A microtubule-organizing center directing intracellular transport in the early mouse embryo

Abstract

The centrosome is the primary microtubule-organizing center (MTOC) of most animal cells; however, this organelle is absent during early mammalian development. Therefore, the mechanism by which the mammalian embryo organizes its microtubules (MTs) is unclear. We visualize MT bridges connecting pairs of cells and show that the cytokinetic bridge does not undergo stereotypical abscission after cell division. Instead, it serves as scaffold for the accumulation of the MT minus-end-stabilizing protein CAMSAP3 throughout interphase, thereby transforming this structure into a noncentrosomal MTOC. Transport of the cell adhesion molecule E-cadherin to the membrane is coordinated by this MTOC and is required to form the pluripotent inner mass. Our study reveals a noncentrosomal form of MT organization that directs intracellular transport and is essential for mammalian development.

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

“…9,11,12 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. The azobenzene-based Photostatins (PSTs), which can be reversibly photoswitched by low-intensity visible light between their biologically inactive E-isomers and their MT-inhibiting, colchicine-like Z isomers, were first reported in 2014.…”

“…All three reagent families have enabled highly spatiotemporally precise optical control over endogenous MT network integrity, MT polymerisation dynamics, cell division and cell death; and the PSTs have already been used in animals to resolve outstanding questions e.g. in mammalian development 13,14 and neuroscience 23 . These applications illustrate the power of photopharmacology to enable previously inaccessible studies of spatiotemporally anisotropic cytoskeletal processes without genetic engineering.…”