Estimation of unbiased recombination values in the presence of misclassification of a trait using RFLP maps

The effect of misclassification of phenotypes of a trait on the estimation of recombination value was investigated. The effect was larger for closer linkage. If a locus is dominant and linked with the misclassfied trait locus in the repulsion phase, then the effect on the recombination value between the two loci is largest. A method for estimating the unbiased recombination value and the misclassification rate using maximum likelihood associated with an EM algorithm is also presented. This method was applied to a numerical example from rice genome data. It was concluded that the present method combined with the metric multi-dimensional scaling method is useful for the detection of misclassified markers and for the estimation of unbiased recombination values.

[CuZn-SOD determination of sera in patients with rheumatic diseases]

Superoxide anion (O2.-) plays an important part in reactive oxygen species (ROS). In order to explore its effect on the pathogenesis of rheumatic diseases, authors had determined CuZn-SOD contents of sera in 132 subjects involving the patients of rheumatic diseases (SLE, RA, etc), non-rheumatic diseases and normal controls by using enzyme linked immunosorbent assay (ELISA). The results showed the followings: CuZn-SOD contents of 27 normal subjects: 98.80 +/- 20.74 ng/ml (x +/- s); that of 27 non-rheumatic diseases cases: 72.24 +/- 16.60 ng/ml (x +/- s); of 22 SLE cases: 56.56 +/- 19.27 ng/ml (x +/- s); of 27 RA cases: 61.56 +/- 20.53 ng/ml (x +/- s); of 29 other rheumatic diseases cases: 68.97 +/- 17.79 ng/ml (x +/- s). Statistical test was made: both CuZn-SOD contents of rheumatic disease and non-rheumatic disease were lower than that of normal subjects with more significant difference (P < 0.001); compared with that of non-rheumatic diseases patients, SLE cases had significant difference (P < 0.01); RA cases had significant difference (P < 0.05); other cases of rheumatic diseases had no statistical differrence (P > 0.05). Above results suggest that superoxide anion is a non-specific inflammatory mediator which contributes to disorders with inflammatory damages (rheumatic or non-rheumatic diseases), where CuZn-SOD content tested was obviously lower than normal subjects; among the rheumatic disease patients, CuZn-SOD contents of the sera of SLE patients were the lowest because of its more autoimmune antibody, more severe inflammatory and immunological reaction. This work laid the theoretical and experimental foundation for the clinical application of exogenous CuZn-SOD in the treatment of rheumatic diseases. Combined use of CuZn-SOD scavengers may get better result because of the complexibility of ROS inflammatory mechanism.

Arbitrarily primed DNA fingerprinting for phylogenetic reconstruction in vertebrates: the Xiphophorus model

Arbitrarily primed PCR (AP-PCR or RAPD) is a technique for producing species-specific DNA fingerprints. We tested the utility of AP-PCR as a source of phylogenetically informative characters in three separate experiments, using fishes of the genus Xiphophorus. We chose Xiphophorus as a standard of comparison, because evolutionary relationships within the genus have been studied repeatedly using a variety of techniques. We compared our results to a "classical" phylogenetic hypothesis synthesized from studies using morphological, pigmentation, and allozyme characters, and to a recent conflicting hypothesis constructed from DNA sequence data. The sequence-based hypothesis places the southern swordtail Xiphophorus clemenciae squarely within the platyfish, whereas the classical hypothesis separates the two groups. In addition, the two hypotheses differ in their clustering of species of northern swordtails. Our findings are in close accord with the classical hypothesis. Our results allow the strongest phylogenetic hypothesis yet for Xiphophorus and demonstrate the utility of AP-PCR for studying species relationships within vertebrate genera.

[Karyological studies on the fruit of Gardenia jasminoides Ellis]

This paper reports the karyological studies on the fruit of Gardenia jasminoides and G. jasminoides var. grandiflora. The chromosome numbers are 2n = 22 and the places of centromere are metacentric and submedian. The fruit of G. jarminoides is more primary than Gardenia jarminoidce var. grandiflora in karyotype.

Mapping Influence Regions in Heirarchical Clustering

Three-dimensional response surface plots arc presented for several hierarchical clustering methods and simulated core group data structures. The response surface represents the relative influence of the corresponding coordinate location in the bivariate data space on the clustering of the core groups. lnfluence is defined as a change in the clustering of the core groups when an element situated at a specified coordinate location is removed from the data set. The nature of the influence, whether beneficial or detrimental to the clustering process, can be determined from the plots. The influence plots revealed substantial differences between clustering methods. The influence patterns also explain some of the results found in previous validation research on clustering methods. The results have significant implications on the choice of clustering methods to be used in empirical research.

Cloning and chromosomal mapping of three novel genes, GPR9, GPR10, and GPR14, encoding receptors related to interleukin 8, neuropeptide Y, and somatostatin receptors

We employed the polymerase chain reaction and genomic DNA library screening to clone novel human genes, GPR9 and GPR10, and a rat gene, GPR14. GPR9, GPR10, and GPR14 each encode G protein-coupled receptors. GPR10 and GPR14 are intronless within their coding regions, while GPR9 contains at least one intron. The receptor encoded by GPR9 shares the highest identity with human IL-8 receptor type B (38% overall and 53% in the transmembrane regions), followed by IL-8 receptor type A (36% overall and 51% in the transmembrane domains). GPR10 encodes a receptor that shares highest identity with the neuropeptide Y receptor (31% overall and 46% in the transmembrane domains). The receptor encoded by GPR14 shares highest identity with the somatostatin receptor SSTR 4 (27% overall and 41% in the transmembrane domains). Fluorescence in situ hybridization analysis localized GPR9 to chromosome 8p11.2-p12 and GPR10 to chromosome 10q25.3-q26.

The cloning and chromosomal mapping of two novel human opioid-somatostatin-like receptor genes, GPR7 and GPR8, expressed in discrete areas of the brain

Following the cloning of the opioid receptors mu, kappa, and delta, we conducted a search for related receptors. Using oligonucleotides based on the opioid and also the structurally related somatostatin receptors, we amplified genomic DNA using the polymerase chain reaction and isolated fragments of novel G protein-coupled receptor genes. Two of these gene fragments designated clones 12 and 11 were used to isolate the full-length genes. The intronless coding sequences of these genes, named GPR7 and GPR8, shared 70% identity with each other, and each shared significant similarity with the sequences encoding transmembrane regions of the opioid and somatostatin receptors. GPR7 was mapped to chromosome 10q11.2-q21.1 and GPR8 to chromosome 20q13.3. Northern blot analysis using human mRNA demonstrated expression of GPR7 mainly in cerebellum and frontal cortex, while GPR8 was located mainly in the frontal cortex. In situ hybridization revealed expression of GPR7 in the human pituitary. A partial sequence of the mouse orthologue of GPR7 was obtained, and in situ hybridization demonstrated expression in discrete nuclei of brain, namely suprachiasmatic, arcuate, and ventromedial nuclei of hypothalamus. A stable cell line expressing the GPR7 gene was created, but expression levels of the receptor were low. The available pharmacology indicated binding to several opioid drugs such as bremazocine, levorphanol, and beta-FNA, but not to the opioid receptor subtype-selective mu, delta, or kappa agonists.

Diminished Ca2+ sensitivity of skinned cardiac muscle contractility coincident with troponin T-band shifts in the diabetic rat

We have measured the apparent Ca2+ sensitivities of force development in skinned cardiac trabeculae at different sarcome lengths together with shifts in troponin (Tn) T subunits on specimens from the same hearts and drawn insights into the pathogenesis of myocardial dysfunction in the diabetic rat. The Ca(2+)-force relations were measured at a long (2.4-microns) and a short (1.9-microns) sarcomere length. In disease, compared with the control condition, the apparent Ca2+ sensitivity was greatly diminished at a sarcomere length of 1.9 microns but not affected at all at the long length (2.4 microns). We also examined the alterations in contractile regulatory proteins TnT and TnI by both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blots. The TnI band was largely unperturbed, but major changes were discerned in TnT. The normal rat heart indicated two major bands (TnT1 and TnT2) and a faint third band (TnT3); in the diabetic rat heart, there was a significant shift in intensity from TnT1 to TnT3. Since myosin isozyme shifts also accompany diabetes in the rat, we used a prototypical hypothyroid rat as well to evaluate the myosin influence in the length-induced effects on Ca2+ sensitivity. Myosin shifts during hypothyroidism were unaccompanied by significant changes in TnT, and there were also no length-dependent modifications in Ca2+ sensitivity. The findings raise the possibility that diabetic Ca(2+)-sensitivity changes in the myocardium are coupled with TnT alterations. A plausible explanation is offered whereby these TnT alterations modify the length dependence of Ca2+ sensitivity.

Isolation of three novel human genes encoding G protein-coupled receptors

We have cloned and mapped the chromosomal location of three novel human genes encoding G protein-coupled receptors that we have named GPR6, GPR5, and GPR4. The entire coding region for each of these genes was contained on single exons. Gene GPR6 encoded a receptor that shared closest identity (71% in the transmembrane regions) with the human orphan receptor GPR3 and was localized to chromosome 6 (q21-q22.1). Northern blot analysis revealed that GPR6 transcripts were abundant in the human putamen and to a lesser extent in the frontal cortex, hippocampus, and hypothalamus. Gene GPR5 encoded a receptor that most closely resembled the orphan receptor RBS11 (48% in the transmembrane regions) and the MIP 1 alpha/RANTES receptor (45% in the transmembrane regions) and was localized to chromosome 3 (p21.3-p21.1). Gene GPR4 shared identity (40% in the transmembrane regions) with the human platelet-activating factor receptor and was localized to chromosome 19 (q13.2-q13.3).

Mapping studies of two G protein-coupled receptor genes: an amino acid difference may confer a functional variation between a human and rodent receptor

We recently isolated two orphan human G protein-coupled receptor genes designated GPR1 and GPR6. The gene GPR1 was shown to be transcribed abundantly but only in the hippocampus. Here we report the cloning of the rat GPR1 gene and report the absence of expression in hippocampus, demonstrating a functional variation for this receptor in these two species. The evolutionary history of an important sequence difference in the gene GPR1 in primate and rodent species has been examined. In contrast extensive mapping of gene GPR6 mRNA in rat brain was in keeping with the described distribution in human brain.

Distinct distributions of mu, delta and kappa opioid receptor mRNA in rat brain

We present a comprehensive comparison of the anatomical distributions of the cloned mu, delta and kappa opioid receptor mRNA in rat brain. Northern blot analysis revealed that mRNA species encoding the three receptors differed in size and were differentially localized in brain regions. In peripheral tissues analyzed, the 3 mRNA species were detected only in the spinal cord. The distributions of mu, delta and kappa receptor mRNA in rat brain were examined by in situ hybridization histochemistry using gene-specific probes. Mu receptor mRNA was predominately localized to thalamic, brainstem and reticular core nuclei and was highest in the habenular and thalamic nuclei. In contrast, kappa receptor mRNA was expressed in hippocampus including dentate gyrus, hypothalamic and some thalamic nuclei and also present in cortex, caudate putamen, olfactory tubercle and nucleus accumbens. Delta receptor mRNA was prominent in cerebral cortex, olfactory tubercle, hippocampus, caudate putamen and nucleus accumbens. These results show that the mRNA distribution for each opioid receptor subtype in brain is unique and correlate well with the known distribution of the corresponding opioid receptor binding sites.

Interactions among regulators of RNA abundance characterized using RNA fingerprinting by arbitrarily primed PCR

Using RNA fingerprinting by arbitrarily primed PCR it is possible to infer convergent transcript regulatory pathways from the coordinate behavior of subsets of anonymous transcripts without cloning any genes. The number of transcripts in each response category can be estimated. The same may be true for differential display. We demonstrate these claims by treating a cell line with two known modulators of RNA abundance, transforming growth factor-beta (TGF beta) and cycloheximide (CX), used together and alone. The responses of over 1700 anonymous transcripts were monitored under these three conditions and in an untreated control. Eight of the twenty-seven [3(3)] possible transcript response categories were observed among 86 differentially expressed transcripts. For example, CX stabilizes or induces as many as 2.7% of transcripts of which about one third do not accumulate when TGF beta is also present. This intersection may reflect CX stabilization or induction of an important class of RNAs that otherwise usually have short half-lives. We predict that RNAs in this class constitute the majority of transcripts targeted for rapid down regulation in response to TGF beta and perhaps most other natural transcriptional modulators.

Cloning of human genes encoding novel G protein-coupled receptors

We report the isolation and characterization of several novel human genes encoding G protein-coupled receptors. Each of the receptors contained the familiar seven transmembrane topography and most closely resembled peptide binding receptors. Gene GPR1 encoded a receptor protein that is intronless in the coding region and that shared identity (43% in the transmembrane regions) with the opioid receptors. Northern blot analysis revealed that GPR1 transcripts were expressed in the human hippocampus, and the gene was localized to chromosome 15q21.6. Gene GPR2 encoded a protein that most closely resembled an interleukin-8 receptor (51% in the transmembrane regions), and this gene, not expressed in the six brain regions examined, was localized to chromosome 17q21.1-q21.3. A third gene, GPR3, showed identity (56% in the transmembrane regions) with a previously characterized cDNA clone from rat and was localized to chromosome 1p35-p36.1.

Maternal serum free alpha- and free beta-human chorionic gonadotrophin in pregnancies with insulin-dependent diabetes mellitus: implications for screening for Down's syndrome

A study was performed to investigate the concentrations of the alpha and beta free sub-units of human chorionic gonadotrophin (free alpha-hCG and free beta-hCG) in maternal serum between 15 and 22 weeks of pregnancy in 126 pregnancies among 92 women with insulin-dependent diabetes mellitus (IDDM). Each IDDM pregnancy was matched with two control singleton pregnancies for gestational age (same completed week) and duration of sample storage (same calendar quarter). The median free alpha-hCG level in the IDDM pregnancies was 0.86 multiples of the median (MOM) for pregnancies without IDDM at the same gestational age (P < 0.002) (95 per cent confidence interval 0.80-0.94). The corresponding free beta-hCG level was 0.96 MOM (95 per cent confidence interval 0.85-1.09). These results enable free alpha-hCG values to be adjusted so that antenatal screening for Down's syndrome can be performed using this marker in IDDM pregnancies as well as in non-diabetic pregnancies.

Characteristics of CD4+ T cells which transfer murine AIDS (MAIDS)

The murine acquired immunodeficiency syndrome (MAIDS) is caused in susceptible C57BL/6 (B6) mice by a defective murine leukemia virus (MuLV) and resembles human AIDS in several respects. The disease is characterized by hypergammaglobulinemia, polyclonal B cell activation, lymphadenopathy, and generalized immunosuppression within 5-8 weeks postinfection. The virus has been shown to infect B cells and macrophages and both T and B cells are required for MAIDS development. The manner in which T cells contribute to the disease process is not known. We report here that this retroviral infection leads to induction of a Thy-CD4+T cell subpopulation capable of transferring all the symptoms of MAIDS disease to normal B6 and B6 nu/nu. Essentially 100% of T cells recovered from B6 nu/nu mice, injected with CD4+ T cells from B6 MAIDS animal, is of the Thy-CD4+ phenotype. The proliferation of these T cells in culture and their ability to cause MAIDS in SCID mice is totally dependent on the presence of B cells. These T cells do not exhibit significant V beta restriction of their T cell receptors (TCR) and, by PCR analysis, have defective virus-specific sequences in the cellular genome. By several criteria, however, these cells do not produce the infectious virus. These results suggest that a B-cell-dependent population of CD4+ T cells from MAIDS animals, in the absence of detectable infectious virus production, has the ability to transfer MAIDS-like disease.

Dose-dependent carcinogenicity and frequent Ki-ras proto-oncogene activation by dietary N-nitrosodiethylamine in rainbow trout

While the experimental data upon which current concepts in mechanistically based risk assessment and molecular epidemiology are grounded derive almost entirely from rodent models, fish models have several attributes (e.g., low background incidence, extremely low cost tumor studies, nonmammalian comparative status for extrapolation of mechanisms to humans) that make them valuable adjuncts for addressing these concepts. This report provides an initial characterization of the dose dependency of dietary N-nitrosodiethylamine (DEN) hepatocarcinogenicity in Shasta strain rainbow trout (Oncorhynchus mykiss) and the potential of DEN to elicit ras proto-oncogene activation in this species. Carcinogen was administered in the diet at five concentrations for 12 months. Necropsies were performed at 9, 12, and 18 months, the latter on fish maintained on control diet for 6 months after cessation of DEN exposure. The incidence of hepatic neoplasms at the lower dietary concentrations (< or = 70 ppm) did not consistently exceed that for control groups, which were higher in this particular study (2%) than expected (historically 0.1%). For the higher DEN concentrations, a linear relationship between the hepatic tumor incidence (expressed as log odds, log [p/(1-p)], where p = proportion of fish bearing tumors), and the logarithm of total cumulative dose was observed, with response being independent of the length of time (9 or 12 months) during which the dose was accumulated. The dose-response curve for fish maintained an additional 6 months postexposure was shifted toward higher incidence but was parallel to the curve for fish killed at cessation of exposure. The model predicts that doubling the dose will produce somewhat more than a doubling of the odds (p/(100-p)) for tumor incidence and that the odds for lesions 6 months postexposure will be approximately double those at cessation of exposure. Comparison of these results with previous studies using rats suggests an overall similarity in dose-response curves, with trout being somewhat less sensitive than rats to DEN hepatocarcinogenesis. To examine the molecular basis for DEN carcinogenesis in this species, seven liver tumors induced separately by short-term DEN treatment were probed by 3'-mismatch primer polymerase chain reaction analysis for evidence of Ki-ras proto-oncogene activating point mutations. A very high proportion (6/7) of tumors was found to carry codon 12 GGA-->AGA mutations, whereas no codon 61 mutants were detected in this sample.(ABSTRACT TRUNCATED AT 400 WORDS)

Cloning, characterization, and distribution of a mu-opioid receptor in rat brain

We report the isolation and characterization of a rat cDNA clone encoding a mu-opioid receptor. This receptor, a 398 amino acid protein, shares 59% overall identity with the mouse delta- and kappa-opioid receptors. Transient expression of the receptor in COS cells revealed high-affinity binding of mu-selective opioid antagonists and agonists, with a KD for naloxone approximately 1.5 nM, and for [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) and morphine at the high-affinity site of 2-4 nM, confirming a mu-opioid pharmacological profile. Northern blotting and in situ hybridization histochemistry revealed that the mu-opioid receptor mRNA was expressed in many brain regions, including cerebral cortex, caudate putamen, nucleus accumbens, olfactory tubercle, septal nuclei, thalamus, hippocampus, and medial habenular nucleus, in keeping with the known distribution of the mu-opioid receptor.

Arbitrarily primed PCR fingerprints resolved on SSCP gels

Images

Biodistribution and preclinical radioimmunotherapy studies using radiolanthanide-labeled immunoconjugates

Lutetium-177 (177Lu), samarium-153 (153Sm), and yttrium-90 (90Y) are members of the family of elements known as lanthanides or rare earths. Monoclonal antibody CC49, a murine immunoglobulin (Ig) G1, which is reactive with the tumor-associated antigen TAG-72, previously has been shown to react with a wide range of human carcinomas. The authors review here the comparative biodistributions of CC49 IgG and F(ab')2 fragments labeled with 177Lu, 153Sm, and 90Y using the bifunctional chelating agent PA-DOTA. The authors also review the results of a biodistribution study comparing iodine-125-labeled and 177Lu-labeled CC49 sFv, and the use of 177Lu-CC+9 IgG in an experimental therapy model. Chelation and conjugations gave similar yields, and the labeled proteins showed similar retention of immunoreactivity regardless of the isotope used for both IgG and F(ab')2. Biodistribution data obtained in athymic mice bearing LS-174T human colon carcinoma xenografts likewise showed no differences among the three radioisotopes for both IgG and F(ab')2. Femur uptake of radioactivity was lower than previously reported for other radiolanthanide immunoconjugates. Different metabolic patterns were observed for radioiodinated versus radiometal-labeled sFv, particularly in the kidney, where localization of the latter was increased dramatically. 177Lu-CC49 was found to delay the growth of established LS-174T human colon carcinomas in athymic mice at a single dose of 50 microCi. Elimination of established tumors was demonstrated over the observation period (77 days) using single administrations of 200 or 350 microCi. Dose fractionation experiments revealed that the mice tolerated 750 microCi (3 x 250 microCi, given weekly), whereas > 50% of the mice died after receiving a single administration of approximately 500 microCi. In isotype-matched control experiments, a large differential in the therapeutic effects was observed between 177Lu-labeled control antibody and CC49.

Polymorphisms of the D4 dopamine receptor alleles in chronic alcoholism

We have screened genomic DNA for the identification of D4 dopamine receptor polymorphisms. We show that the D4 dopamine receptor genotype in 72 severely affected chronic alcoholics is heterogeneous, with individuals homozygous and heterozygous for the various D4 receptor alleles. Alcoholics demonstrated a greater prevalence of the D4(3) (p < 0.005) and D4(6) (p < 0.005) alleles than has been reported in normals. There was a high prevalence of nicotine abuse among all D4 genotypes. The frequency of other drug abuse was higher in the D4(3,3) and the D4(4,7) groups, and the family history was strongly positive in the D4(2,4) group. The distribution of the D2 alleles showed equivalence in all D4 genotypes, except in D4(4,6) and D4(4,7) in whom the prevalence of the D2 A1A2 allele was 2-fold higher. The polymorphic variations of the D4 receptor genes should be among the factors considered in the assessment of individual differences in susceptibility to disorders such as alcohol abuse or drug addiction that may be mediated through central dopaminergic systems.

mei-3, a recombination and repair gene of Neurospora crassa, encodes a RecA-like protein

Neurospora crassa mei-3 is a mutant which exhibits meiotic and mitotic defects and mutagen sensitivity. Its defect is believed to be in recombination and repair. We have cloned the mei-3 gene from a N. crassa cosmid library of genomic DNA. Restriction fragment length polymorphism analysis determined the location of the cloned fragment was on chromosome one in approximately the same position that was previously reported for mei-3 by classical genetic methods. Deletion analysis showed the approximate coding region of mei-3 on the cloned genomic fragment. Northern blot analysis identified a 900-bp transcript. Sequencing revealed a 798-bp open reading frame with high coding preference which could encode a protein having a molecular weight of approximately 29,000. The predicted protein product of mei-3 has significant identity to the Rad51 and Dmc1 proteins from Saccharomyces cerevisiae. The mei-3 gene and both yeast genes have significant primary sequence homology with RecA, a recombination protein identified in Escherichia coli. The results suggest RecA-like proteins involved in DNA recombination and repair are highly conserved in eukaryotes.

The use of free beta-hCG in antenatal screening for Down's syndrome

OBJECTIVE

To investigate the value of the measurement of free beta human chorionic gonadotrophin (hCG) as a serum marker of Down's syndrome in the second trimester of pregnancy.

DESIGN

A prospective observational study using stored antenatal serum samples.

SETTING

Serum samples collected from women receiving routine antenatal care in Oxford.

SUBJECTS

Seventy-five singleton pregnancies with fetal Down's syndrome and 367 unaffected singleton pregnancies. Each affected pregnancy was matched with five control pregnancies for maternal age, gestational age, and duration of storage of the serum sample. None of the pregnancies were associated with neural tube defects.

MAIN STUDY MEASURES

Maternal serum free beta-hCG levels. These were compared with total hCG levels in the same pregnancies. The performance of screening using free beta-hCG was compared with that using the principal markers, namely alpha-fetoprotein (AFP), unconjugated oestriol (uE3), and total hCG together with maternal age.

RESULTS

The median free beta-hCG level in the affected pregnancies was 2.22 multiples of the normal median (MoM), significantly higher than in the unaffected pregnancies (95% confidence interval, 1.84-2.68 MoM). The discriminatory performances of free beta-hCG and total hCG, each considered separately, were similar; with a cut-off level of 2.5 MoM the detection rate was 43% and 5.7 of unaffected pregnancies had raised free beta-hCG levels (likelihood ratio of 7.5 (43/5.7)), somewhat better discrimination than the 32% and 4.6% respectively using total hCG (likelihood ratio of 7.0 (32/4.6)). With a higher cut-off level of 3.5 MoM, the rates were 19% and 2.7% respectively (likelihood ratio of 7.0), using free beta-hCG, worse than the 19% and 1.4% using total hCG (likelihood ratio of 13.6). Screening using maternal age, AFP, uE3 and free beta-hCG (instead of total hCG) yielded a detection rate of 62% (instead of 58%) at a screening risk cut-off level corresponding to a 5% false-positive rated).

CONCLUSION

The main advantage in using free beta-hCG instead of total hCG is that there is a small increase in the detection rate (4%) for a given false-positive rate when used with maternal age, AFP and uE3. The main disadvantage is that there is less practical experience with free beta-hCG measurement and insufficient data to screen in certain categories of pregnancy (e.g. twins). The best practical advice is to use total hCG for the present but consider changing to free beta-hCG either (i) after further data are available that will permit the interpretation of screening results in the same way as is currently available with total hCG, or (ii) if its use with another marker confers a worthwhile increase in the detection rate for a given false-positive rate.

Carcinogenicity, metabolism and Ki-ras proto-oncogene activation by 7,12-dimethylbenz[a]anthracene in rainbow trout embryos

Field studies suggest that recent epizootics of hepatic neoplasms in some feral fish populations are associated with polycyclic aromatic hydrocarbon (PAH) exposure, but attempts to induce liver tumors in these species under laboratory conditions have been unsuccessful. Several studies have shown hepatic neoplasma to be inducible in laboratory fish species following PAH exposure at the free-swimming life stage. However, neither the susceptibility of the fish embryonic life stage to tumor induction by PAHs nor the potential of these carcinogens to induce oncogenic point mutations analogous to those reported in feral fish hepatic tumors have been clearly established. To address this, rainbow trout embryos were exposed by passive water uptake to 7,12-dimethylbenz[a]anthracene (DMBA), a potent model PAH in many mammalian tumor protocols. DMBA was rapidly absorbed by trout eggs and metabolized. The major non-polar metabolites identified were 12-hydroxymethyl-7-methylbenz[a]anthracene and 3,4-dihydroxy-3,4-dihydro-DMBA, whereas approximately 25% of the water soluble metabolites were identified as glucuronides by beta-glucuronidase treatment. Embryonic DNA adduction increased with time of DMBA exposure (2.2 +/- 0.3 pmol DMBA-equivalents/mg DNA at 24 h). Liver tumor incidence nine months after DMBA treatment was found to increase with DMBA concentration and exposure period (3.8% at 1 p.p.m./2 h; 23% at 5 p.p.m./2 h; 85% at 5 p.p.m./24 h). Stomach adenomas and nephroblastomas also were observed at low incidence in the DMBA-treated trout. Among 11 hepatic tumors examined, nine carried Ki-ras alleles with activating point mutations in codon 12 (4/11 GGA-->AGA; 4/11 GGA-->GTA) or codon 61 (1/11 CAG-->CTG). This spectrum differs substantially from those reported for DMBA-initiated mouse skin papillomas or hepatic tumors. These results may have important environmental implications because they suggest that even a brief exposure to PAHs during a sensitive stage of development may adversely affect some fish populations. They also indicate considerable variation in DMBA ras gene mutations among species and target organs.