RT Journal Article SR Electronic T1 A revised understanding of Tribolium morphogenesis further reconciles short and long germ development JF bioRxiv FD Cold Spring Harbor Laboratory SP 232751 DO 10.1101/232751 A1 Matthew A. Benton YR 2018 UL http://biorxiv.org/content/early/2018/04/15/232751.abstract AB In Drosophila melanogaster, the germband forms directly on the egg surface and solely consists of embryonic tissue (termed long germ development). In contrast, most insect embryos undergo a complicated set of tissue rearrangements to generate a condensed, bilayered germband (termed short/intermediate germ development). The ventral side of the germband is embryonic, while the dorsal side is thought to be an extraembryonic tissue called the amnion. While this tissue organisation has been accepted for decades, and has been widely reported in insects, its accuracy has not been directly tested in any species. Using live cell tracking and differential cell labelling in the short germ beetle Tribolium castaneum, I show that most of the cells previously thought to be amnion actually give rise to large parts of the embryo. This process occurs via the dorsal-to-ventral flow of cells and contributes to germband extension. In addition, I show that true ‘amnion’ cells in Tribolium originate from a small region of the blastoderm. Together, my findings show that development in the short germ embryos of Tribolium and the long germ embryos of Drosophila is more similar than previously proposed. Dorsal-to-ventral cell flow also occurs in Drosophila during germband extension, and I argue that the flow is driven by a conserved set of underlying morphogenetic events in both species. Furthermore, the revised Tribolium fatemap that I present is far more similar to that of Drosophila than the classic Tribolium fatemap. Lastly, my findings show that there is no qualitative difference between the structures of the blastoderm and the short/intermediate germ germband. As such, the same tissue patterning mechanisms could function continuously throughout the cellularised blastoderm and germband stages, and easily shift between them over evolutionary time.