Decoupling from yolk sac is required for extraembryonic tissue spreading in the scuttle fly Megaselia abdita

Abstract

Extraembryonic tissues contribute to animal development, which often entails spreading over embryo or yolk. Apart from changes in cell shape, the requirements for this tissue spreading are not well understood. Here, we analyze spreading of the extraembryonic serosa in the scuttle fly Megaselia abdita. The serosa forms from a columnar blastoderm anlage, becomes a squamous epithelium, and eventually spreads over the embryo proper. We describe the dynamics of this process in long-term, whole-embryo time-lapse recordings, demonstrating that free serosa spreading is preceded by a prolonged pause in tissue expansion. Closer examination of this pause reveals mechanical coupling to the underlying yolk sac, which is later released. We find mechanical coupling prolonged and serosa spreading impaired after knockdown of M. abdita Matrix metalloprotease 1. We conclude that tissue–tissue interactions provide a critical functional element to constrain spreading epithelia.

Fish primary embryonic pluripotent cells assemble into retinal tissue mirroring in vivo early eye development

“…The organoids were mounted in 1% low melting agarose (StarPure Low Melt Agarose, Cat#N3103-0100, StarLab GmbH) inside an FEP tube (Karl Schupp AG) fixed on glass capillaries. Four volumes (two cameras and two rotation angles) were acquired with the 25× detection setup ( Caroti et al, 2018 ), 1 µm z step size for three channels: GFP (Atoh7) 488 nm excitation laser at 40% intensity, 525/50 nm emission filter, 600 ms exposure time; RFP (β-catenin) 561 nm excitation laser at 40% intensity, 607/70 nm emission filter, 600 ms exposure time; far Red (HuC/D) 642 nm excitation laser at 50% intensity, 579/40 nm emission filter, 1000 ms exposure time. The volumes were fused with Luxendo Image fusion software.…”

Enhanced in vivo-imaging in medaka by optimized anaesthesia, fluorescent protein selection and removal of pigmentation

“…Medaka embryos were anesthetized with 1x Tricaine or by α-Bungarotoxin mRNA injection and stacks were acquired in a MuVi-SPIM (multiview selective plane illumination microscope) [15,16,52] as described before [53] for the 25x detection setup, with the addition of a 488 nm illumination and a corresponding 525/50 bandpass filter. For the measurements of fluorescence intensity the resulting images were divided by the control channel, masked by the Otsu algorithm [54] and subsequently measured.…”

How two extraembryonic epithelia became one: serosa and amnion features and functions of Drosophila 's amnioserosa

“…The amnioserosa is found in schizophoran fly species [6,21,22], a large subgroup of the Cyclorrhapha that radiated in the Tertiary [3,23], while representatives of basal-branching cyclorrhaphan lineages, such as the hover fly Episyrphus balteatus (Syrphidae) and the scuttle fly Megaselia abdita (Phoridae), develop with a serosa and a vestigial amnion (figure 1) [22,24–26]. These findings suggest that the evolution of a vestigial amnion preceded the evolution of the amnioserosa and that the organization of extraembryonic tissue in lower cyclorrhaphan fly species reflects a condition that preceded the origin of the amnioserosa; hence these species are of special importance for reconstructing the evolution of the amnioserosa.…”

“…In Megaselia , serosa cells are specified at the centre of the extraembryonic domain, which straddles the dorsal midline [6]. After gastrulation, these cells spread out underneath the eggshell and close about the extended germ band (figure 1) [22,26]. During this process, the amnion folds over the posterior germ band and—to a lesser degree—over the leading edge of the lateral epidermis [22,26].…”

“…After gastrulation, these cells spread out underneath the eggshell and close about the extended germ band (figure 1) [22,26]. During this process, the amnion folds over the posterior germ band and—to a lesser degree—over the leading edge of the lateral epidermis [22,26]. However, once dissociated from the serosa, the amnion cells relocate to the yolk sac surface and align along the leading edge of the epidermis (figures 2 and 3) [24,33].…”