Researcher ORCID Identifier

0000-0001-7822-6913

Graduation Year

2020

Document Type

Open Access Senior Thesis

Degree Name

Bachelor of Arts

Department

W.M. Keck Science Department

Second Department

Molecular Biology

Reader 1

Emily Wiley

Terms of Use & License Information

Terms of Use for work posted in Scholarship@Claremont.

Abstract

The lining of the colon, or colonic epithelium, is a very dynamic and highly regulated tissue in the human body. Colonic stem cells are a key component of this tissue, and they make up the stem cell niche, which is found at the base of the colonic crypt. Regeneration of the colonic epithelium, which occurs on a weekly basis, is a complex process, and proteins responsible for directing regeneration are still being discovered. Two critical regulatory proteins, Lrig1 and Lrig3, have been shown to modulate the EGFR pathway, a key signaling pathway for growth, differentiation, and regeneration. Data from the Zemper Lab found Lrig1, a colonic stem cell marker, to be expressed at significantly higher locations in the crypts of Lrig3-null mice, suggesting an expansion of the colonic stem cell niche. Morphologically, Lrig3-/- mice exhibit an increase in total mucosal area, accompanied by a significant increase in the number of crypt cells as revealed by H&E staining. We hypothesized that an increase in colon crypt height correlates with an expansion of the stem cell niche to higher locations in the crypt. If this hypothesis is true, we would predict that, accompanying the increase in stem cells at higher crypt locations observed in Lrig3-/- mice, an increase in the number of differentiated cells, such as support cells, may be observed in the expanded stem cell niche. To test this prediction, we quantified and characterized colonic stem and differentiated cell markers, using immunostaining and fluorescence microscopy. We characterized crypts of Lrig3-/- mice based on cellular composition, heterogeneity, and positional data, comparing these features with those of wildtype mice. We found that the increase in mucosal area in Lrig3-/- crypts can be attributed to an increase in the number of cells. We also found that there was a significant increase in the number of support cells inside the stem cell niche and no significant change in the number of support cells outside the stem cell niche of Lrig3-/- crypts. This supports our hypothesis that an increase in colon crypt height correlates with an expansion of the stem cell niche. Our results may have further implications for growth and homeostasis in the crypt, which are key features of regeneration. These findings may provide insight about colon recovery from inflammatory diseases, such as ulcerative colitis, which affect a large percent of the human population.

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