The Male Accessory Gland: A novel model to evaluate new ER stress genes. Clement Y. Chow, Andrew G. Clark, Mariana F. Wolfner. Dept Molec Biol & Gen, Cornell Univ, Ithaca, NY.

   The endoplasmic reticulum (ER) is a large organelle that is responsible for synthesis, maturation, and delivery of a variety of proteins essential for cellular function. ER dysfunction occurs when misfolded proteins accumulate in the ER lumen, causing ER stress. The cell responds to ER stress with the unfolded protein response (UPR). The UPR can return the ER to homeostasis by attenuating protein synthesis, activating transcriptional signaling cascades, and refolding or degrading misfolded proteins in the ER. ER stress can be a primary cause or secondary effect of many human diseases. Drosophila is an ideal, if underutilized genetic model with which to dissect the conserved ER stress response. In a previous screen of the DGRP, we found a large number of genes contributing to genetic variation in ER stress response in Drosophila. Over 50% of the genes we found had no previously known function in ER stress response. Additionally, ~50%; of these putative ER stress genes were essential for viability. To further characterize the function of these new genes in the ER stress response, we developed an in vivo system. We use the male accessory gland (AG) as our assay system. This AG synthesizes and secretes numerous proteins that are transferred to the female during mating. Because of its large secretory role, the AG requires optimal ER function. Indeed, the AG has the highest basal expression of genes that are upregulated under ER stress conditions. We subjected the AG to ER stress by locally expressing a misfolded rhodopsin or by ex vivo treatment with tunicamycin. Both ER-stress-inducing treatments impaired AG function: accessory gland protein production was reduced, as was male fertility. Our results identified a set of phenotypic, transcriptional, and translational markers indicative of ER stress in the AG. We show that these markers accurately predict ER stress when known ER stress genes such as BiP are perturbed in an AG-specific manner. Thus, the AG will be a useful and quantitative model for efficiently testing the novel ER stress genes identified in our variation studies.