Interference in xbp1 gene expression induces defective cell differentiation and sensory organ development in Drosophila

The X-box binding protein 1 (Xbp1) is a transcription factor that is important in the unfolded protein response to protect cells from endoplasmic reticulum (ER) stress and is implicated in several other biological processes, including liver growth and B lymphocyte differentiation. Although the cellular function of Xbp1 has been well studied, its developmental role remains to be elucidated. In the present study, we investigated the developmental role of Drosophila xbp1 using an RNAi-mediated gene silencing system. When xbp1 gene expression was specifically interfered with in developing tissues, such as wing and eye during larval growth, the tissues were strongly deformed. Cell death was not observed in these tissues, and this phenotype was not rescued by the overexpression of Drosophila inhibitor of apoptosis protein 1 (DIAP1), a caspase inhibitor, indicating that these developmental defects are not associated with apoptosis. Furthermore, changes were not observed in cell cycle progression and Jun-N-terminal kinase activation in tissues whose xbp1 gene expression was interfered with. Rather, the xbp1 gene silencing resulted in defective cell differentiation and supernumerary of sensory organ precursors. These results suggest the inability of xbp1 gene silencing to induce strong ER stress and the importance of Drosophila Xbp1 in cell fate determination and sensory organ development.