upstream of Hippo signaling
NCBI Summary:
Spire proteins, such as SPIRE1, are highly conserved between species. They belong to the family of Wiskott-Aldrich homology region-2 (WH2) proteins, which are involved in actin organization (Kerkhoff et al., 2001 [PubMed 11747823]).[supplied by OMIM, Mar 2008]
General function
Chromosome organization
Comment
Cellular localization
Nuclear
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Ovarian function
Oogenesis
, First polar body extrusion
Comment
Spire localization via zinc finger-containing domain is crucial for the asymmetric division of mouse oocyte. Jo YJ et al. (2018) Zinc plays an essential role in mammalian oocyte maturation, fertilization, and early embryogenesis, and depletion of zinc impairs cell cycle control, asymmetric division, and cytokinesis in oocyte. We report that zinc, via the actin nucleator Spire, acts as an essential regulator of the actin cytoskeleton remodeling during mouse oocyte maturation and fertilization. Depletion of zinc in the mouse oocyte impaired cortical and cytoplasmic actin formation. Spire is colocalized with zinc-containing vesicles via its zinc finger-containing Fab1, YOTB, Vac 1, EEA1 (FYVE) domain. Improper localization of Spire by zinc depletion or mutations in the FYVE domain impair cytoplasmic actin mesh formations and asymmetric division and cytokinesis of oocyte. All 3 major domains of the Spire are required for its proper localization and activity. After fertilization or parthenogenetic activation, Spire localization was dramatically altered following zinc release from the oocyte. Collectively, our data reveal novel roles for zinc in the regulation of the actin nucleator Spire by controlling its localization in mammalian oocyte.-Jo, Y.-J., Lee, I.-W., Jung, S.-M., Kwon, J., Kim, N.-H., Namgoong, S. Spire localization via zinc finger-containing domain is crucial for the asymmetric division of mouse oocyte.//////////////////
Role of the C-terminal extension of Formin 2 in its activation by Spire and processive assembly of actin filaments. Montaville P et al. (2015) Formin 2 (Fmn2), a member of the FMN family of formins, plays an important role in early development. This formin cooperates with profilin and Spire, a WH2 repeat protein, to stimulate assembly of a dynamic cytoplasmic actin meshwork that facilitates translocation of the meiotic spindle in asymmetric division of mouse oocytes. The KIND domain of Spire directly interacts with the C-terminal extension of the FH2 domain of Fmn2, called FSI. This direct interaction is required for the synergy between the two proteins in actin assembly. We have recently demonstrated how Spire, which caps barbed ends via its WH2 domains, activates Fmn2. Fmn2 by itself associates very poorly to filament barbed ends, but is rapidly recruited to Spire-capped barbed ends via the KIND domain, and subsequently displaces Spire from the barbed end to elicit rapid processive assembly from profilin-actin. Here we address the mechanism by which Spire and Fmn2 compete at barbed ends and the role of FSI in orchestrating this competition as well as the processivity of Fmn2. We have combined microcalorimetric, fluorescence and hydrodynamic binding assays, as well as bulk solution and single filament measurements of actin assembly, to show that removal of FSI converts Fmn2 into a capping protein. This activity is mimicked by association of KIND to Fmn2. In addition, FSI binds actin at filament barbed ends as a weak capper and plays a role in displacing the WH2 domains of Spire from actin, thus allowing the association of actin-binding regions of FH2 to the barbed end.//////////////////
Expression regulated by
Comment
Ovarian localization
Oocyte
Comment
Direct interaction between two actin nucleators is required in Drosophila oogenesis. Quinlan ME 2013 et al.
Controlled actin assembly is crucial to a wide variety of cellular processes, including polarity establishment during early development. The recently discovered actin mesh, a structure that traverses the Drosophila oocyte during mid-oogenesis, is essential for proper establishment of the major body axes. Genetic experiments indicate that at least two proteins, Spire (Spir) and Cappuccino (Capu), are required to build this mesh. The spire and cappuccino genetic loci were first identified as maternal effect genes in Drosophila. Mutation in either locus results in the same phenotypes, including absence of the mesh, linking them functionally. Both proteins nucleate actin filaments. Spir and Capu also interact directly with each other in vitro, suggesting a novel synergistic mode of regulating actin. In order to understand how and why proteins with similar biochemical activity would be required in the same biological pathway, genetic experiments were designed to test whether a direct interaction between Spir and Capu is required during oogenesis. Indeed, data in this study indicate that Spir and Capu must interact directly with one another and then separate to function properly. Furthermore, these actin regulators are controlled by a combination of mechanisms, including interaction with one another, functional inhibition and regulation of their protein levels. Finally, this work demonstrates for the first time in a multicellular organism that the ability of a formin to assemble actin filaments is required for a specific structure.
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Spire-Type Actin Nucleators Cooperate with Formin-2 to Drive Asymmetric Oocyte Division. Pfender S et al. 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.