Detection of chimeric alpha-defensin transcripts and peptides in mouse Paneth cells

Steven Timmermans ^1,2* Charlotte Wallaeys ^1,2 Somara De Beul ^1,2 Natalia Garcia Gonzalez ^1,2 Claude Libert ^1,2*

• ¹ Center for Inflammation Research, Flanders Institute for Biotechnology, Ghent, Belgium
• ² Ghent University, Ghent, East Flanders, Belgium

In mammals, Paneth cells, located in the crypts of the small intestine, produce antimicrobial peptides that keep the intestinal microbes under control. α-Defensins are the primary antimicrobial peptides produced by these cells. Bulk mRNA-seq on mouse Paneth cells reveals the existence of 28 protein coding Defa genes in mice, which is much greater than the amount of Defa genes in other species checked. Across our 148 bulk RNA-seq samples from sorted Paneth cells, approximately 85% of the total Paneth cell reads are assigned to Defa genes. Interestingly, we detected mRNAs composed of sequences from two different Defa genes. They are found in most of our experiments, and most of the 28 Defa gene mRNAs are involved in such chimeric Defa mRNAs. We estimate that the sum of all chimeric mRNAs does not exceed 0.3% of all Paneth cell mRNAs, which is not to be neglected. Even though the chimeric mRNAs are relatively unabundant, we did find chimeric peptides in Paneth cells by Mass Spectrometry. Finally, synthetic chimeric peptides appeared to have biological activity in lysing four different bacterial species.