Abstract
SummaryInsect embryos complete the outer form of the body via dorsal closure (DC) of the epidermal flanks, replacing the transient extraembryonic (EE) tissue. Cell shape changes and morphogenetic behavior are well characterized for DC in Drosophila, but these data represent a single species with a secondarily reduced EE component (the amnioserosa) that is not representative across the insects. Here, we examine DC in the red flour beetle, Tribolium castaneum, providing the first detailed, functional analysis of DC in an insect with complete EE tissues (distinct amnion and serosa). Surprisingly, we find that differences between Drosophila and Tribolium DC are not restricted to the EE tissue, but also encompass the dorsal epidermis, which differs in cellular architecture and method of final closure (zippering). We then experimentally manipulated EE tissue complement via RNAi for Tc-zen1, allowing us to eliminate the serosa and still examine viable DC in a system with a single EE tissue (the amnion). We find that the EE domain is particularly plastic in morphogenetic behavior and tissue structure. In contrast, embryonic features and overall kinetics are robust to Tc-zen1RNAi manipulation in Tribolium and conserved with a more distantly related insect, but remain substantially different from Drosophila. Although correct DC is essential, plasticity and regulative, compensatory capacity have permitted DC to evolve within the insects. Thus, DC does not represent a strong developmental constraint on the nature of EE development, a property that may have contributed to the reduction of the EE component in the fly lineage.
Highlights
In the second half of embryogenesis, the insect embryo closes its body when the left and right flanks expand up to and meet at the dorsal midline, a process known as dorsal closure (DC)
Summary Insect embryos complete the outer form of the body via dorsal closure (DC) of the epidermal flanks, replacing the transient extraembryonic (EE) tissue
Cell shape changes and morphogenetic behavior are well characterized for DC in Drosophila, but these data represent a single species with a secondarily reduced EE component that is not representative across the insects
Summary
In the second half of embryogenesis, the insect embryo closes its body when the left and right flanks expand up to and meet at the dorsal midline, a process known as dorsal closure (DC). They replace extraembryonic (EE) tissue that had served as a provisional cover over the yolk. This process has been well studied in the fruit fly Drosophila melanogaster Having first developed to enclose the embryo, the EE membranes later actively withdraw in a precise way prior to their elimination during DC. Throughout these morphogenetic rearrangements, the serosa and amnion are distinct players, such that DC is a threetissue system (embryo, amnion, and serosa) in most insects
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