Cup is essential for mRNA translational repression during early oogenesis.

Study of the timing and location for mRNA translation across model systems has begun to shed light on molecular events fundamental to such processes as intercellular communication, morphogenesis, and body pattern formation. In , the posterior mRNA determinant, , is transcribed maternally but translated only when properly localized at the oocyte's posterior cortex. Two effector proteins, Bruno1 and Cup, mediate steps of mRNA regulation. The current model in the field identifies Bruno1 as necessary for Cup's recruitment to mRNA and indispensable for 's translational repression. We now report that this Bruno1-Cup interaction leads to precise mRNA regulation during early oogenesis and, importantly, the two proteins mutually influence each other's mRNA expression and protein distribution in the egg chamber. We show that these factors stably associate with mRNA . Cup associates with mRNA without Bruno1, while surprisingly Bruno1's stable association with mRNA depends on Cup. We demonstrate that the essential factor for mRNA repression in early oogenesis is Cup, not Bruno1. Furthermore, we find that Cup is a key P-body component that maintains functional P-body morphology during oogenesis and is necessary for mRNA's association with P-bodies. Therefore, Cup drives the translational repression and stability of mRNA. These experimental results point to a regulatory feedback loop between Bruno 1 and Cup in early oogenesis that appears crucial for mRNA to reach the posterior pole and its expression in the egg chamber for accurate embryo development.