Microarray hybridization has rapidly evolved as an important tool for genomic studies and studies of gene regulation at the transcriptome level. Expression profiles from homogenous samples such as yeast and mammalian cell cultures are currently extending our understanding of biology, whereas analyses of multicellular organisms are more difficult because of tissue complexity. The combination of laser microdissection, RNA amplification, and microarray hybridization has the potential to provide expression profiles from selected populations of cells in vivo. In this article, we present and evaluate an experimental procedure for global gene expression analysis of slender embryonic structures using laser microbeam microdissection and laser pressure catapulting. As a proof of principle, expression profiles from 1000 cells in the mouse embryonic (E9.5) dorsal aorta were generated and compared with profiles for captured mesenchymal cells located one cell diameter further away from the aortic lumen. A number of genes were overexpressed in the aorta, including 11 previously known markers for blood vessels. Among the blood vessel markers were endoglin, tie-2, PDGFB, and integrin-1, that are important regulators of blood vessel formation. This demonstrates that microarray analysis of laser microbeam micro-dissected cells is sufficiently sensitive for identifying genes with regulative functions.
The clinical and experimental use of infrared scanning instruments for surface temperature measurements requires a knowledge of heat distribution in living tissue. A heat coil and a temperature registering thermistor encased in titanium were implanted subcutaneously in rabbits. After a healing period the relation between the power output from the heat sources at various depths and the temperature pattern of the overlying skin surface was studied.
The medical application of infrared thermography makes use of the skin temperature as an indication of an underlying pathological process. In order to study the relation between the heat production from a source in living tissue and the overlying skin temperature, artificial heat sources were implanted subcutaneously in human volunteers. The experimental results show that a detectable surface temperature increase over the heat sources presupposes high power output or superficial implantation. The effect of forced convective heat loss from the skin surface and lowered ambient temperature was studied. Forced convection markedly decreased the temperature contrast. An implicit conclusion from experimental and theoretical work is that a localized 'hot spot' can only exceptionally be attributed to metabolic heat production conducted to the skin surface from a buried pathological process. The thermal pattern over a breast tumour, a septic or aseptic inflammation or a tissue injury mainly reflects the vascular reaction.
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