48 Oral - Cell Biology I
Friday April 08, 8:30 AM - 8:45 AM

Authors:
Rachel Hodge ¹; Martin Resnik-Docampo ¹; Emma Edmond ¹; Fernando de la Torre ¹; Cecilia D'Alterio ¹; D. Leanne Jones ^1,2

Affiliations:
1) University of California Los Angeles, Los Angeles, CA; 2) University of California San Francisco, San Francisco, CA

Keywords:
t. cell junctions and adhesion; d. intestinal stem cells

In the intestine, the epithelial barrier is maintained by tight junctions (TJs) in mammals and septate junctions (SJs) in insects. The intestinal barrier allows para-cellular flow of water, ions and nutrients across the epithelium, while maintaining food matter and microbes inside the intestinal lumen. Age-related loss of intestinal barrier function has been found across multiple species, including Drosophila melanogaster and humans. The age-related causes of barrier dysfunction remain unknown. The tricellular junction (TCJ) is a specialized region of the SJ where three adjacent cells meet. Previous studies by our lab indicated that mis-localization of the TCJ protein Gliotactin (Gli) is correlated with aging. Depletion of Gli in young flies leads to loss of intestinal homeostasis, including increased intestinal stem cell (ISC) proliferation, a hallmark of aging. In the embryonic epithelium, the TCJ protein Bark is required to recruit Gli to the TCJ. Therefore, we hypothesized that Bark would be required for maintenance of intestinal homeostasis and barrier function, similar to Gli. Indeed, depletion of Bark from the TCJ of enterocytes in a young fly posterior midgut (PMG) led to an increase in ISC proliferation, accelerated age-associated intestinal barrier loss, and shortened lifespan, suggesting Bark is required for maintenance of intestinal homeostasis. Antibody staining for Gli and Bark shows a decrease in intensity at the TCJ in intestines from aged flies, with a modest, but significant, increase in Bark staining at the BCJ and in the cytoplasm. Previous RNAseq data indicated that expression of SJ protein genes, including Bark, is not decreased with age, and overexpression of Bark does not rescue age-associated loss of barrier function. Unlike in the embryonic epithelium, depletion of Gli disrupted proper localization of Bark to the TCJ in the PMG. In summary, the TCJ protein Bark is required at the TCJ to maintain intestinal homeostasis and barrier integrity in Drosophila. Our work on the mechanisms leading to loss of the intestinal barrier will provide insight into strategies to treat age-related gastrointestinal diseases, such as cancer.