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Periostin-like factor (PLF) and Periostin are alternatively spliced mRNAs. Our findings are the first to show similarities and differences between PLF and Periostin location using isoform-specific antibodies. The differences in when and where they are present during mouse embryogenesis suggest that they may have different functions. Using immunostaining techniques, we observed that PLF was highly expressed at 12.5 days postconception (dpc) in the intermediate and outer zones of most brain regions, spinal cord, cranial and spinal nerves, and chondrocytes in developing bone and in the heart wall. By 16.5 dpc, PLF was also present in ameloblasts and odontoblasts in developing teeth, and by 19.5 dpc, PLF was present at low levels only in vagal nerve bundles, discrete white matter bundles in the brain, and chondrocytes of developing ribs. Periostin, on the other hand, was absent at 12.5 dpc from dorsal spinal cord and from cranial and spinal nerves. By 16.5 dpc, Periostin was present in many spinal nerves, but absent thereafter, and at 19.5 dpc, Periostin was present in chondrocytes in developing bone but not in neural tissues. The different spatial and temporal location of PLF and Periostin in cartilage and bone cells suggests different roles for these proteins in endochondral bone formation. The early expression of PLF in brain differentiation zones and in developing axon bundles and nerves suggests that it may facilitate axon growth. (J Histochem Cytochem 56:329–345, 2008)

The Receptor for Advanced Glycation Endproducts [RAGE] is an evolutionarily recent member of the immunoglobulin super-family, encoded in the Class III region of the major histocompatability complex. RAGE is highly expressed only in the lung at readily measurable levels but increases quickly at sites of inflammation, largely on inflammatory and epithelial cells. It is found either as a membrane-bound or soluble protein that is markedly upregulated by stress in epithelial cells, thereby regulating their metabolism and enhancing their central barrier functionality. Activation and upregulation of RAGE by its ligands leads to enhanced survival. Perpetual signaling through RAGE-induced survival pathways in the setting of limited nutrients or oxygenation results in enhanced autophagy, diminished apoptosis, and (with ATP depletion) necrosis. This results in chronic inflammation and in many instances is the setting in which epithelial malignancies arise. RAGE and its isoforms sit in a pivotal role, regulating metabolism, inflammation, and epithelial survival in the setting of stress. Understanding the molecular structure and function of it and its ligands in the setting of inflammation is critically important in understanding the role of this receptor in tumor biology.