Spire-Type Actin Nucleators Cooperate with Formin-2 to Drive Asymmetric Oocyte Division

• Published in: Current biology Vol. 21; no. 11; pp. 955 - 960
• Main Authors: Pfender, Sybille, Kuznetsov, Vitaliy, Pleiser, Sandra, Kerkhoff, Eugen, Schuh, Melina
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 07.06.2011; Cell Press
• Subjects: actin; Actins - metabolism; Animals; Cell Division - genetics; Cell Division - physiology; Cell Polarity; chromosomes; eggs; extrusion; meiosis; Mice; Microfilament Proteins - antagonists & inhibitors; Microfilament Proteins - genetics; Microfilament Proteins - metabolism; Microfilament Proteins - physiology; microfilaments; Nerve Tissue Proteins - antagonists & inhibitors; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - physiology; Nuclear Proteins - metabolism; Nuclear Proteins - physiology; oocytes; Oocytes - cytology; Oocytes - metabolism; Oocytes - ultrastructure; RNA Interference; Spindle Apparatus - metabolism; Spindle Apparatus - ultrastructure
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2011.04.029

Oocytes mature into eggs by extruding half of their chromosomes in a small cell termed the polar body. Asymmetric oocyte division is essential for fertility [1], but despite its importance, little is known about its mechanism. In mammals, the meiotic spindle initially forms close to the center of the oocyte. Thus, two steps are required for asymmetric meiotic division: first, asymmetric spindle positioning and second, polar body extrusion. Here, we identify Spire1 and Spire2 as new key factors in asymmetric division of mouse oocytes. Spire proteins are novel types of actin nucleators that drive nucleation of actin filaments with their four WH2 actin-binding domains [2–6]. We show that Spire1 and Spire2 first mediate asymmetric spindle positioning by assembling an actin network that serves as a substrate for spindle movement. Second, they drive polar body extrusion by promoting assembly of the cleavage furrow. Our data suggest that Spire1 and Spire2 cooperate with Formin-2 (Fmn2) to nucleate actin filaments in mouse oocytes and that both types of nucleators act as a functional unit. This study not only reveals how Spire1 and Spire2 drive two critical steps of asymmetric oocyte division, but it also uncovers the first physiological function of Spire-type actin nucleators in vertebrates. [Display omitted] ► Spire1 and Spire2 mediate asymmetric spindle positioning in mouse oocytes ► They assemble an actin network that serves as a substrate for spindle movement ► Spire1 and Spire2 drive polar body extrusion by promoting cleavage furrow assembly ► Spire1 and Spire2 cooperate with Formin-2 in a functional unit