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The aim of this paper is to report the views of academic dentists about careers in academic dentistry assessed by method of a postal questionnaire survey. The subjects of the survey were dentists in academic posts in the United Kingdom. The incentives in pursuing an academic career which respondents rated most highly were the opportunity to teach and the variety of work in an academic career. The greatest disincentives were competing pressures from service work, teaching and research, and the difficulty of getting research grants. Many would like to spend more time on research and less on service work and teaching. The length of time required for training, and the quality of training, was a concern, particularly for junior academics. Most respondents rated the enjoyment of their job highly but scored much lower on satisfaction with the time their job left for domestic and leisure activities. By contrast with academic medicine, in academic dentistry there is typically greater emphasis on teaching and less on research. In conclusion, the balance of activities in academic posts, particularly between service work, teaching and research, needs to be regularly reviewed. The development of a more structured training programme for junior academics, which does not disadvantage academic dentists when compared with their NHS colleagues, may be required.

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OBJECTIVE: To investigate junior doctors' views about careers in academic medicine. DESIGN: Postal questionnaire survey. SETTING: National Health Service in England. SUBJECTS: Doctors in university posts at specialist registrar level, Medical Research Council and Wellcome Trust training fellows, and specialist registrars in National Health Service posts. RESULTS: Incentives to pursue an academic career which respondents rated as strong related to the challenge of research and the intellectual environment of research units. The strongest disincentives were perceived difficulties in obtaining research grants and uncertainty regarding pay parity with National Health Service colleagues. Medical Research Council and Wellcome fellows had much more protected research time than other academic doctors but were less satisfied with their clinical training. Academic doctors who were not fellows reported spending less than half their time on research and the great majority agreed that their research suffers when there is pressure on the service side. CONCLUSIONS: The job content of academic posts should be kept under regular review to ensure that clinical service pressures do not inappropriately erode research time while also ensuring that postholders have adequate clinical training. Training programmes need flexibility to accommodate the needs of clinical academics in their progress through higher specialist training.

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The behaviour in vivo of tight and loose variants of murine melanoma cells is further characterized. In vitro clonal morphology is reproduced on a variety of substrates. Results suggest that repeated selection of loose cells can co-select for cells with high metastatic and colonization potentials. Measurement of cell motility shows that 1G3 (loose) cells are more motile than 1G8 (tight) which are restricted to movements within clonal boundaries. Studies of adhesive properties show that loose cells are more easily detached from the substrate with trypsin or EDTA and that both cell lines attach more quickly to monolayers of loose cells than to tight ones. No gross differences are found either in attachment rates to plastic and ECM or in aggregation and disaggregation rates. Analysis of the cell surface has not revealed any differences between 1G8 and 1G3 in the sialylation of terminal galactose and N-acetylgalactosamine residues or in neuraminidase releasable sialic acid. The binding patterns of iodinated lectins to SDS-PAGE separated proteins are similar for both lines except for one 85/90 KD protein which is more abundant in 1G3 than 1G8 cells after neuraminidase treatment. The results show enhanced differences in metastatic potential of tight and loose clones after selective cloning and that there may be important differences in motility and cell-substrate interactions.

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A monoclonal antibody, GTE52, was isolated from a fusion of myeloma cells with the lymphocytes of a mouse immunised with enzymatically dissociated guinea-pig trigeminal ganglion cells. GTE52 was found to stain the nuclei of satellite cells and Schwann cells, but not neurones, in the peripheral nervous system of guinea-pig and mouse. In the central nervous system GTE52 labelled glia and some neurones. Double-labelling experiments on primary cultures of optic nerve using antibodies to glial fibrillary acidic protein, galactocerebroside and fibronectin showed that GTE52 labelled a sub-population of astrocyte glia, possibly corresponding to the type 2 astrocytes, oligodendrocytes and not fibroblasts. Adult non-neural tissue was not stained by GTE52 with the exception of the smooth muscle of the gut. However, during development of the guinea-pig the antigen recognised by GTE52 was expressed in all cells of 16-day embryos but was lost from the tissues studied, which were not stained in the adult, from about embryonic day 60 onwards.

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The catecholaminergic neurons of the nervous system have been studied histochemically with fluorescent derivatives of catecholamines and immunocytochemically using antibodies against their biosynthetic enzymes. The immunocytochemical techniques yield permanent preparations and make possible ultrastructural studies and combined applications with other procedures. In this report, we describe the production and application of a high-affinity mouse monoclonal antibody against the rate-limiting enzyme in the biosynthetic pathway of the catecholamines, tyrosine hydroxylase. This antibody, coded TOHA1.1, has been used successfully to stain tyrosine hydroxylase immunoreactive sites in the known catecholaminergic neurons and fiber systems of rat brain in both light and electron microscopy. It has also been demonstrated that TOH A1.1 will immunoprecipitate phosphorylated tyrosine hydroxylase.

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Mouse antibodies are increasingly used as primary antibodies for immunocytochemistry as more mouse monoclonal antibodies are being produced. The localisation of these antibodies by the PAP technique requires mouse antiperoxidase antibody. A monoclonal antiperoxidase would obviate the limitations of production of a polyclonal mouse antiperoxidase. This paper describes the development of a mouse hybridoma producing such an antibody (MAP A6-2) and the use of this antibody to localise a number of mouse primary antibodies by the PAP technique for both light and electron microscopy. The antibodies localised include monoclonal antienkephalin and antityrosine hydroxylase. MAP A6-2 had a higher affinity in immuno-diffusion experiments and gives slightly better staining with an horse radish peroxidase of a different type from that used for immunisation. Staining was optimum with horse radish peroxidase type X whereas horse radish peroxidase type VI was used for immunisation. Also described is the production of a HAT sensitive variant cell line allowing the possibility of using this hybridoma as a parent cell line for the production of hybrid hybridomas secreting bi-specific antibodies.

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The development of two monoclonal antibodies for use as second antibodies in immunocytochemistry is described. The antibodies are produced by mouse X mouse hybrid myelomas, and are both of the IgG type. The two antibodies, RB23 and ND13, were used to detect neurophysin by three-step peroxidase-antiperoxidase (PAP) immunostaining, and were "internally labeled" with 3H-lysine for the radioimmunocytochemical localization of neurophysin, substance P, and tyrosine hydroxylase using rabbit first antibodies. The binding sites of RB23 and ND13 on the rabbit IgG antibodies were determined by solid-phase radioimmunoassay, using allotype-specific rabbit serum to compete with RB23 and ND13. It was found that both RB23 and ND13 are directed against the B4 kappa-light-chain allotype. The immunocytochemical localization of adrenocorticotropic hormone and somatostatin with rabbit primary antibodies was not achieved with RB23 or ND13, and it is proposed that these antibodies are not of the B4 allotype. The findings demonstrate that monoclonal second antibodies can be useful general reagents for conventional immunocytochemistry as well as for radioimmunocytochemistry. Furthermore, allotype-specific monoclonal second antibodies may prove useful in the simultaneous immunohistochemical localization of more than one antigen in a given tissue section.

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The highly metastatic mouse melanoma cell line F87 C16 T2 is heterogeneous for clonal morphology in vitro. Tight, intermediate and loose morphologies can be distinguished. The tight and loose morphologies are selectable on repeated subcloning and stable for at least 15 passages in vitro. Both types of clones and the cell lines derived from them produce tumours in mice but the loose cells produce faster growing primaries and more secondary deposits than tight cells. The loose cells grow only marginally faster than the tight cells in vitro and the saturation densities of both are similar. Direct cloning of cells dissociated from tumours shows that the tight and loose morphologies are stable in vivo and that there is no obvious selection for either cell type in primary or secondary tumours. Nevertheless injections of progressively fewer cells suggests that loose cells are up to ten times more efficient at producing tumours. Our findings are discussed in relation to current ideas on the importance of heterogeneity and selection in the production of metastases.

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Cell fusion has been used to analyse the genetic determinants of metastasis at the cellular level. Highly metastatic mouse melanoma cells were fused with diploid mouse lymphocytes and a range of hybrid clones isolated and tested for tumorigenicity and metastatic potential by s.c. injection into newborn, histocompatible, sublethally-irradiated mice. Although almost all clones tested were tumorigenic, most had considerably reduced metastatic potential. This suggests that tumorigenicity and metastasis are determined by different genetic elements. Histological examination of primary tumours produced by metastatic and non-metastatic hybrid cell lines showed that an essential step in the production of metastases is the separation of tumour cells from the main tumour mass and their movement into the surrounding tissues. The primary tumours of a metastatic hybrid cell line showed local invasiveness whereas those of a non-metastatic cell line did not.

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The ability of cultured tumor cell lines to invade across epithelia was studied by placing 10(4) to 10(6) dispersed cells on the chorionic epithelium (CE) of the chorioallantoic membrane of the 10-day chick embryo. Tumor lines included Walker carcinosarcoma, F87 cl 6T2 and B16-BL6 melanomas, and KiSV-NIH, 3B77SC4, and HT 1080 sarcomas. The CE is a bilayer of cells with a superficial periderm overlying a basal layer. Invasion across an intact CE was very weak (limited to the formation of "microtumors" by a small fraction of the inoculated cells in 5 to 50% of the embryos) but was massive (most or all of the inoculated cells invaded in over 99% of the embryos) if the chorioallantoic membrane was traumatized in a fashion which disrupted the periderm but left the basal layer intact. Normal fibroblasts also invaded across the traumatized CE. The histological picture of invasion suggests that cells inoculated on the traumatized CE induced large-scale active retraction of the basal layer, resulting in the formation of large gaps in its continuity. Migration into the subjacent mesoderm occurred through these gaps. The nodules formed by both tumorigenic and normal cells became extensively vascularized within 3 days.

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Immunofluorescence studies showed that most binucleate Vero cells formed by virus-induced fusion or by inhibition of cytokinesis had a single microtubule-organizing centre (MTOC) when examined during the reassembly of microtubules after chilling, but two or more organizing centres when examined after exposure to colcemid. These findings suggest that although binucleate cells initially contain more MTOC than mononucleate cells, the extra MTOC are normally aggregated, so that the number of MTOC in binucleate cells tends to be reduced very quickly to that in mononucleate cells.

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The lecture reviews some aspects of the work on the analysis of malignancy that have been, and are now being, pursured in the Dunn School. A brief outline of the early experiments that first demonstrated that the malignancy of mouse tumor cells can be suppressed by the fusion with normal cells is given, and then two areas of current interest in the laboratory are described. The first is an attempt to analyze the clinically important property of tumors to metastasize and the second is the work on the isolation and identification of an abnormal membrane glycoprotein present in tumor cells. In addition the value of cell fusion methods as a general test of hypotheses of malignancy is emphasized.

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