Browsing by Author "Dr. Betty L. Black, Committee Co-Chair"

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    Embryonic Epithelial Development is Modulated by Extracellular Calcium
    (2002-09-23) Mack, Cina Marie; Dr. Betty L. Black, Committee Co-Chair; Dr. Russell Borski, Committee Co-Chair; Dr. Robert Argenzio, Committee Member; Dr. Herbert Underwood, Committee Member
    This study investigated the effects of calcium on epithelial differentiation in organ-cultured embryonic chick duodenum. Alteration of calcium ion concentration of culture medium above or below the physiological Ca2+ concentration of embryonic chick serum strongly influenced gastrointestinal development. Culture of 16- or 18-day embryonic intestine in high Ca2+ resulted in elevated activity of alkaline phosphatase, a brush border digestive enzyme, and an increase in goblet cell number within the epithelium. Conversely, low Ca2+ reduced both indices of functional differentiation. Lead acetate, a disruptor of Ca2+ homeostasis, was as effective as low Ca2+ in impeding epithelial differentiation. The voltage sensitive Ca2+-channel (VSCC) antagonists verapamil and nifedipine were used to selectively block Ca2+ influx into the cultured tissue. Both verapamil, a non-specific channel blocker, and nifedipine, which is highly selective for L-type VSCCs, significantly inhibited differentiation, but nifedipine gave more consistent results. Imaging of calcium within the epithelium of cultures was performed by confocal scanning laser microscopy, using the fluorescent calcium probe indo-1. Quantification of Ca2+ within enterocytes revealed that both verapamil and nifedipine reduced intracellular Ca2+ concentration. Together, these results indicate that extracellular Ca2+ influences epithelial differentiation by modulating intracellular Ca2+-dependent signaling pathways, possibly mediated by VSCCs.
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    Expression of Claudin Tight Junction Proteins in Response to Varying Environmental and Physiological Conditions.
    (2009-01-05) Ozden, Ozkan; Dr. Betty L. Black, Committee Co-Chair; Dr. James N. Petitte, Committee Member; Dr. Chris M. Ashwell, Committee Member; Dr. Brenda J. Grubb, Committee Chair; Dr. Russell J. Borski, Committee Member
    In this study, the localization and possible functions of claudin tight junction proteins in bird and fish gastrointestinal tract were investigated. Claudin expression was detected in the chick intestine during the last week of embryonic development using microarrays and quantitative real time PCR analyses. Expression profiles differed among the claudins suggesting that they might play different roles in the establishment of intestinal tight junctions during embryonic development. Glucocorticoids are essential for the maturation of numerous tissues during embryonic development and are known to increase the integrity of tight junctions. This study reveals that treatment of 18-day old embryonic intestine with the synthetic glucocorticoid dexamethasone elevates mRNA levels of two claudins within 12 hours. Expression profiles of claudins were also analyzed in the gastrointestinal tract of Mozambique Tilapia. Immunohistochemistry and real-time PCR analyses revealed that various claudins were expressed in the tilapia gut in a tissue specific manner. Salinity transfer experiments indicated that salinity differentially regulates the expression of certain claudins suggesting a role for these proteins in osmoregulation.