Expression of ABC transporters in the Drosophila testis stem cell niche: Comparison of two approaches

The ABC transporter gene family encodes proteins that form transmembrane channels and hydrolyze ATP to pump various substrates into and out of cells. Adult stem cell populations in numerous mammalian tissues express members of this gene family in order to efflux toxins or vital dyes, thereby conferring the "side population" trait, and cancer stem cells exhibit multidrug resistance upon expression of members of this gene family. In this study we investigated the expression of ABC transporters in a leading model organism stem cell niche, the Drosophila testis. We screened enhancer and gene trap lines with insertions near ABC transporter genes and identified six transporters with tissue-specific expression in the testis (ABCB7, MRP, rdog, CG3164, CG31121, and CG9663). Contrary to our expectation, we did not observe mostly stem cell-restricted expression patterns for these genes. We also report the expression patterns of ABC transporter genes in the testis from the published Fly Cell Atlas consortium single-cell sequencing of the testis (Li et al., 2022). Comparison of the expression levels and patterns of the six positive genes from the enhancer/gene trap screen with the FCA data showed only weak correlation between the two gene expression approaches. While there are reasons that the techniques might show different results, our work highlights the need for caution in over-reliance on single techniques to investigate gene expression.