Analysis of optical density and contrast in mammograms

The objective of this project is the development of tools for the UK NHSBSP to assess image quality quantitatively in clinical films, for the purposes of optimizing imaging procedures and audit. As an initial step, 120 mammograms of 46 women on a single day of screening were digitized and analysed to produce indices of optical density (OD) and contrast. Analysis was performed on three regions of interest (ROI): pectoral muscle, main breast and skin edge. Two radiologists independently graded the quality of information in the different parts of each mammogram, and categorized breast type as either "dense", "mixed density" or "fatty". Measurements of contrast and OD generally correlated well with the opinions of the radiologists. For the oblique mammograms, the mean OD in the main breast ranged between films from 1.25 to 2.24 with a mean of 1.69 +/- 0.02. In the craniocaudal mammograms, the mean OD in the main breast ROI ranged from 1.14 to 1.94 with a mean of 1.61 +/- 0.05. The OD for a quality control film of a 40 mm block of PMMA exposed on the same day with this system was 1.53. A contrast index (CI) was calculated for each mammogram as the difference between the points of maximum and minimum OD in the main breast. Mean CI was 1.02 +/- 0.09 for fatty breasts, 1.50 +/- 0.10 for mixed density breasts and 2.05 +/- 0.23 for dense breasts. A review of the radiologist assessments indicated that the main breast was satisfactorily displayed when glandular and fatty tissues were displayed within the OD range 0.8-2.9. An analysis of the dynamic range requirements showed that 17% of films had a dynamic range that lay above that calculated using the suggested OD limits.

Reduced glycogen phosphorylase activity in denervated hindlimb muscles of rat is related to muscle atrophy and fibre type

Changes in the activity of muscle glycogen synthase or phosphorylase (GP) may be responsible for the deregulation of glycogen synthesis and storage which occurs in diabetes mellitus. To clarify the relationship between muscle atrophy, fibre type, insulin-stimulated glucose uptake and GP activity during insulin resistance, we used sciatic nerve severance to induce insulin resistance in rat hindlimb muscles and compared the above parameters in muscles with a range of fibre types. Changes were analysed by comparison with the contralateral hindlimb, which bears more weight due to denervation of the opposing limb, as well as the sham-operated and contralateral limb of a separate rat. Denervation caused a decrease in insulin-stimulated glucose uptake by 1 day after denervation and a decline of GP activity after 7 days in all muscles investigated. GP activity decreased by 73% in soleus, 36% in red gastrocnemius, 35% in tibialis and 13% in white gastrocnemius, which was related to the degree of muscle atrophy and inversely related to the overall GP activity in non-denervated muscles. GP activity in muscles of the contralateral limb from the denervated rat did not differ from either hindlimb of the sham-operated rat. We conclude that the fibre-type related reduction in insulin-stimulated glucose uptake of denervated muscle determines the change in its metabolism and it is this metabolic change which determines the mechanism, rate and degree of muscle atrophy, which is directly related to the decline in GP activity.

A comparison of cancer detection rates achieved by breast cancer screening programmes by number of readers, for one and two view mammography: results from the UK National Health Service breast screening programme

OBJECTIVE

To determine the increased cancer detection rate, if any, of programmes in the UK National Health Service breast screening programme (NHSBSP) using more than single reading of mammograms.

DESIGN

Information on the detection of cancers by individual screening programmes from annual (KC62) returns, supplemented by questionnaire information about the number of readers.

SETTING

The 87 NHSBSP programmes from England and Wales for the screening year 1 April 1996 to 31 March 1997. The study includes all programmes for prevalent screens where two views are mandatory, but excludes the four programmes using two view mammography for incident screening.

MAIN OUTCOME MEASURES

Cancer detection, invasive cancer detection, and small (< 15 mm) invasive cancer detection by mammographic reading protocol using single reading as the reference level.

RESULTS

Programmes collectively using single reading detected the lowest rate of cancers at both prevalent (first) and incident (subsequent) screening. The highest rate of age standardised cancer detection was achieved by programmes using double reading with arbitration. At prevalent screens, where all programmes used two views, those programmes using double reading with arbitration detected 32% (95% confidence interval (CI) 3% to 69%) more small (< 15 mm) invasive cancers than programmes using single reading. At incident screens, where all programmes analysed used one view this increased to 73% (95% CI 40% to 113%). Recall rates showed no obvious difference between single reading and the double reading protocols, being around 7% for prevalent screens and 3.5% for incident screens.

DISCUSSION

The results suggest that the increase in cancer detection resulting from increasing the number of readers depends on the number of views, and is higher for one view than two views. Single reading of one view results in a low detection rate of small invasive cancers for most individual programmes. It is, however, recognised that a small number of individual readers may achieve high detection rates with such a protocol. All groups of programmes using different reader/view protocols are on average close to or above target cancer detection rates, except those using single reading of one view (mediolateral oblique) at incident screens.

Cloning and characterisation of the gene encoding mole rat (Spalax ehrenbergi) growth hormone

In mammals the structure of pituitary GH is generally strongly conserved, reflecting a slow basal rate of molecular evolution. However, on a few occasions the rate has increased - markedly during the evolution of primates and artiodactyls, and to a small extent during the evolution of rodents and rabbit - giving rise to marked differences between GH sequences of these species. In order to extend knowledge of rodent GHs we have cloned and characterised part of the GH gene of the Eurasian mole rat (Spalax ehrenbergi) using genomic DNA and a PCR technique. The sequence of all of the coding region and 5' untranslated region (UTR), most of the 3' UTR and part of the promoter region is described. The overall organisation of the mole rat GH gene is similar to that of GH genes from other mammals. The proximal Pit-1 sequence in the gene promoter differs somewhat from that of rat or mouse. The deduced sequence for the mature GH from mole rat differs from that of pig GH (thought to be identical to the ancestral placental mammal GH sequence) at 7 residues and from rat, mouse and hamster GHs at 9 to 12 residues. Only one or two of these substitutions involve residues close to the receptor-binding sites of the hormone.

Mentorship in nursing: a literature review

The recent increase in published work relating to the supervision of nurses and in particular mentorship suggests that nurses value the opportunities that such schemes present for developing practice. Much of the literature surrounding mentorship concerns the supervision of students in practice settings but more recently, especially following the changes to post-registration education, attention has shifted to the supervision of qualified nurses. Although the principles of supervision for students and qualified nurses are the same, differences do occur in supervisory practices. This review examines the literature associated with the supervision of student nurses and focuses on the nature and practice of mentorship in practice settings. The literature reveals that confusion exists regarding both the concept of mentorship and the role of the mentor. Many authors propose models or frameworks for mentoring activities. These tend to outline the stages of the mentoring process and the relationship between mentor and mentee. No one model is seen as more appropriate than another and choice usually depends upon the mentor's familiarity with a particular framework. It is also evident that there is inconsistency in the length and level of preparatory courses for mentors. As yet there is in the United Kingdom no national minimum requirement or common preparation route and in practice mentors are prepared by way of the appropriate National Board Teaching and Assessing module and/or short local 2-day course.

Improving uptake in non-attenders of breast screening: selective use of second appointment

OBJECTIVE

To find the most cost and time effective way of increasing uptake by re-invitation of non-attenders after an initial invitation.

SETTING

Women from the Warwickshire, Solihull, and Coventry breast screening programme who failed to attend their initial invitation.

METHOD

Between October 1996 and February 1997, 2229 women who had failed to attend and had not declined their first invitation to screening were split into two groups according to their Sx number (a number allocated to all women when they are called for screening). Women with an odd number received a "open" invitation asking them to telephone the screening unit for another appointment and women with an even number were given a second "fixed" appointment time. The response of both groups of women was monitored.

RESULTS

There was a significant difference (p < 0.001) in response to a second invitation between the open invitation and fixed appointment letter (12.3% v 22.8%). The greatest disparities were between those who had attended screening in both preceding rounds and those who had failed to attend either round. Socioeconomic status measured by Townsend scores did not seem to affect the response to second appointments.

CONCLUSION

Second appointments are an important way of increasing screening uptake and thus reducing mortality, which should not be dismissed. The type of invitation is important, with fixed appointments being more effective, and the best predictor of attendance being attendance in the previous screening rounds. This information can be used to allocate resources efficiently to achieve an increased uptake.

RECOMMENDATIONS

All women should receive a second invitation, ideally as a timed appointment. However, if this appointment strategy prevents an individual screening programme maintaining a three year cycle, we have identified a group of women for whom a simple reminder letter would maintain increased uptake while allowing savings in appointment scheduling.

Slippage in the NHS breast screening programme: an assessment of whether a three year screening round is being achieved

BACKGROUND

The NHS breast screening programme (NHSBSP) was established in 1987 to screen women aged 50-64 every three years to achieve a significant reduction in breast cancer mortality. Ensuring that women are re-invited every three years (that is, a three year screening round is in operation) is becoming increasingly difficult as pressure on the service rises. Coverage measures the proportion of eligible women receiving a screen in the previous three years and is currently used as an NHS performance indicator, while uptake measures the proportion of invited women who attend for screening. Data for 1996/1997 for the West Midlands NHSBSP show that, although uptake among 50-64 year olds was in excess of the 70% target at 78%, coverage was 10% below this at 68%. The discrepancy between coverage and uptake is likely to in part reflect "round slippage" in which women are re-invited at three years or more from their previous screen. To investigate the extent to which slippage is occurring in the region a technique for assessing round length independently of coverage was developed.

METHODS

Records for women receiving routine recall (incident) screens between 1994 and 1997 in the West Midlands NHSBSP were examined and the time between the most recent screen and the previous screen measured in months.

FINDINGS

Of 73,785 women screened in 1996/1997, 46.3% had a round length of under three years, although 74.9% had been re-screened within 38 months of the previous screen. Overall the regional programme was estimated to have a round slippage of approximately two months.

CONCLUSIONS

The West Midlands NHSBSP operates to high standards in terms of uptake and cancer detection, but round slippage must be reduced. The lack of quantitative data with which to assess round length has hindered assessment in the past. The simple technique developed in this study will allow assessment of round length to be used routinely as the key quality assurance measure for the programme.

Cloning and characterisation of the gene encoding red deer (Cervus elaphus) growth hormone: implications for the molecular evolution of growth hormone in artiodactyls

In mammals the structure of pituitary GH is generally strongly conserved, indicating a slow basal rate of molecular evolution. However, on two occasions, during the evolution of primates and of artiodactyls, the rate of evolution has increased dramatically (25- to 50-fold) so that the sequences of human and ruminant GHs differ markedly from those of other mammalian GHs. In order to define further the burst of GH evolution that occurred in artiodactyls we have cloned and characterised the GH gene of red deer (Cervus elaphus) using genomic DNA and a polymerase chain reaction technique. The deduced sequence for the mature GH from red deer is identical to that of bovine GH, indicating that the burst of rapid evolution of GH that occurred in Artiodactyla must have been completed before the divergence of Cervidae and Bovidae and suggesting that the rate of evolution during this burst must have been greater than previously estimated. In other aspects (signal sequence, 5' and 3' sequences, introns and synonymous substitutions in the coding sequence) the red deer GH gene differs considerably from the GH genes of other ruminants. Differences between the signal peptide sequences of red deer and bovid GHs probably explain why N-terminal heterogeneity is seen in bovine, ovine and caprine GHs but not GH from red deer, pig or most other mammals.

Interval breast cancers in the NHS Breast Screening Programme: does the current definition exclude too many?

OBJECTIVES

To examine the impact of the definition of interval breast cancers on interval cancer rates arising from the prevalent (first) screening round.

DESIGN

Interval breast cancers arising from the prevalent (first) screening round at the Warwickshire, Solihull and Coventry Breast Screening Unit (17 April 1989 to 31 March 1992) were identified by comparison of data held at the unit with records at the West Midlands Cancer Intelligence Unit. Exclusion criteria used in National statistics were applied to this sample to quantify their impact on achieved interval cancer rates. The round lengths experienced by individual women at the unit were determined from the prevalent and incident invitation dates for 155 women with incident (re-screen) breast cancers detected in the second round.

SETTING

Warwickshire, Solihull and Coventry Breast Screening Unit.

SUBJECTS

59,017 women screened between 17 April 1989 and 31 March 1992 with a negative screening result and 155 women with incident screen detected cancers.

RESULTS

A total of 278 interval cancers were identified, giving an overall rate from the prevalent screening round of 47.1/10,000 women screened. Of these, 213 met the criteria used in the definition of interval cancers for National statistics and were termed "core" interval cancers. The overall "core" interval rate was 36.1/ 10,000 women screened, similar to interval cancer rates found in the north west of United Kingdom. Thus applying commonly used exclusion criteria produced a 23.4% reduction in the apparent interval cancer rate, with the largest decrease resulting from the exclusion of cancers arising at 36 months or more from the last screen.

CONCLUSIONS

The exclusion criteria used in the definition of interval cancers have a significant impact on observed interval cancer rates. Of particular concern is the exclusion in the current National definitions of cancers arising at 36 months or more from the last screen, which may mask a problem with significant implications for the success of the NHSBSP.

Influence of number of views and mammographic film density on the detection of invasive cancers: results from the NHS Breast Screening Programme

The National Health Service Breast Screening Programme (NHSBSP) has recommended the adoption of two view mammography at the prevalent screen, and the use of a target film density in the range 1.4-1.8. The aim of this study was to review the impact of number of views and optical density on the detection of invasive cancers. The last four annual returns for screening centres in the NHSBSP have been analysed retrospectively for 2827342 women aged 50-64 years attending their first (prevalent) screening examination. The detection of invasive cancers was assessed in relation to the number of views and film density using the age adjusted, Standardized Detection Ratio measure of screening performance. Typical film densities were reported for each screening year by local physicists, and the average value for all mammography sets at each programme calculated, and found to vary from 0.85 to 1.85. The mean film density across the NHSBSP rose progressively from 1.30 (SD = 0.21) in 1991/2 to 1.57 (SD = 0.12) in 1994/5. Programmes using single view mammography (MLO) and an optical density less than 1.4 detected 76% (95% CI 74-79%) of the expected invasive cancers. Programmes using two view mammography (MLO and CC) and an optical density equal to or greater than 1.4 detected 95% (95% CI 92-98%) of the expected invasive cancers. In 1994/95 when more programmes used the recommended screening modes, the NHSBSP detected 96% (95% CI 92-101%) of the expected invasive cancers at prevalent screening. The detection of invasive cancers was highest where programmes used two views with a film density in the range 1.4-1.8. The results provide evidence of the benefit of the recommended protocol for prevalent screening and indicate that from 1995/96 when all programmes will be using the recommended protocol, it is likely that the detection rates and interval cancer rates from prevalent screens in the NHSBSP will be close to the figures in the Swedish-Two County Trial.

In vitro selection of a viomycin-binding RNA pseudoknot

BACKGROUND

The peptide antibiotic viomycin inhibits ribosomal protein synthesis, group I intron self-splicing and self-cleavage of the human hepatitis delta virus ribozyme. To understand the molecular basis of RNA binding and recognition by viomycin, we isolated a variety of novel viomycin-binding RNA molecules using in vitro selection.

RESULTS

More than 90% of the selected RNA molecules shared one continuous highly conserved region of 14 nucleotides. Mutational analyses, structural probing, together with footprinting experiments by chemical modification, and Pb2+-induced cleavage showed that this conserved sequence harbours the antibiotic-binding site and forms a stem-loop structure. Moreover, the loop is engaged in a long-range interaction forming a pseudoknot.

CONCLUSIONS

A comparison between the novel viomycin-binding motif and the natural RNA target sites for viomycin showed that all these segments form a pseudoknot at the antibiotic-binding site. We therefore conclude that this peptide antibiotic has a strong selectivity for particular RNA pseudoknots.

Function switching as a basis for bursts of rapid change during the evolution of pituitary growth hormone

Pituitary growth hormone shows a pattern of molecular evolution in which occasional bursts of rapid change are imposed on a slow basal rate. It is suggested that these bursts of rapid evolution are a consequence of acquisition by this protein hormone of a secondary function, the importance of which varies. As the function of the hormone switches to accommodate the changes in role, its structure will also alter, adapting it to acquisition or loss of the secondary function. Several rounds of such "function switching" could give a substantial change in structure (the sum of several small changes) with little overall change in function. A similar process could underlie rapid bursts of evolution in other proteins.

Use of two view mammography compared with one view in the detection of small invasive cancers: further results from the National Health Service breast screening programme

OBJECTIVE

To examine further the effect of using two view mammography in comparison with one view mammography in the detection of small (< 15 mm) invasive cancers for programmes in the National Health Service breast screening programme (NHSBSP). The study is in two parts: first the effect on the small invasive cancer detection rate for programmes that changed from using one view to two views for first (prevalent) screens, and secondly the effect on the small invasive cancer detection rate for programmes that used two views for subsequent (incident) screens compared with programmes that used one view.

SETTING

Screening programme data from the NHSBSP.

METHODS

Data were collated from all screening programmes in the United Kingdom on standard "Korner" returns (KC62 forms) for the screening years 1 April 1994 to 31 March 1995 and 1 April 1995 to 31 March 1996. The comparison between one and two view mammography was made using indirectly age standardised invasive cancer detection rates.

RESULTS

For prevalent (first) screens, programmes changing from one view mammography in 1994/95 to two views in 1995/96 reported a 45% (95% confidence interval (CI) 25% to 68%) increase in the detection of invasive cancers of < 15 mm. In comparison, programmes that were already using two views in 1994/95 showed no change in 1995/96. For incident (subsequent) screens the small number of programmes that have opted to use two views reported 25% (95% CI 1% to 55%) more invasive cancers of < 15mm than programmes using one view in 1995/96, and 42% (95% CI 11% to 81%) more in 1994/95. CONCLUSIONS--These results confirm the benefit of using two view mammography in the detection of small invasive cancers, and provide evidence that this effect is seen in subsequent screens as well as the first screen.

The molecular evolution of vertebrate growth hormones: a pattern of near-stasis interrupted by sustained bursts of rapid change

It has been demonstrated previously that in mammals the evolution of pituitary growth hormone shows an unusual pattern, with an underlying slow rate and at least two sustained bursts of rapid evolution (in the artiodactyls and primates), during which the rate increased at least 25-fold. It is demonstrated here that a similar pattern applies for growth hormone evolution throughout the vertebrates, with a basal rate similar to that seen in mammals, but bursts of rapid evolution in the amphibia and the elasmobranchs, and several bursts in the teleosts. The placental growth-hormone-like proteins of primates show a similar pattern. It is argued that the bursts of evolution seen for growth hormone are a consequence of selection and that this may reflect changes in the functions of the hormone additional to its basic growth-promoting actions.

A comparison of two view and one view mammography in the detection of small invasive cancers: results from the National Health Service breast screening programme

OBJECTIVE

To examine the effect of using two view mammography in comparison with one view mammography in the detection of small (< 15 mm) invasive cancers.

SETTING

Screening programme data from National Health Service breast screening programme (NHSBSP).

METHODS

Data were collated from all screening programmes in the United Kingdom on standard "Korner" returns (KC62 forms) for the screening year 1 April 1994 to 31 March 1995. The comparison of invasive cancer detection rates by programmes using one and two view mammography with indirectly age standardised invasive cancer detection rates.

RESULTS

Programmes using two views for women attending their prevalent screen (first screen) in the NHSBSP detected 3% more non-invasive/microinvasive cancers, 7% more large invasive cancers (> or = 15 mm), and 42% more small invasive cancers (< 15 mm) than programmes using one view mammography.

CONCLUSIONS

The success of the screening programme depends largely on the ability of individual programmes to detect small invasive cancers. The results suggest that the benefit of using two view mammography is largely in the increased detection of these cancers.

Classifying interval cancers

No definitive way of classifying interval breast cancers (cancers presenting between screening rounds) has been determined, yet their number and classification forms one of the quality assurance (QA) standards for the National Health Service Breast Screening Programme (NHSBSP). This study was undertaken to identify how different screening centres undertake this process, and to compare the classifications obtained when a test set of mammograms was reviewed using three different methods. A questionnaire was sent to the 17 Regional UK breast screening QA centres. Twelve (80%) of the 15 centres completing the questionnaire had a formal method for reviewing interval cancers. Five of these (33%) attempted to simulate screening by mixing the interval cancers with other screening films. In 11 (73%) centres, a group (size range 3-14) of radiologists was involved. In a simulated film viewing exercise we assessed whether different methods of classification would alter the number of interval cancers classified as false negative (where an abnormality suspicious of malignancy can be identified on review of the original screening films). Six radiologists reviewed a set of 50 interval cancers by three different methods: independent reading of the interval cancers mixed with screening mammograms; independent reading of the interval cancers on their own; and finally a consensus opinion of the interval cancers alone using the films taken at diagnosis. No discussion or review of these cases had taken place prior to the study. The number of interval cancers classified as false negative increased by 10% when they were reviewed in isolation compared to review among 'normal' screening films. The false negative rate varied widely (4% to 56% P < 0.01) depending on the criteria required to fulfil a false negative interval cancer classification--whether only one, a majority, or all of the radiologists were required to see the abnormality on the original screening films. In order for inter-unit and regional comparisons to be useful, a standard review method of mixing the interval cancer films with normal screening films and using a consensus opinion by a minimum of three external reviewers is suggested.

Cloning and characterisation of the rabbit growth hormone-encoding gene

The gene encoding growth hormone (GH) has been cloned from a rabbit genomic library, and its sequence has been determined. The rabbit GH gene is similar to other mammalian GH, being comprised of five exons and four introns. As in rodents and artiodactyls, the rabbit GH occurs as a single gene, with no evidence for a cluster of GH-like genes, as is found in primates. The amino acid sequence of rabbit GH is similar to that of pig GH and other conserved mammalian GH, and, like these, differs markedly from the available sequences of ruminant and primate GH. This provides further support for the idea that, in mammals, GH show a slow underlying rate of evolution which has increased markedly on at least two occasions.

A novel RNA motif for neomycin recognition

BACKGROUND

Antibiotics can interfere with RNA activity. Translation of RNA by the prokaryotic ribosome, self-splicing of group I introns, HIV replication and hammerhead ribozyme cleavage are inhibited by the aminoglycoside neomycin B. To explore the molecular basis by which small molecules such as antibiotics inhibit RNA function, we undertook an in vitro selection to obtain a variety of RNA molecules with the capacity to recognize neomycin.

RESULTS

The majority of the RNA molecules selected to specifically bind neomycin share a region of nucleotide sequence homology. From chemical probing and covariations among different clones we show that in all sequences this region folds into a hairpin structure, which from footprinting and partial alkaline hydrolysis experiments is shown to be the neomycin-binding site. Neomycin is recognized with high affinity (Kd approximately equal to 100 nM) and high specificity (> 100-fold higher affinity for neomycin than for paromomycin).

CONCLUSIONS

The fact that RNAs containing the consensus sequence, as well as sequences that display variations within this region, specifically recognize neomycin suggests that a structural motif rather than a particular nucleotide sequence is required for neomycin recognition. We propose that a hairpin stem-loop structural motif, which might feature a widened major groove, may be a prerequisite for neomycin recognition. This structural pattern can be extrapolated to other natural neomycin-responsive RNAs.

The effect of changes in nucleotide sequence coding for the N-terminus on expression levels of ovine growth hormone variants in Escherichia coli

The expression levels of coding sequences for pituitary growth hormone, introduced into Escherichia coli by genetic manipulation techniques, vary markedly according to the precise sequence introduced. In order to understand the basis of this variation more fully, we have studied the relationship between the level of expression in E. coli of a series of ovine growth hormone variants and the nucleotide sequences coding for their N-terminal regions. Sequence variation resulted from the introduction of deletions, or site-directed mutations, into a plasmid containing the coding sequence for ovine growth hormone preceded by the initiation codon and 25 bases derived from beta-galactosidase or linker regions of plasmid pUC8. The expression levels of the variants varied from less than 0.01% to over 34% of the total cell protein, indicating that changes in the nucleotide sequence close to the initiation codon had a marked effect on expression level. The results of a comparison of closely related sequences in pairs of plasmids giving poor or good expression are consistent with the hypothesis that poor translation of growth hormone mRNAs is caused by the presence of secondary structures close to the initiation codon. Secondary structures are identified that appear to explain the variation in expression levels.

Extinction of dinosaurs: a possible novel cause

A novel cause of mass extinction of fauna close to the (K/T) Boundary is suggested. A large amount of non-protein amino acids (AIB and ISOVAL) has been observed close to this event. It is speculated that these amino acids may be toxic and are responsible for the extinction. The toxicity level is estimated for this suggestion to be true and experimentalists are encouraged to test this level of toxicity for the amino acids.

Mammographic film density and detection of small breast cancers

From its inception, the UK National Breast Screening Programme (NHSBSP) has recognized that optimum image quality of the mammographic screening test is a key objective. The overall optical density of the mammography film is one of the factors expected to have a significant effect on the image quality of the mammogram with the potential to influence cancer detection. In a previous review of the performance of mammography equipment in the NHSBSP, it was observed that there was a very wide range in the mammographic film densities used at different breast screening centres. In this study a mammography test object was used to show experimentally that, for a typical mammography system, image quality increased substantially with increased film density. Summary data was therefore requested from radiologists in the NHSBSP on the rate of detection of small invasive cancers (diam. < or = 10 mm) and the typical film density used during that year. Proforma were completed for 61 annual sets of results from 31 screening centres involving over 500,000 women. Where centres reported using film densities of less than 1.2D the average small cancer detection rate was 0.12% +/- 0.01%, as compared to an average of 0.17% +/- 0.01% for centres using higher film densities. The results indicate that there is a need for national guidelines in the setting of film densities, and a range for target film densities of 1.4D to 1.8D has been suggested. Attention to optimizing image quality by increasing film density is of particular importance to any screening centre where film densities of less than 1.2D are used, as there may be the potential to increase the detection of small breast cancers by as much as 50%.

Variable evolutionary rates in the molecular evolution of mammalian growth hormones

In mammals pituitary growth hormone (GH) shows a slow basal rate of evolution (0.22 +/- 0.03 x 10(-9) substitutions/amino acid site/year) which appears to have increased by at least 25-50-fold on two occasions, during the evolution of primates (to at least 10.8 +/- 1.3 x 10(-9) substitutions/amino acid site/year) and artiodactyl ruminants (to at least 5.6 +/- 1.3 x 10(-9) substitutions/amino acid site/year). That these rate increases are real, and not due to inadvertent comparison of nonorthologous genes, was established by showing that features of the GH gene sequences that are not expressed as mature hormone do not show corresponding changes in evolutionary rate. Thus, analysis of non-synonymous substitutions in the coding sequence for the mature protein confirmed the rate increases seen in the primate and ruminant GHs, but analysis of nonsynonymous substitutions in the signal peptide sequence, synonymous substitutions in the coding sequence for signal peptide or mature protein, and 5' and 3' untranslated sequences showed no statistically significant changes in evolutionary rate. Evidence that the increases in evolutionary rate are probably due to positive selection is provided by the observation that in the cases of both ruminant and primate GHs the periods of rapid evolution were followed by a return to a slow rate similar to the basal rate seen in other mammalian GHs.(ABSTRACT TRUNCATED AT 250 WORDS)

The NAM1 protein (NAM1p), which is selectively required for cox1, cytb and atp6 transcript processing/stabilisation, is located in the yeast mitochondrial matrix

The NAM1 nuclear gene was shown to control the stability and/or processing of mitochondrial transcripts of the cytochrome b, cytochrome oxidase subunit I and ATP synthase subunit VI genes [Groudinsky O., Bousquet I., Wallis M. G., Slonimski, P. P. & Dujardin G. (1993) Mol. Gen. Genet. 240, 419-427]. In order to better understand the mode of action of the NAM1 gene product, we have examined its intracellular fate. A fusion plasmid enabling bacterial over-expression of the corresponding protein-A-NAM1 cognate was constructed and subsequently employed as an antigen to raise polyclonal antibodies. These antibodies specifically recognise a 50-kDa protein which purifies along with the mitochondria and corresponds to NAM1p. Submitochondrial localisation experiments show that NAM1p is a soluble protein, located interior to the mitoplasts. Matricial location is a strong argument in favour of a direct interaction of NAM1p with particular mitochondrial transcripts and leads us to propose a model in which NAM1p could be an RNA-convoying protein stabilising and directing mitochondrial transcripts towards the inner face of the inner membrane where translation and assembly seem to occur.

Preparation and characterization of a recombinant DNA-derived ovine growth hormone variant internally labelled with sulphur-35

125I-Labelled polypeptide hormones have been extremely valuable for radioimmunoassays, receptor-binding studies and investigation of the processing and metabolism of hormones. However, such externally labelled material has the disadvantage that addition of one or more iodine atoms may alter the properties of the polypeptide. Furthermore, for studies on hormone metabolism and processing, the label may become separated from the hormone or its main breakdown products. Use of internally labelled polypeptides produced by biosynthesis can avoid such problems, but previously such material has usually been of low specific radioactivity, and unsuitable for many purposes. Here we describe the development of a procedure for the production of an internally labelled ovine GH analogue (oGH1) using a plasmid produced by recombinant DNA methods and expression in Escherichia coli. Bacteria were grown in medium containing a low sulphate concentration, and then incubated in medium containing 35SO4(2-) as the sole sulphur source. Under these conditions, the bacteria incorporated 35S into proteins including GH. Purification of such material required considerable modification of previously described methods, because of the need to handle very small amounts of highly radioactive material. The bacteria were lysed using lysozyme, and inclusion bodies were solubilized using 6 M guanidinium chloride. [35S]oGH1 was renatured and then purified by gel filtration on Sephacryl S-100, followed by immunoaffinity chromatography and a second gel filtration step. Material prepared in this way had a specific radioactivity of 6-27 microCi/micrograms, and showed high 'bind-ability' to polyclonal and monoclonal antibodies and to receptors. 35S-Labelled material bound to receptors more effectively than 125I-labelled GH and showed improved stability.(ABSTRACT TRUNCATED AT 250 WORDS)

Complex sclerosing lesions (radial scars) of the breast can be palpable

Complex sclerosing lesion (CSL)/radial scar and carcinoma of breast can both present mammographically as stellate lesions. The mammographic features used to distinguish these two entities are reported as being unreliable. All reports to date indicate that CSLs are not palpable. Of the 54,407 women screened in the first 2 1/2 years of the Warwickshire, Solihull and Coventry Breast Screening Service, 24 histologically-proven CSLs were identified. This represents an incidence of 0.04%. In six (25%) of these patients a corresponding clinically-palpable abnormality was identified. We found no imaging or histological features that differentiated the palpable lesions from the impalpable lesions. It is important not to assume that a palpable stellate lesion is a carcinoma.

The NAM1/MTF2 nuclear gene product is selectively required for the stability and/or processing of mitochondrial transcripts of the atp6 and of the mosaic, cox1 and cytb genes in Saccharomyces cerevisiae

The NAM1/MTF2 gene was firstly isolated as a multicopy suppressor of mitochondrial splicing deficiencies and independently as a gene of which a thermosensitive allele affects mitochondrial transcription in organello. To determine which step in mitochondrial RNA metabolism is controlled in vivo by the NAM1 gene, mitochondrial transcripts of seven transcription units from strains carrying an inactive nam1::URA3 gene disruption in various mitochondrial genetic backgrounds were analysed by Northern blot hybridisations. In a strain carrying an intron-containing mitochondrial genome, the inactivation of the NAM1 gene led to a strong decrease in (or total absence of) the mosaic cytb and cox1 mRNAs and in transcripts of the atp6-rf3/ens2 genes, which are co-transcribed with cox1. Neither the accumulation of unspliced cytb or cox1 pre-mRNAs, nor that of excised circular intron molecules of ai1 or ai2 were observed, but the abundance of the bi1 and ai7 lariats was comparable to that observed in the wild-type strain, thus demonstrating that transcription of the cytb and cox1 genes does occur. In strains carrying the intron-less mitochondrial genome with or without the rf3/ens2 sequence, wild-type amounts of cytb and cox1 mRNAs were detected while the amount of the atp6 mRNA was always strongly decreased. The abundance of transcripts from five other genes was either slightly (21S rRNA) or not at all (cox2, cox3, atp9 and 15S rRNA) affected by the nam1 inactivation.(ABSTRACT TRUNCATED AT 250 WORDS)

Remarkably high rate of molecular evolution of ruminant placental lactogens

The sequences of ovine and bovine placental lactogens (based on published cDNA sequences) are remarkably different, indicating a very rapid rate of evolution. Analysis of the cDNA sequences indicates that the rate of nonsynonymous substitution in these proteins is considerably greater than the rate of synonymous substitution. This is an unusual situation, which suggests that the observed rapid rate of evolution is due to incorporation of adaptive rather than neutral mutations.

A review of false negative mammography in a symptomatic population

A review of the mammograms of 871 patients with breast cancer from a symptomatic clinic performed at the General Hospital, Birmingham between 1980 and 1988 revealed an overall false negative rate of 8.6%. There has been a steady fall in the number of cancers missed per year from the commencement of review, and this reduction has been more consistent with improvements in radiographic equipment and technique, particularly the introduction of a radiographic grid. In half of the cases the tumour was missed because no radiological abnormality was detectable, even on reviewing the films, and this rate has remained remarkably stable over the study period, emphasizing the importance of a clinical examination in symptomatic women. Comparison of the histological diagnoses revealed similar percentages of ductal carcinomas, 89.6% in the true positive group compared with 85% in the false negative group. Of the false negative carcinomas, 5.5% were medullary tumours compared to 0.8% in the true positive group.

Immunocytochemical and morphometric studies of mammotrophs, somatotrophs and somatomammotrophs in sheep pituitary cell cultures

Alterations occurring when sheep anterior pituitary cells are placed in culture for 4 days were studied using electron microscopy and immunogold labelling. The majority of cells present showed marked morphological changes during culture, with degranulation and development of extensive rough endoplasmic reticulum. The proportions of somatotrophs and mammotrophs, as identified by immunogold labelling, fell during culture. The majority (70%) of somatotrophs showed relatively little degranulation but the remainder were extensively degranulated after 4 days in culture, suggesting two subpopulations of this cell type. Conversely, most (80%) of the mammotrophs showed extensive degranulation after culture, but one-fifth remained heavily granulated, suggesting that mammotrophs too are heterogeneous. The proportion of cells labelling for both GH and prolactin (somatomammotrophs) increased during culture to about 3% of the cells present, compared with less than 0.2% of all cells before culture.

Growth, body composition, hormonal and metabolic status in lambs treated long-term with growth hormone

The effect of long-term (10 weeks) treatment with growth hormone (GH) was investigated in twin lambs, one sibling being a control and the other treated with GH (0.1 mg/kg live weight per d). The lambs were fed on a concentrate-grass cube (9:1 w/w) diet at a daily rate of 40 g fresh weight/kg live weight. The average daily live-weight gain of the GH-treated lambs was 36% greater than that of the controls (307 v. 225 g/d, P less than 0.01). The carcass composition of the GH-treated lambs changed: fat content was decreased (P less than 0.01) and protein content was increased (P less than 0.05) when expressed relative to carcass dry matter. The absolute weights and the weights when expressed relative to fleece-free empty body of some muscles were significantly increased in GH-treated lambs. The mean retention times of both particulate- and liquid-phase components of the digesta were unchanged by GH treatment, when calculated for the rumen or for the entire gastrointestinal tract. The feed conversion ratio was significantly greater (P less than 0.01) in GH-treated lambs compared with controls. Nitrogen retained per g N intake was also significantly increased (P less than 0.05) by GH treatment. Plasma urea concentrations were decreased (P less than 0.05) and glucose concentrations were increased (P less than 0.01) in GH-treated lambs, whereas non-esterified fatty acid concentrations were unchanged. Plasma insulin and total insulin-like growth factor-1 concentrations progressively increased in GH-treated lambs as treatment time continued. They were significantly correlated after week 4 of treatment. Two types of hepatic GH-binding site were detected, with high and low affinities for GH. The capacities of both binding sites were significantly increased (P less than 0.05) in GH-treated lambs when expressed per unit microsomal protein but, when expressed per liver, only the capacity of the high-affinity site was increased.

Induction of lactogenic receptors in liver of hypophysectomized rats treated with bovine growth hormone-monoclonal antibody complexes

Male hypophysectomized rats treated with bovine (b)GH-monoclonal antibody complexes showed enhanced weight gain compared with animals treated with bGH alone over a 12-day treatment period. Liver microsomes prepared from animals showing enhanced weight gain exhibited increased specific binding of human (h)GH. Studies on the specificity of these binding sites showed that they were lactogenic, 125I-labelled hGH being displaced by ovine prolactin, but not by non-mammalian growth hormones. In this respect they were similar to lactogenic binding sites in the liver of pregnant rats. Monoclonal antibodies to hGH blocked binding to lactogenic receptors to different extents. The pattern of such inhibition was similar, but not identical, for the receptors induced in hypophysectomized rats and those from pregnant rat liver. The evidence available suggests that the lactogenic receptors induced by bGH-monoclonal antibody complexes are not directly involved in the enhancement of growth.

Isolation and partial characterization of an extradiol non-haem iron dioxygenase which preferentially cleaves 3-methylcatechol

A purification procedure has been developed for an extradiol dioxygenase expressed in Escherichia coli, which was originally derived from a Pseudomonas putida strain able to grow on toluidine. Physical and kinetic properties of the enzyme have been investigated. The enzyme has a subunit Mr of 33,500 +/- 2000 by SDS/polyacrylamide-gel electrophoresis. Gel filtration indicates a molecular mass under non-denaturing conditions of 120,000 +/- 20,000. The N-terminal sequence (35 residues) of the enzyme has been determined and exhibits 50% identity with other extradiol dioxygenases. Fe(II) is a cofactor of the enzyme, as it is for other extradiol dioxygenases. The reactivity of this enzyme towards catechol and methyl-substituted catechols is somewhat different from that seen for other catechol 2,3-dioxygenases, with 3-methylcatechol cleaved at a higher rate than catechol or 4-methylcatechol. Km values for these substrates with this enzyme are all around 0.3 microM. The enzyme exhibits a bell-shaped pH profile with pKa values of 6.9 +/- 0.1 and 8.7 +/- 0.1. These results are compared with those found for other extradiol dioxygenases.

Purification and properties of a recombinant DNA-derived ovine growth hormone analogue (oGH1) expressed in Escherichia coli

An Escherichia coli JM109 clone containing a plasmid, pOGHe101, based on pUC8 and the ovine GH (oGH) cDNA sequence, showed very high expression (up to 25% of total cell protein) of an oGH analogue (oGH1) after induction. oGH1 was found in the particulate fraction of induced bacteria, where electron-dense granules could be seen by electron microscopy. A simple method for the purification of oGH1 is described. The particulate fraction isolated from sonicated bacteria was dissolved in 6M guanidinium chloride containing dithiothreitol. After threefold dilution the proteins were reoxidized by gentle stirring overnight in air. Soluble renatured protein, recovered after dialysis, was further purified by ion-exchange and gel-filtration chromatography. Purified oGH1 had an Mr of 22,000, an isoelectric point of about 6.7 and an N-terminal sequence corresponding to that of oGH, with an extension of eight amino acids replacing the N-terminal alanine. oGH1 behaved similarly to authentic bovine GH in a radioimmunoassay, a radioreceptor assay and a weight-gain assay in hypophysectomized rats. Thus the renatured hormone appears to be correctly folded and the N-terminal extension has little or no effect on biological activity.

Occurrence of rare somatomammotrophs in ovine anterior pituitary tissue studied by immunogold labelling and electron microscopy

Prolactin and GH are distinct hormones that have been conventionally thought to be produced and secreted by separate cells in the anterior pituitary gland. Recently it has been suggested that some cells (somatomammotrophs) may secrete both hormones. We have examined the occurrence of somatomammotrophs in sheep anterior pituitary tissue using immunogold labelling. Of a number of procedures used, double labelling using first antibodies raised in different species proved the least susceptible to apparent co-localization of hormones due to artifacts. Using this approach it was shown that a large proportion of the cells in the sheep anterior pituitary glands examined were mammotrophs or somatotrophs, showing no significant co-localization of GH and prolactin. Of 1800 cells examined, only two were somatomammotrophs. One of these, from a female animal, contained GH and prolactin in different granules within the same cell. The other, from a male animal, showed co-localization of these two hormones within the same granules.

Effects of pretreatment with tetradecanoyl phorbol acetate on regulation of growth hormone and prolactin secretion from ovine anterior pituitary cells

Tetradecanoyl phorbol acetate (TPA) stimulates growth hormone (GH) and prolactin secretion from ovine anterior pituitary cells. Pretreatment of the cells with TPA abolishes this effect, presumably due to down-regulation of protein kinase C. Such pretreatment did not alter effects of thyrotropin-releasing hormone or dopamine on prolactin secretion, suggesting no involvement of protein kinase C. Pretreatment with TPA attenuated actions of GH-releasing hormone on GH release (but not actions on cyclic AMP levels), possibly due to depletion of cellular stores of GH. Such pretreatment also attenuated inhibition of GH release by somatostatin, possibly due to phosphorylation of receptors or associated proteins by protein kinase C.

Cloning, sequence and expression in Escherichia coli of cDNA for ovine pregrowth hormone

cDNA prepared from mRNA from ovine anterior pituitary glands was cloned in Escherichia coli and the sequence of a clone encoding the full coding sequence of ovine pregrowth hormone (preGH) determined. The predicted sequence for ovine GH agrees with that determined previously on the protein, except that residue 99 is asparagine rather than aspartic acid. The cDNA sequence also accords with one of the two genomic sequences for the ovine GH gene that have been reported. Expression plasmids using trp and lac promoters were constructed which allowed expression at low levels of ovine preGH in E. coli, as detected by immunoblotting and immunoassay.