commonly, C57BL/6 (refs 6-8). The CBA strain is refractory to ES isolation and there are no published reports of CBA-derived ES lines. Hence, CBA mice may provide a convenient model of ES isolation in other species. In ES derivation it is critical that the primary explant be cultured for a sufficient time to allow multiplication of ES cell progenitors, yet without allowing extensive differentiation. Thus, differences in ES derivation between mouse strains may reflect differences in the control of ES progenitor cells by other lineages within the embryo. Here we describe a strategy to continuously remove differentiated cells by drug selection, which generates germline competent ES lines from genotypes that are non-permissive in the absence of selection.

Ganciclovir-induced ablation non-proliferating thyrocytes expressing herpesvirus thymidine kinase occurs by p53-independent apoptosis

In adult mice of the transgenic strain TG66.19, in which expression of herpes simplex type 1 virus thymidine kinase (HSVI-TK) is driven in thyrocytes from the thyroglobulin promoter, the drug Ganciclovir causes the death (ablation) of thyrocytes. Ablation occurred in the absence of thyrocyte proliferation or nuclear DNA synthesis, but was accompanied by transient expression of proliferating cell nuclear antigen and the dying thyrocytes exhibited the ultrastructural features of apoptosis. Control experiments show that the apoptosis is a result of the production of Ganciclovir phosphates in thyrocytes that express HSV1-TK. However, cell death was not dependent upon the presence of a functional copy of the oncosuppressor gene p53. We conclude that the apoptosis is probably not mediated by induction of DNA damage and occurs via a pathway that is independent of p53. The fact that Ganciclovir phosphate can kill cells by a p53-independent apoptotic pathway is encouraging in relation to tumour ablation by methods based on transfection with HSV1-tk genes and administration of Ganciclovir.

Case report: immunoglobulin M-mediated, temperature-dependent neutrophil agglutination as a cause of pseudoneutropenia

The authors report the case of a 77-year-old man in whom intermittent neutropenia developed during a prolonged hospitalization. Laboratory records revealed wide variations in the patient's routine leukocyte counts. Examination of the peripheral smear revealed clumps of 2-3 polymorphonuclear leukocytes throughout the slide and large aggregates (> 50 cells) along the smear edges. Neutrophil clumping also was observed in blood anticoagulated with citrate or heparin. Replacement of patient plasma with saline prevented agglutination. Addition of patient plasma or serum to normal cells induced neutrophil agglutination. Holding the patients blood at 37 degrees C prevented agglutination, which occurred spontaneously and more exuberantly as the temperature was reduced to 22 degrees C. Flow cytometry revealed immunoglobulin M on neutrophil surfaces. Spontaneous agglutination resolved 6 months after resection of the patient's subsequently diagnosed colon cancer. This is the first report of immunoglobulin M-induced neutrophil clumping occurring in the setting of malignancy, and the first reported immunoglobulin M not to require ethylenediaminetetraacetic acid as a cofactor for agglutination.

Complete meiotic pairing of crested newt chromosomes

The longest chromosome (number 1) of Trituturus cristatus carries a heteromorphic segment, a heterozygosity perpetuated by a balanced lethal system. The heteromorphic segment is regarded as achiasmate and has been claimed to be asynaptic. Direct observations of chromosome pairing in spermatocytes and oocytes yield some cases where all homologous chromosomes appear to be completely paired, but the individual bivalents could not be identified as pachytene is not particularly clear in this species. The long arms of bivalent 1 usually remain attached by a terminal chiasma in spermatocytes of T. c. cristatus but the corresponding chiasma is only rarely present in T. c. carnifex spermatocytes. Synaptonemal complexes have been measured in both spermatocytes and oocytes of T. c. cristatus. A karyotype constructed from these measurements matches the main features of somatic and lampbrush chromosome karyotypes, indicating that all chromosomes must be completely paired and proportionately represented as synaptonemal complex. The total length of synaptonemal complex is much the same in spermatocytes and oocytes and is similar to the length in spermatocytes of Xenopus laevis. These two amphibian examples supplement a recent survey of other vertebrate classes to reinforce its conclusion that synaptonemal complex length is not related to genome size in vertebrates.Key words: chromosome pairing, synaptonemal complex, genome size, amphibia.

Different transmission rates of herpesvirus thymidine kinase reporter transgenes from founder male parents and male parents of subsequent generations

Previously we demonstrated that lines of transgenic mice carrying the herpes simplex type 1 virus thymidine kinase (HSV1-tk) reporter gene are male-sterile. Ectopic transcription of the HSV1-tk reporter in the testis was initiated downstream of the normal translation initiation codon and truncated proteins consistent with translational initiation at the second and third ATG codons were synthesized. Here we describe the effects on fertility 1) of converting the second and third ATG codons of the HSV1-tk reporter to CTG codons and 2) of utilizing the HSV type 2 thymidine kinase (HSV2-tk) reporter gene, in which the second ATG codon is located downstream of the ATP-binding pocket of the enzyme. Both reporters were coupled to the bovine thyroglobulin promoter (bTG-tk1 alpha and bTG-tk2 transgenes). The level of ectopic expression of these transgenes in the testis, relative to expression in the thyroid, was one to two orders of magnitude less than that of bTG-tk1. Sixty percent of male founders carrying the bTG-tk1 alpha and bTG-tk2 transgenes were fertile but did not transmit the transgene. In contrast, most males from subsequent generations were fertile and transmitted the transgenes at the expected frequency. This difference between founder males and male descendants is also observed with certain constructs in which the HSV1-tk reporter is coupled to other promoters. We attribute the effect to mosaicism among male founders, leading to competition between transgenic and nontransgenic spermatozoa and/or spermatogenic precursor cells and resulting in a lack of fertilization by transgenic sperm that would successfully fertilize eggs in the absence of competition.

Effects of perinatal thyroid hormone deprivation on the growth and behaviour of newborn mice

Experiments were designed to distinguish between neonatal effects due to maternal thyroxine (T4) deprivation and those due to autonomous (fetus/pup) T4 deprivation, employing mice heterozygous for the bTG-tk transgene TG66,19 which specifically directs high-level expression of herpes virus type I thymidine kinase to the thyrocytes. Heterozygous TG66.19 females were either untreated or Ganciclovir was administered to destroy their thyrocytes and so render them T4-deficient. When mated to normal males these heterozygous females are expected to produce on average 50% normal and 50% heterozygous transgenic conceptuses. Ganciclovir was administered to the dams (both untreated and Ganciclovir-pretreated) during days 14-18 of gestation. At optimum levels of in utero Ganciclovir administration the non-transgenic pups showed no discernible effect while the transgenic pups were rendered athyrocytic and completely T4-deficient. The dams pretreated with Ganciclovir are hypothyroid throughout gestation, while the dams to which Ganciclovir was administered for the first time during gestation are not expected to become hypothyroid until about the time of parturition. In this way four sets of pups were generated for purposes of comparison: hypothyroid (transgenic) and euthyroid (non-transgenic) pups born to euthyroid dams and hypothyroid and euthyroid pups born to hypothyroid (Ganciclovir-pretreated) dams. Normal growth during days 1-10 after birth was dominated by the T4 status of the dam during gestation. Growth during days 11-21 and the correct timing of eye opening and ear elevation were dominated by the autonomous T4 status of the fetus/pup. The timely development of the surface-righting reflex (relative to weight gain) was shown to require both maternal and fetus/pup T4. The development of the cliff-avoidance reflex was independent of the T4 status of both pup and dam and of pup weight. The size of the pups at birth depended primarily on a normal T4 status in the dam but surprisingly T4 deficiency in fetuses/pups partly compensated for maternal T4 deficiency. The results presented here clearly demonstrate the utility of the HSV-tk-transgene-Ganciclovir-administration protocol in studying the interplay of maternal and fetal T4 deprivation in rodents.

Consequences of thyroid hormone deficiency induced by the specific ablation of thyroid follicle cells in adult transgenic mice

The herpes simplex type 1 virus thymidine kinase (HSV1-TK) reporter gene was coupled to a bovine thyroglobulin promoter (TG-tk construct). Within the thyroid glands of transgenic mice expression was confined to thyroid follicle cells. Infusion of Ganciclovir (9-[(1,3-dihydroxy-2-propoxy)methyl]guanine) to 8 to 12 week transgenic females led to the complete loss of thyroid HSV1-TK activity (at 3 to 4 days) and thyroid follicles (between 7 and 14 days). During the first 5 days of treatment a single reciprocal oscillation in circulating thyroxine (T4) and TSH levels occurred. By 14 days the circulating tri-iodothyronine (T3) and T4 levels of all treated animals were below the detection limits of the assays, while TSH levels were elevated ten-fold and continued to increase thereafter. During 14 days of treatment the thyroids regressed, protein content fell by 80-90% and the C cells, normally dispersed within the central region of each gland, came together in aggregates. Pituitary GH levels in females rose and fell back to normal within 14 days and between 14 and 28 days fell to a level comparable with that of GH-deficient lit/lit mice. The levels of hepatic GH receptor mRNA and the predominant 6.6 kb T3 receptor mRNA were unaffected by thyrocyte ablation. Thyrocyte ablation had no effect on the level of prolactin (Prl) receptor mRNA in females, but increased Prl receptor mRNA levels in males and eliminated group 1 major urinary protein (MUP).mRNA in females. T4 replacement reversed the effects of thyrocyte ablation on MUP mRNA in females and on Prl receptor mRNA in males.2+ Despite the many physiological changes induced by thyrocyte ablation, ablated mice have been maintained for up to 1 year without thyroid hormone supplementation. T4-deficient females were normally fertile and carried pups to term. Although transgenic males expressed HSV1-TK ectopically in spermatids and spermatozoa at levels similar to thyrocyte levels, a rate of Ganciclovir infusion which successfully ablated the thyrocytes did not affect the testis. As an alternative to infusion by minipump, thyrocyte ablation could be achieved by 6 twice-daily injections of Ganciclovir, at a level of 112 micrograms Ganciclovir/g body weight per day, and fetuses in utero could be thyrocyte ablated by administering 50 or 15 micrograms/g body weight per day to pregnant females between days 14 and 18 of gestation. These data demonstrate the potential value of transgenic thyrocyte ablation in the study of the effects of thyroid hormone deprivation.

Autoantibodies to myeloperoxidase in idiopathic and drug-induced systemic lupus erythematosus and vasculitis

Circulating antibodies to myeloperoxidase (MPO) have been described in a variety of vasculitic syndromes, drug-induced SLE and drug-induced nephritis. We have examined the autoantibody profile in acute sera from patients with antineutrophil cytoplasmic antibody-positive vasculitis (n = 8), drug-induced nephritis (n = 4), drug-induced lupus (n = 7), SLE (n = 27) and nephritis-associated with SLE (n = 17). Significant binding to purified MPO in ELISA was given by all sera from patients with vasculitis and drug-induced nephritis but ANA sought by indirect immunofluorescence on HEp-2 cells were not detected. Both anti-MPO and ANA were found in sera from patients with drug-induced lupus. Sera from patients with SLE or SLE nephritis did not contain high titres of anti-MPO antibodies but invariably contained ANA. Anti-MPO antibodies of both IgG and IgM classes were present in all sera from patients with drug-induced disease. Although the number of samples tested was small, sera from patients with drug-induced nephritis showed significantly greater median % binding of IgM to MPO compared with drug-induced SLE. Binding to MPO by IgG in these sera was not significantly different. These findings suggest that the mechanism of interaction between hydralazine and the immune system in the two drug-induced autoimmune diseases studied may contribute to their distinct clinical features.

The effect of nonsteroidal agents (NSAIDs) on the pharmacokinetics and pharmacodynamics of metolazone

NSAIDs attenuate the natriuretic response to loop diuretics. Their effect on the action of distal tubular diuretics is poorly explored. Accordingly, the pharmacokinetics and pharmacodynamics of metolazone [M], a distal tubular diuretic, with and without indomethacin [M+I] or sulindac [M+S] were examined in six healthy volunteers. Urine samples were obtained over 36 hours post-metolazone dosing for the determination of sodium, potassium and metolazone concentration. Though cumulative M excretion 750 +/- 247 [mucg/36 h] [M]; 749 +/- 239 [M+I]; 848 +/- 443 [M+S] was comparable between treatment groups, total sodium [Na+] excretion was significantly depressed in the presence of S or I, 685 +/- 114 [mEq/36 h] [M]; 454 +/- 90 [M+I] (p < or = 0.05); 553 +/- 123 [M+S] (p < or = 0.05). Peak Na+ excretion [muEq/min] was significantly decreased by I only and time to peak Na+ excretion did not differ amongst treatment groups. Total potassium [K+] excretion 160 +/- 39 [mEq/36 h] [M]; 111 +/- 53 [M+I] (p < or = 0.05); 135 +/- 31 [M+S] significantly decreased with I. This phenomenon was most evident between 12 and 36 hours. The administration of I or S with M significantly blunted sodium excretion on a purely pharmacodynamic basis while the decline in urinary potassium excretion upon addition of I to M related probably to an attenuation of braking phenomenon induced kaliuresis. These findings likely reflect NSAID-induced sodium reabsorption at loci prior to the site of action of metolazone.

Sexual dimorphism and growth hormone regulation of a hybrid gene in transgenic mice

The sexually dimorphic expression of the urinary protein genes of mice (Mup genes) in the liver is mediated by the different male and female temporal patterns of circulating GH. Normal females were induced to male levels when GH was administered by injection to mimic the male GH pattern, showing that expression at the male level does not require a male sex steroid status in addition to intermittent GH. Two Mup-alpha 2u-globulin hybrid transgenes with different Mup gene promoters showed sexually dimorphic expression, and their expression in females increased to male levels upon testosterone treatment. GH-deficient (lit/lit) mice did not express these transgenes, and GH-deficient females did not respond to testosterone treatment, showing that GH was required for induction. Both normal and GH-deficient females were induced to male levels when GH was administered by injection. This is the first report of a transgene responsive to GH. A transgene consisting of a Mup promoter fused to a Herpes simplex virus thymidine kinase reporter sequence also showed sexual dimorphism, although to a lesser degree. It was expressed at the same level in normal females and GH-deficient mice of both sexes and was induced when GH-deficient mice were treated with GH. We propose that this transgene has a basal constitutive expression, possibly due to the absence of any rodent DNA downstream of the promoter. Since expression of the transgene was significantly induced by GH, the GH response is due at least in part to sequences in the promoter region.

Specific ablation of thyroid follicle cells in adult transgenic mice

The coding region of the herpes simplex type 1 virus thymidine kinase gene was coupled to the promoter of the bovine thyroglobulin gene and introduced into the genome of mice. The viral thymidine kinase (HSV1-TK) was expressed mainly in the thyroid glands and testis. Upon treatment of transgenic females with the antiherpetic agent Ganciclovir the thyroid regressed, while the parathyroid gland was unaffected. The number of thyroid follicle cells was greatly reduced after 3 days, and they were completely absent after 7 days of treatment. After 14 days, the levels of circulating T4 and T3 were below the limits of detection, total soluble protein recovered from the thyroid and parathyroid glands together was 10% of the control value, and the level of thyroid HSV1-TK was more than 100-fold lower than that in transgenic controls. Levels of circulating PTH and calcitonin remained normal. At the time of treatment the mice were adults. Thus, the thyroid follicle cells were selectively ablated after normal development with a functional thyroid gland. When treatment with Ganciclovir was terminated after 14 days, no circulating T4 or T3 or other indications of thyroid regeneration were detected for a subsequent period of 90 days. During this time the mice gained weight more slowly than controls, at a rate consistent with the suppression of GH synthesis by thyroid deficiency. The production of mouse major urinary protein (MUP) ceased in the treated mice and was completely restored by the administration of T4. MUP production was not restored by GH, demonstrating that the expression of the Mup genes requires T4 in addition to GH.

The herpes simplex virus type 1 thymidine kinase is expressed in the testes of transgenic mice under the control of a cryptic promoter

We reported previously that the herpes simplex virus type 1 (HSV-1) thymidine kinase reporter gene (tk) was expressed in the testes of transgenic mice when coupled to the promoter of a liver-specific mouse major urinary protein (MUP) gene. Here we show that HSV-1 tk is also expressed in the testis when coupled to a MUP pseudogene promoter, to a truncated MUP promoter that is not active in the liver, and to the promoter of the bovine thyroglobulin gene. Furthermore, HSV-1 tk itself was expressed in the testis, although its normal expression had been disabled by removing an upstream regulator of transcription. In every case, the same multiple transcripts were observed, with their 5' ends located downstream of the normal HSV-1 tk translation initiation codon. We conclude that the transcription of HSV-1 tk in the testis is directed by a cryptic TATA box-independent promoter located in the coding region of the gene. The longest HSV-1 thymidine kinase (TK) polypeptides synthesized in the testis were shorter than full-length TK and probably result from translational initiation at Met46 and Met60, the second and third ATG codons of the tk reading frame. Male mice of most transgenic lines were sterile, and the severity of the lesion in spermatogenesis was directly related to the level of TK expression. In the most highly expressing lines, sperm counts were low and morphologically defective sperm were common. In other sterile lines, TK was expressed at a lower level and sperm counts were normal but sperm motility was greatly reduced. Lines with the lowest levels of HSV-1 TK expression were fertile. HSV-1 TK was expressed in germ line cells, mainly in the haploid spermatids. However, low-level HSV-1 TK activity was found in the testis before the first germ cells entered meiosis, showing that if expression is confined to the germ cells, it also occurs in spermatogonia.

Islands of acetylated histone H4 in polytene chromosomes and their relationship to chromatin packaging and transcriptional activity

The four histones of the nucleosome core particle are all subject to enzyme-catalysed, post-translational acetylation at defined lysine residues in their amino-terminal domains. Much circumstantial evidence suggests a role for this process in modifying chromatin structure and function, but detailed mechanisms have not been defined. To facilitate studies on the functional significance of histone acetylation, we have prepared antibodies specific for the acetylated isoforms of histone H4. Because of the extreme evolutionary conservation of H4, these antisera can be applied to a wide variety of organisms and experimental systems. In the present study we have used polytene chromosomes from the salivary glands of larvae of the midge Chironomus to examine the distribution of acetylated H4 in interphase chromatin. By indirect immunofluorescence, antisera to acetylated H4 labeled the four Chironomus chromosomes with reproducible patterns of sharply defined, fluorescent bands. An antiserum to non-acetylated H4 gave a completely different, more-diffuse labelling pattern. Thus, there are defined regions, or islands, in the interphase genome that are enriched in acetylated H4. Double-labelling experiments with two antisera specific for H4 molecules acetylated at different sites, showed that each antiserum gave the same banding pattern. Immunolabelling patterns were not dependent on the pattern of phase-dense bands characteristic of these chromosomes; strongly labelled regions could correspond to phase-dense bands (i.e. condensed chromatin), to interbands or, frequently, to band-interband junctions. Immunogold electron microscopy confirmed the immunofluorescence results and showed further that regions of relatively high labelling could be either transcriptionally active or quiescent, as judged by the presence or absence of ribonucleoprotein particles. Two rapidly transcribed genes on chromosome 4 of Chironomus form characteristic ‘puffs’, the Balbiani rings BRb and BRc. The antiserum to non-acetylated H4 gave diffuse labelling throughout these puffs, demonstrating the continued presence of this histone in these transcriptionally active regions. Antisera to acetylated H4 strongly labelled the boundaries of BRb and BRc, and revealed clearly defined islands of increased H4 acetylation just within the expanded chromatin of the puffs. Labelling within the central region of each puff was much less intense. A similar pattern was observed in puffs on other chromosomes. Thus, increased H4 acetylation is not found throughout actively transcribed chromatin but occurs only at defined sites, possibly in the non-transcribed flanking regions. H4 acetylation is clearly not required for the passage of RNA polymerase through the nucleosome and we speculate that its role may be to facilitate the binding to DNA of polymerases and other proteins prior to the onset of transcription and possibly replication.

Abortive development in the crested newt Triturus cristatus

Crested newts exhibit a balanced lethal system which causes development to abort in 50% of tailbud embryos. The main features of arrested embryos are described, shown to be constant in a range of culture conditions and found to be unchanged by parabiosis or extirpation of the central nervous system or heart. Two categories of abortive embryos can be distinguished in some spawnings. A corresponding segregation of an easily identified marker chromosome confirms previous reports that chromosome 1 carries the recessive lethal factors. The marker chromosome is tentatively associated with the blistered form of abortive embryo. Two possible modes of origin for the balanced lethal system are discussed, either from ancestral autosomes or from sex chromosomes. The latter is favoured because it involves fewer assumptions. The subsequent evolution of the system should inevitably lead to progressively earlier embryonic mortality by an accumulation of multiple recessive lethal factors on each chromosome variant.