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An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

RESUMEN

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

RESUMEN

Body-axis elongation constitutes a key step in animal development, laying out the final form of the entire animal. It relies on the interplay between intrinsic forces generated by molecular motors1-3, extrinsic forces exerted by adjacent cells4-7 and mechanical resistance forces due to tissue elasticity or friction8-10. Understanding how mechanical forces influence morphogenesis at the cellular and molecular level remains a challenge1. Recent work has outlined how small incremental steps power cell-autonomous epithelial shape changes1-3, which suggests the existence of specific mechanisms that stabilize cell shapes and counteract cell elasticity. Beyond the twofold stage, embryonic elongation in Caenorhabditis elegans is dependent on both muscle activity7 and the epidermis; the tension generated by muscle activity triggers a mechanotransduction pathway in the epidermis that promotes axis elongation7. Here we identify a network that stabilizes cell shapes in C. elegans embryos at a stage that involves non-autonomous mechanical interactions between epithelia and contractile cells. We searched for factors genetically or molecularly interacting with the p21-activating kinase homologue PAK-1 and acting in this pathway, thereby identifying the α-spectrin SPC-1. Combined absence of PAK-1 and SPC-1 induced complete axis retraction, owing to defective epidermal actin stress fibre. Modelling predicts that a mechanical viscoplastic deformation process can account for embryo shape stabilization. Molecular analysis suggests that the cellular basis for viscoplasticity originates from progressive shortening of epidermal microfilaments that are induced by muscle contractions relayed by actin-severing proteins and from formin homology 2 domain-containing protein 1 (FHOD-1) formin bundling. Our work thus identifies an essential molecular lock acting in a developmental ratchet-like process.

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A distinctive feature of polarized epithelial cells is their specialized junctions, which contribute to cell integrity and provide platforms to orchestrate cell shape changes. This chapter discusses the composition, assembly and remodeling of C. elegans cell-cell (CeAJ) and hemidesmosome-like cell-extracellular matrix junctions (CeHD), proteins that anchor the cytoskeleton, and mechanisms involved in establishing epithelial polarity. Major recent progress in this area has come from the analysis of mechanisms that maintain cell polarity, which involve lipids and trafficking, and on the impact of mechanical forces on junction remodeling. This chapter focuses on cellular, rather than developmental, aspects of epithelial cells.

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Caenorhabditis elegans has been introduced relatively late into the field of autophagy with no previous results by classical methods. Therefore, it has to be studied in parallel with both traditional electron microscopy and modern molecular approaches. In general, correct identification of autophagic elements by electron microscopy is indispensable to establish a firm basis for our understanding of the process. The principles and the method for identification, applied also for C. elegans, are summarized first in this article, to facilitate their utilization both for further studies and the analysis of new cell types and to support researchers new to electron microscopy techniques. Studying autophagy in the worm by electron microscopy has required the development of special handling and sampling techniques in addition to overcoming the general technical difficulties due to the nature of C. elegans samples. These are described in detail, together with some initial qualitative and quantitative results obtained by them. The feasibility of the presented method is supported by data which show that in continuously fed worms the autophagic compartment is in the lower range of the 10(-2)% order of magnitude of the cytoplasmic volume, while immediately after molting or upon starvation in the second larval period, usually more than a 10-fold increase can be measured. In dauer larvae, individual variation of the autophagic compartment is very high. The predauer stage in daf-2 mutants does not seem to show significant constitutive autophagic activity. Some autophagy-related gene mutants show characteristic ultrastuctural features, such as autophagosomes with membrane abnormalities (unc-51/Atg1) or the hypertrophy of multivesicular bodies (let-512/Vps34, bec-1/Atg6).

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Autophagy (cellular self-eating) is a highly regulated, lysosome-mediated catabolic process of eukaryotic cells to segregate by a special membrane and subsequently degrade their own constituents during development or starvation. Electron microscopy analysis reveals autophagic elements in various cell types of the nematode Caenorhabditis elegans, whose genome contains counterparts of several yeast genes involved in autophagy. Genetic manipulation inactivating autophagy-related genes in C. elegans causes defects in development, affects dauer larval morphogenesis, accelerates aging thereby shortening life span, reduces cell size, decreases survival during starvation, promotes apoptotic cell death, and protects neurons from undergoing hyperactive ion channel- or neurotoxin-induced degeneration. These results implicate autophagy in various developmental and cellular functions such as reproductive growth, aging, and cell growth, as well as cell survival and loss. This chapter discusses methods of inactivating C. elegans autophagy genes by RNA interference, testing the resistance of autophagy-deficient nematodes to starvation-induced stress, handling mutants carrying a deletion in the autophagy pathway, and monitoring autophagic activity by using LysoTracker Red dye or reporters labeled with green fluorescent protein. Such methods may be adaptable to identify additional roles of autophagy in development and cellular function, and may also help to detect the intracellular accumulation of autophagy proteins and monitor autophagosome formation.

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Tenascin, an extracellular matrix glycoprotein, is widely expressed in the stroma of almost all types of solid tumours including malignant melanomas. On the basis of its antiadhesive character, it has been supposed that tenascin accumulation facilitates tumour cell invasion and consequent metastasis formation. We aimed to investigate the mechanism by which melanoma cells can modulate the production of tenascin by host stromal cells. The expression of tenascin in cocultures of fibroblasts and five melanoma cell lines, as well as in fibroblast monocultures treated with melanoma conditioned media, was analysed by immunofluorescent staining and image analysis. Tenascin production could not be observed in control fibroblasts or in melanoma cell monocultures. Faint labelling for tenascin could be detected in fibroblast monocultures treated with melanoma cell conditioned media while a very intense staining for tenascin could be seen in melanoma cell-fibroblast cocultures. The tenascin staining in the cocultures was associated with the fibroblasts that were in close contact with melanoma cells. The level of tenascin production around the fibroblasts in different areas of the cocultures correlated well with the density of melanoma cells. Our results indicate that tenascin production of fibroblasts in the tumour stroma is directly modulated by melanoma cells mainly through cell-to-cell contact signalling.

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BACKGROUND: The relationship between socioeconomic status and preventive care is an important issue in public health practice in Hungary. Our aim was to investigate the association between the socioeconomic status and the present practice of primary allergy prevention in infant feeding in Hajdú-Bihar County, Hungary. METHODS: A questionnaire-based cross-sectional survey was performed among 3076 infants aged 0-6 months. We studied how socioeconomic status, type of settlement, allergic background of the family and skin symptoms indicative for allergy were related to primary allergy prevention in infant feeding. Prevalence odds ratios (ORs) were calculated by multiple logistic regression. RESULTS: Independent determinants of breast feeding were age [OR corresponding to one month change 0.74; 95% confidence interval (CI) 0.70-0.77], the female gender (OR 1.24; 95% CI 1.06-1.46), the socioeconomic status of the family (OR comparing the worst with the best category 0.63; 95% CI 0.43-0.93), and birth weight (OR comparing <1500 g to >2500 g category 0.17; 95% CI 0.07-0.41). Among supplementary nutrient users independent determinants of the use of hydrolysed infant formulae were the socioeconomic status (OR comparing the worst with the best category 0.06; 95% CI 0.01-0.27), the type of settlement (OR comparing village with town 0.48; 95% CI 0.28-0.80), history of allergy in the family (OR 2.30; 95% CI 1.28-4.11), and skin symptoms indicative of allergy (OR 3.46; 95% CI 1.96-6.14). CONCLUSION: Socioeconomic status is related to the implementation of primary allergy prevention in infant feeding.

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BACKGROUND: In 1998 a joint initiative of the Hungarian School of Public Health and the National Public Health Service created a network of sentinel stations based in primary care facilities in four Hungarian counties. The aim was to establish a system that will provide valid data on morbidity of selected diseases in Hungary. METHODS: Based on standardized protocols, the participating centres have continuously reported data on the prevalence of cardiovascular diseases, diabetes mellitus, liver cirrhosis, and some malignant diseases, as well as supplying denominator data. The four counties represent both eastern and western parts of Hungary, reflecting the known geographical disparities in health. Each county office enrolled general practitioners maintaining representation in terms of both geography and distribution of settlement size. RESULTS: A total of 73 general practitioners agreed to participate, providing care for 15.6% (138,088 people) of the population in the counties. The population registered with the practices were representative in terms of age and sex of both the participating counties and the entire country. The prevalence of hypertension, diabetes mellitus and liver cirrhosis is high in each county but varies considerably, with higher levels in the western counties, especially among older age groups of both sexes. CONCLUSIONS: The establishment of sentinel stations to collect morbidity data is feasible and sustainable in Hungarian primary care. The data that have been generated provide a valid and comprehensive picture of important aspects of the Hungarian population's health, with important implications for health policy and health service planning. In regions where low prevalence rates of diseases and high mortality rates simultaneously exist special attention is required to explore the background of this caveat. KEY POINTS: Till the end of 1998 no program operated in Hungary engaged with non-communicable disease morbidity data collection, except some hospital-based registries, which failed to produce reliable information. The establishment of sentinel stations to collect morbidity data is feasible and sustainable in Hungarian primary care, the valid morbidity data can be built into the decision making process in health service planning. Regular training, quality control and feedback are important contributors to the success of the program. The prevalence of hypertension, diabetes mellitus and liver cirrhosis is high in each county but varies considerably, with higher levels in the western counties, especially among older age groups of both sexes. More research needed to determine the possible contribution of unknown morbidity and health service utilisation to the different prevalence values in the two parts of Hungary.

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