title: Soft viscoelastic properties of nuclear actin age oocytes due to gravitational creep.
abstract: The actin cytoskeleton helps maintain structural organization within living cells. In large X. laevis oocytes, gravity becomes a dominant force and is countered by a nuclear actin network that prevents liquid-like nuclear bodies from immediate sedimentation and coalescence. However, nuclear actin's mechanical properties, and how they facilitate the stabilization of nuclear bodies, remain unknown. Using active microrheology, we find that nuclear actin forms a weak viscoelastic network, with a modulus of roughly 0.1 Pa. Embedded probe particles subjected to a constant force exhibit continuous displacement, due to viscoelastic creep. Gravitational forces also cause creep displacement of nuclear bodies, resulting in their asymmetric nuclear distribution. Thus, nuclear actin does not indefinitely support the emulsion of nuclear bodies, but only kinetically stabilizes them by slowing down gravitational creep to ~2 months. This is similar to the viability time of large oocytes, suggesting gravitational creep ages oocytes, with fatal consequences on long timescales.
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Marina
authors.initials: M
authors.lastname: Feric
authors.affiliation: Lewis-Sigler Institute for Integrative Genomics and Joseph Henry Laboratories of Physics, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Chase P
authors.initials: CP
authors.lastname: Broedersz
authors.affiliation: Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Clifford P
authors.initials: CP
authors.lastname: Brangwynne
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D016922:Cellular Senescence; D004548:Elasticity; D006112:Gravitation; D008954:Models, Biological; D009865:Oocytes / Q000378:metabolism*; D015388:Organelles / Q000378:metabolism; D012212:Rheology; D014783:Viscosity; D014982:Xenopus laevis
chemical_list: D000199:Actins