Abstract

The evolution of morphogenesis is generally assumed to be associated with changes in genetic patterns that lead to the spatial reorganization of tissues. I will present a case study where rearrangements of epithelial organization occur without major changes in genetic patterning. In Drosophila melanogaster, the process of dorsal closure consists of the fusion of opposing epithelial sheets where a contractile extraembryonic amnioserosa and a JNK /Dpp-dependent epidermal actomyosin cable result in a microtubule-dependent seaming of the epidermis. In the scuttle fly Megaselia abdita, dorsal closure must occur in the presence of a separate serosa, amnion and epidermis. It differs from Drosophila in morphogenetic rearrangements despite conservation of the JNK /Dpp signaling pathway. Using a quantitative approach in a non-model organism, we show that dorsal closure in M. abdita is driven by the rupture and contraction of the serosa, an epidermal actomyosin cable and the consecutive microtubule-dependent seaming of amnion and epidermis. Using high-resolution time-lapse imaging, immunostaining and molecular tools, we obtained evidence indicating that the evolutionary transition to a reduced system of dorsal closure involves the simplification of the seaming process without changing the signaling pathways of closure progression.