PT - JOURNAL ARTICLE AU - Juan J. Fraire-Zamora AU - Johannes Jaeger AU - Jérôme Solon TI - Two consecutive microtubule-based epithelial seaming events mediate dorsal closure in the scuttle fly <em>Megaselia abdita</em> AID - 10.1101/229492 DP - 2017 Jan 01 TA - bioRxiv PG - 229492 4099 - http://biorxiv.org/content/early/2017/12/05/229492.short 4100 - http://biorxiv.org/content/early/2017/12/05/229492.full AB - Evolution of morphogenesis is generally associated with changes in genetic regulation. Here we report evidence indicating that dorsal closure, a conserved morphogenetic process in dipterans, evolved as the consequence of rearrangements in epithelial organization rather than signaling regulation. In Drosophila melanogaster, dorsal closure consists of a two-tissue system where the contraction of extraembryonic amnioserosa and a JNK/Dpp-dependent epidermal actomyosin cable result in microtubule-dependent seaming of the epidermis. We find that dorsal closure in Megaselia abdita, a three-tissue system comprising serosa, amnion and epidermis, differs in morphogenetic rearrangements despite conservation of JNK/Dpp signaling. In addition to an actomyosin cable, M. abdita dorsal closure is driven by the rupture and contraction of the serosa and the consecutive microtubule-dependent seaming of amnion and epidermis. Our study indicates that the evolutionary transition to a reduced system of dorsal closure involves simplification of the seaming process without changing the signaling pathways of closure progression.Impact Statement Evolutionary reduction in tissue number involves the simplification of the seaming process but not signaling during epithelial fusion.