The ``hitchhiking Effect'''' Revisited

The number of selectively neutral polymorphic sites in a random sample of genes can be affected by ancestral selectively favored substitutions at linked loci. The degree to which this happens depends on when in the history of the sample the selected substitutions happen, the strength of selection and the amount of crossing over between the sampled locus and the loci at which the selected substitutions occur. This phenomenon is commonly called hitchhiking. Using the coalescent process for a random sample of genes from a selectively neutral locus that is linked to a locus at which selection is taking place, a stochastic, finite population model is developed that describes the steady state effect of hitchhiking on the distribution of the number of selectively neutral polymorphic sites in a random sample. A prediction of the model is that, in regions of low crossing over, strongly selected substitutions in the history of the sample can substantially reduce the number of polymorphic sites in a random sample of genes from that expected under a neutral model.     

Brisk walking improves endurance fitness without changing body fatness in previously sedentary women.

The purpose of this study was to examine the influence of brisk walking on endurance fitness and the amount and distribution of body fat in previously sedentary women. Twenty eight women [mean age (SEM): 44.9 (1.5) years] followed the walking programme for 1 year, whilst 16 acted as controls [age 44.4 (2.3) years]. Changes in endurance fitness were evaluated by measuring the oxygen uptake (VO2) at a reference blood lactate concentration of 2 mmol.l-1. Two 1.61-km field tests of walking were completed, one at maximal speed and one at a "brisk" speed, as well as a 1.61-km walk on a motorised treadmill. The amount and distribution of body fat was determined by hydrostatic weighing and anthropometry and energy intake was evaluated using the 7-day weighed food intake method. Walkers completed an average of 157 min.week-1 of brisk walking over the year. The following were increased in walkers, relative to controls: brisk walking speed [walkers 1.73 (0.05) m.s-1 vs 1.88 (0.07) m.s-1; controls 1.69 (0.05) m.s-1 vs 1.70 (0.05) m.s-1 at baseline and 12 months respectively, P < 0.01], maximal walking speed and VO2 at 2 mmol.l-1. In addition, brisk walking reduced heart rate and blood lactate concentration during stepping as well as during standard, submaximal treadmill walking. It did not modify either the amount or the distribution of body fat, despite an unchanged energy intake.     

Constitutive protein secretion by guinea-pig seminal vesicle epithelial cells.

1. Secretion of pulse-labelled protein by the isolated epithelium of guinea-pig seminal vesicle epithelium was rapid, unaffected by cholinergic and adrenergic drugs, cyclic nucleotides or changes in the sodium, potassium and calcium concentrations of the "chase" medium. 2. Low temperature, NH4Cl, hyper- and hypo-osmolarity and membrane-stabilizing agents inhibited secretion which was also dependent on aerobic metabolism. 3. Monensin reduced secretion of the six labelled, relatively low molecular weight proteins recovered from the medium in a concentration-dependent, apparently non-specific manner.     

LCR/MEL: a versatile system for high-level expression of heterologous proteins in erythroid cells.

We have used the human globin locus control region (LCR) to assemble an expression system capable of high-level, integration position-independent expression of heterologous genes and cDNAs in murine erythroleukaemia (MEL) cells. The cDNAs are inserted between the human beta-globin promoter and the second intron of the human beta-globin gene, and this expression cassette is then placed downstream of the LCR and transfected into MEL cells. The cDNAs are expressed at levels similar to those of the murine beta-globin in the induced MEL cells. Heterologous genomic sequences can also be expressed at similar levels when linked to to the LCR and beta-globin promoter. In addition we demonstrate that, after induction of differentiation, MEL cells are capable of secreting heterologous proteins over a prolonged time period, making this system suitable for use in continuous production systems such as hollow fibre bioreactors. The utility of the LCR/MEL cell system is demonstrated by the expression of growth hormone at high levels (greater than 100 mg/l) 7 days after induction. Since the expression levels seen do not depend upon gene amplification and are independent of the integration position of the expression cassette, it is possible to obtain clones with stable high-level expression within 3-4 weeks after transfection.     

Yeast mitochondria (Saccharomyces cerevisiae) contain Ca(2+)-independent phospholipase A1 and A2 activities: effect of respiratory state

We demonstrate that both phospholipase A1 and phospholipase A2 are associated with isolated yeast mitochondria (Saccharomyces cerevisiae). Activity assays indicate that, unlike most other mitochondrial phospholipases A, the yeast enzymes are Ca(2+)-independent with acidic (pH 4-5) as well as alkaline (pH 8-9) pH optima. Data obtained with mitochondria isolated from either fermenting or respiring cells, and initial observations with a petite strain, strongly suggest that a phospholipase A2 with an acidic pH optimum functions in the in vivo adaptation and maintenance of mitochondrial membranes required for respiration.     

Risk of second primary cancers after Hodgkin's disease by type of treatment: analysis of 2846 patients in the British National Lymphoma Investigation.

OBJECTIVE--To analyse the risk of second primary cancers during long term follow up of patients with Hodgkin''s disease. DESIGN--Cohort study. SETTING--The British National Lymphoma Investigation (a collaborative group of over 60 participating centres in Britain treating lymphomas). PATIENTS--2846 patients first treated for Hodgkin''s disease during 1970-87, for whom follow up was complete in 99.8%. MAIN OUTCOME MEASURES--Second primary cancers; uniform pathology reviews confirmed the diagnosis of Hodgkin''s disease and of second primary non-Hodgkin''s lymphomas. RESULTS--113 second primary cancers occurred. Relative risk of cancer other than Hodgkin''s disease was 2.7 (95% confidence interval 2.3 to 3.3) compared with the general population, with significant risk of leukaemia (16.0(9.1 to 26.0)); non-Hodgkin''s lymphoma (16.8(9.8 to 26.9)); and cancers of the colon (3.2 (1.4 to 6.2)), lung (3.8 (2.6 to 5.4)), bone (15.1 (1.8 to 54.7)), and thyroid (9.4 (1.1 to 33.9)). Absolute excess risk associated with treatment was greater for solid tumours than for leukaemia and lymphomas. Relative risk of leukaemia increased soon after treatment, reaching a peak after five to nine years. It was increased substantially after chemotherapy (27.9 (12.7 to 52.9)), combined treatment with radiotherapy and chemotherapy (21.5 (7.9 to 46.8)), and relative to number of courses of chemotherapy but was not significantly increased after radiotherapy (2.5 (0.1 to 14.1)). Relative risk of non-Hodgkin''s lymphoma increased in the first five years after treatment and remained high but showed no clear relation with type or extent of treatment. Relative risk of solid tumours was less raised initially but increased throughout follow up and for lung cancer 10 years or more after entry was 8.3 (4.0 to 15.3). The risk of solid tumours increased after treatments including radiotherapy and after chemotherapy alone. The risk after chemotherapy increased significantly with time since first treatment. CONCLUSION--The risk of solid cancer, not of leukaemia, is the major long term hazard of treatment for Hodgkin''s disease, and this seemed to apply after chemotherapy as well as after radiotherapy. These risks of second cancers are important in choice of treatment and in follow up of patients, but they are small compared with the great improvements in survival which have been brought about by modern therapeutic methods for Hodgkin''s disease.     

Audit of compliance with antenatal protocols.

OBJECTIVE--To assess the implementation of action protocols dictated by antenatal risk factors noted at the initial (booking) antenatal visit. DESIGN--Retrospective study of 2000 women delivered between 1 March 1990 and 29 March 1991. SETTING--Maternity department of a district general hospital supporting a multiethnic population in inner London. MAIN OUTCOME MEASURES--Comparison of clinical actions performed against those dictated by the department''s protocols. Analysis according to clinical importance, gestation at booking, maternal age, parity, birth order, ethnic origin, and certainty of gestational age. RESULTS--Interobserver agreement between the two auditors was good (kappa statistic for risk factors detected, 0.78; for actions generated, 0.80). Of the 15,658 actions dictated by department protocols, 3673 (23.5%) were actually performed by the clinicians. The 63 combinations of risk factors and actions believed by consultants to be of particular clinical importance had an action rate of 28.3% compared with 18.6% for those considered less important (p < 0.001). Mothers who first visited the hospital antenatal clinic at or before 24 weeks'' gestation had 25.2% of relevant protocols fulfilled (p < 0.001). Compliance was significantly improved in women aged 36 or over (32.4%), black women (24.9%), and cases of uncertain gestation (24.5%). Parity and birth order were not associated with an altered action rate. Ethnic origin deemed as "other" (than white, black, Asian, or oriental) or "unknown" was associated with poor compliance (19.3%). CONCLUSIONS--Compliance to a set of agreed protocols was poor even though a computer system was available and a protocol manual had been distributed. Protocols were more likely to be implemented in women who booked early and in some groups of women deemed at high risk including older mothers, black women, and those denoted as having uncertain gestational age.