Thorax closure in Drosophila is a process during adult morphogenesis in which the anterior ends of the presumptive notum of the two wing imaginal discs fuse to make a seamless thorax. Similar to dorsal closure during embryogenesis, this process is regulated by plegic and JNK signaling pathways. Despite the fact that Peripodial Membrane (PM) cells do not contribute to the formation of any adult structure, they are known to facilitate the process of thorax closure. Here we show that JNK signaling is activated only in a subset of PM cells, known as medial edge cells. While the mechanism that activates JNK signaling specifically in the medial edge cells of the PM is still not understood, the results presented here show that the pair rule gene odd skipped is required to ensure that JNK signaling is not activated anywhere else in the wing disc. Medial edge cells of the PM are elongated in shape, while the remaining PM cells are hexagonal. Down regulation of JNK signaling in the medial edge cells results in defective thorax closure in adult flies. It also causes the transformation of the morphology of medial edge cells into hexagonal shape. Conversely, activation of JNK signaling in hexagonal cells of the PM causes transformation of their morphology to elongated shape. Thus, similar to dorsal closure during embryogenesis, JNK-mediated elongation of medial edge cells is functionally correlated to the process of thorax closure.