(38) Actin Organizes Mitotic Chromosomes During Preimplantation Mouse Development

Blake Hernandez¹, Piotr Tetlak¹, Ana Domingo-Muelas¹, Hiroki Akizawa¹, Robin M. Skory¹, Goli Ardestani², Mate Biro³, Xiaolei Liu¹, Stephanie Bissiere¹, Denny Sakkas², Nicolas Plachta¹

¹ Department of Cell and Developmental Biology, Institute for Regenerative Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA

² Boston IVF-Eugin Group, Waltham, MA, 02451, USA

³ EMBL Australia, University of New South Wales, Australia

 

Abstract Text:

Following fertilization, the preimplantation embryo undergoes successive rounds of mitotic divisions and must accurately propagate its genetic material to ensure successful development. However, early mammalian embryos lack efficient spindle assembly mechanisms, and it thus remains unclear how error-free chromosome segregation is achieved. Here, we image early mouse embryos and identify a network of formin-dependent nuclear actin cables. Upon mitotic entry, this network organizes chromosomes at the nuclear periphery via Myosin-10 and undergoes contraction, effectively gathering chromosomes towards the cell center. Network contraction is driven by filament depolymerization and is Myosin II-independent. Furthermore, we identify an Arp2/3–dependent network of branched actin filaments which encloses the metaphase spindle and attenuates its elongation. Together with our observation of similar actin assemblies in human embryos, our findings reveal that actin ensures mitotic fidelity during early mammalian development.