The Drosophila intestine is an excellent system for elucidating mechanisms regulating stem cell behavior. Here we show that the septate junction (SJ) protein Neuroglian (Nrg) is expressed in intestinal stem cells (ISCs) and enteroblasts (EBs) within the fly intestine. SJs are not present between ISCs and EBs, suggesting Nrg plays a different role in this tissue. We reveal that Nrg is required for ISC proliferation in young flies, and depletion of Nrg from ISCs and EBs suppresses increased ISC proliferation in aged flies. Conversely, overexpression of Nrg in ISC and EBs promotes ISC proliferation, leading to an increase in cells expressing ISC/EB markers; in addition, we observe an increase in epidermal growth factor receptor (Egfr) activation. Genetic epistasis experiments reveal that Nrg acts upstream of Egfr to regulate ISC proliferation. As Nrg function is highly conserved in mammalian systems, our work characterizing the role of Nrg in the intestine has implications for the treatment of intestinal disorders that arise due to altered ISC behavior.

SummaryThe Drosophila melanogaster intestine is an excellent system for elucidating mechanisms regulating stem cell behavior under homeostatic conditions or in response to injury, stress, or ageing. Here we show that the septate junction (SJ) protein Neuroglian (Nrg) is expressed in intestinal stem cells (ISCs) and daughter enteroblasts (EBs) within the fly midgut, the equivalent of the mammalian small intestine. Although Nrg localizes to the plasma membrane, SJs are not present between ISC/EBs, suggesting Nrg plays a different role in this tissue. Generation of ISCs homozygous for a null allele of Nrg revealed that Nrg is required for ISC proliferation in young flies, and depletion of Nrg from ISCs/EBs was able to suppress the increase in ISC proliferation with age. Conversely, overexpression of Nrg in ISC/EBs was sufficient to drive ISC proliferation, leading to an increase in cells expressing ISC/EB markers. In addition, we observed an increase in EGFR activation. Genetic epistasis experiments revealed that Nrg acts upstream of EGFR in the midgut to regulate ISC proliferation. As Nrg function is highly conserved in mammalian systems, our work characterizing the role of Nrg in the intestine has implications for the etiology and treatment of intestinal disorders due to altered ISC behavior.