Expanding Actin Rings Zipper the Mouse Embryo for Blastocyst Formation

Abstract

Transformation from morula to blastocyst is a defining event of preimplantation embryo development. During this transition, the embryo must establish a paracellular permeability barrier to enable expansion of the blastocyst cavity. Here, using live imaging of mouse embryos, we reveal an actin-zippering mechanism driving this embryo sealing. Preceding blastocyst stage, a cortical F-actin ring assembles at the apical pole of the embryo's outer cells. The ring structure forms when cortical actin flows encounter a network of polar microtubules that exclude F-actin. Unlike stereotypical actin rings, the actin rings of the mouse embryo are not contractile, but instead, they expand to the cell-cell junctions. Here, they couple to the junctions by recruiting and stabilizing adherens and tight junction components. Coupling of the actin rings triggers localized myosin II accumulation, and it initiates a tension-dependent zippering mechanism along the junctions that is required to seal the embryo for blastocyst formation.

H3K27me3 is an epigenetic barrier while KDM6A overexpression improves nuclear reprogramming efficiency

“…Consistent with the aforementioned studies, we also discovered that cell adhesion-related genes, including CDH1, were up-regulated by KDM6A overexpression in bovine embryos. Importantly, during preimplantation embryo development, adherens and tight junctions coordinately establish the first internal cavity of the embryo to transform the morula into a blastocyst (54); perturbation of these junctions leads to defects in blastocyst formation (55)(56)(57). These results provide a basis for investigating the mechanism of the first cell fate determination during embryonic development in mammals.…”

Hemithioindigos for Cellular Photopharmacology: Desymmetrised Molecular Switch Scaffolds Enabling Design Control over the Isomer‐Dependency of Potent Antimitotic Bioactivity

“…Tubulin is one of many survival‐critical intracellular proteins whose activity it has not been possible to regulate directly by genetic methods, such as by the creation of optogenetic tubulin constructs, that would give the experimenter biologically meaningful (spatiotemporally precise) control over microtubule structure and biology. In this context, by enabling such previously impossible studies, the azobenzene‐based photopharmaceutical PST‐1 (azocombretastatin) has already achieved significant applications, leveraging the spatially and temporally precise photoreversible switching of its bioactivity . Alternative photoswitchable scaffolds for tubulin photocontrol that could expand the chemical substituent tolerance of practical tubulin photopharmaceuticals, as well as enable the opposite photoresponse (dark‐active) from PST‐1 and so access conceptually distinct applications, would also be of extensive interest to the cytoskeleton research community.…”

“…The conceptually unique biological research applications of such photopharmaceuticals (especially in multicellular systems) then typically involve patterning the isomers in space and/or over time, by two‐colour illuminations. Such spatiotemporally reversible two‐colour patterning has notably allowed complex studies in embryology and development, where precise bidirectional switching was employed to subcellularly resolve the organisation of tubulin and its interplay with the actin cytoskeleton in early mouse embryos. In such bidirectional‐switching applications, it is crucial for practical success that the metastable isomer be designed to be the more bioactive form, so that maintaining a “non‐inhibited” background of activity in the organism does not require repeated illuminations scanning through the entire sample (but only localised illuminations in the area to be affected), and so that moderate spontaneous relaxation rates can help to suppress the accumulation of background levels of the active isomer.…”

“…The requirement for correctly functional microtubule dynamics during mitosis has driven extensive work on targeted and selective microtubule‐binding agents as “antimitotic” cancer chemotherapeutics, including paclitaxel, epothilone and vinca alkaloids . In research, the sheer breadth and spatiotemporal complexity of microtubule‐dependent biological roles presents an excellent opportunity for photopharmacological intervention, and microtubule‐targeting photopharmaceuticals such as PST‐1 have quickly moved on from chemical proof‐of‐concept to find diverse cellular and animal research applications . Due to the massive clinical utility of microtubule‐binding agents in cancer therapy, as well as the systemic side‐effects of conventional antimitotics, it is also of extensive interest to find more potent photoswitchable microtubule inhibitors and evaluate whether they can be guided by localised tumour illumination to act as tumour‐specific antimitotics that spare healthy tissues from chemotherapeutic damage.…”

Photoswitchable microtubule stabilisers optically control tubulin cytoskeleton structure and function

“…9,10 Photopharmaceuticals conceptually enable studies not otherwise accessible to biology, marrying the spatiotemporal precision of light application known from optogenetics, to the flexibility and system-independence of exogenous small molecule inhibitors, in a way that particularly favours noninvasive studies of temporally-regulated, spatially-anisotropic biological systems, such as the MT cytoskeleton. 9,11,12 Photopharmaceuticals have succeeded in delivering a measure of optical control over a broad range of biochemical and biological phenomena, with early cell-free studies now supplanted by applications in cellulo and recently in vivo. [13][14][15][16] In the cytoskeleton field, photopharmaceutical analogues of the MT destabiliser colchicine were recently developed, to begin addressing the need for spatiotemporally precise MT cytoskeleton studies.…”