Insights Into the Development of Gastrointestinal Brunner's Glands: Critical Stem Cells and Differentiation Factors
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Gastrointestinal Brunner's Glands are composed of secretory glandular epithelium and are located at the junction between the pylorus of the stomach and the duodenum of the small intestine. Brunner's Glands function by secreting a mucous-rich substance containing sodium bicarbonate and other important proteins in order to neutralize stomach acid and prevent damage to the intestinal epithelium. Prior research has shown that Brunner's Glands develop after birth, but little is known about the molecular mechanisms that control their development. Tumors of the in Brunner's Glands are known to occur in humans and understanding their developmei:it may assist in understanding how cancer and other pathologies in this gland arises. The aim of this study is to evaluate the stem cells and proteins that contribute to the development of the gland by using the laboratory mouse as our model organism. A stem cell marker known as Lrig I is a regulator of intestinal stem cell development and by using a technique known as "developmental lineage tracing," we have shown that Lrigl expressing stem cells contribute to the development of the Brunner's Gland. Developmental lineage tracing was also used in order to test for the contribution of Villin to the formation of the Brunner’s Gland, and this is another intestinal marker important for differentiation. Our results showed that Brunner’s Glands do not express Villin. In addition, since Brunner’s Glands are secretory glands, we hypothesized that a transcription factor called SPDEF is critical for proper development as it is an important protein for secretory gland formation. By analyzing the small intestines of transgenic mice with SPDEF mutations at multiple stages of maturity, we find that Brunner’s Glands were largely deformed and underdeveloped. These findings suggest that Brunner’s Glands are more closely related to the gastric epithelium, rather than the intestinal epithelium as has been previously postulated. Overall, the results of this study provide insight into the specific progenitor cells that contribute developmentally to the Brunner’s Gland, and shed light on the molecular mechanisms important for proper formation.