Drosophila Argonaute 1 and its miRNA biogenesis partners are required for oocyte formation and germline cell division

► Ago1 protein is highly enriched in Drosophila oocytes and follicle cells. ► Many Ago1 mutant egg chambers contain only 8 nurse cells without an oocyte. ► dicer-1, pasha and drosha exhibit similar effects on oogenesis as ago1. ► miRNAs play roles in oocyte formation and germline cell division in Drosophila.