# Gene Expression Analysis before and after the Pelvic Flexure in the Epithelium of the Equine Hindgut

## TL;DR

This study compares gene expression patterns in the equine hindgut around the pelvic flexure to understand how it influences microbial communities and gut physiology.

## Contribution

The study provides new insights into gene expression differences in the equine hindgut epithelium, particularly around the pelvic flexure.

## Key findings

- Most genes are expressed across all hindgut tissues, but some show tissue-specific expression patterns.
- Genes in the pelvic flexure are associated with immune functions and signaling processes.
- Tissue-specific genes in the ventral and dorsal colons relate to communication and regulatory functions.

## Abstract

The equine hindgut plays a central role in digesting forage by hosting a complex community of microorganisms responsible for fermenting and digesting plant fibers. Research has shown that the different compartments of the hindgut have unique microbial communities. The pelvic flexure, an anatomic structure that separates segments of the hindgut and prevents backflow, seems to help maintain these distinct communities. How it achieves this has yet to be fully understood. While much is known about the hindgut’s anatomy and digestion, only a few studies have investigated gene expression patterns and differences in the tissues around the pelvic flexure. In this study, we used next-generation RNA sequencing to analyze and compare gene expression in the pelvic flexure and the ventral and dorsal segments of the large colon in horses. This knowledge can help researchers, veterinarians, and horse owners better understand the equine hindgut’s physiology and how horses interact with the microbial communities there and could provide insights for managing healthy horses or treating horses with digestive issues.

Previous research demonstrated the distribution of distinct microbial communities in the equine hindgut surrounding the pelvic flexure. The current study evaluated gene expression in epithelial tissues surrounding the pelvic flexure to characterize patterns that might correlate with microbial distribution. Gene expression was determined by analyzing RNA sequence data from the pelvic flexure, the left and right ventral colon, and the left and right dorsal colon. An average of 18,330 genes were expressed across the five tissues sampled. Most of the genes showed some level of expression in all five tissues. Tissue-restricted patterns of expression were also observed. Genes with restricted expression in the left ventral and left dorsal colons have communication, signaling, and regulatory functions that correlate with their known physiology. In contrast, genes expressed exclusively in the pelvic flexure have diverse functions. The ontology of genes differentially expressed between the pelvic flexure and the surrounding tissues was associated with immune functions and signaling processes. Despite being non-significant, these enrichment trends were reinforced by the functions of statistically significant expression differences between tissues of the hindgut. These results provide insight into the physiology of the equine hindgut epithelium that might influence the microbiota and its distribution.