- Background: The conserved cytokine-induced apoptosis inhibitor-1 (CIAPIN1) gene has been implicated in several processes, such as apoptosis, cell division, angiogenesis and Fe/S protein biogenesis. In this study, we identified the Drosophila CIAPIN1 homologue (D-CIAPIN1) and studied its role in ovarian development. Results: We found that D-CIAPIN1 is conserved as it can complement the nonviability of the yeast CIAPIN1-deletion strain. Several D-CIAPIN1 alleles were identified, including one allele in which that codon encoding the highly conserved twin cysteine CX2C motif is mutated, demonstrating for the first time the importance of this motif to protein function. We demonstrated D-CIAPIN1 is an essential gene required for ovarian development. We found that D-CIAPIN1 female mutants are sterile, containing rudimentary ovaries. We noted a decrease in follicle cell numbers in D-CIAPIN1 mutant egg chambers. We further demonstrated that the decrease in follicle cell numbers in D-CIAPIN1 mutants is due to a reduced mitotic index and enhanced cell death. Conclusions: Our study reveals that D-CIAPIN1 is essential for egg chamber development and is required for follicle cell proliferation and survival. Developmental Dynamics 242:731–737, 2013. © 2013 Wiley Periodicals, Inc.