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Comment |
Profilin 1 plays feedback role in actin-mediated polar body extrusion in mouse oocytes. Liu J et al. (2017) Mammalian oocytes undergo several crucial processes during meiosis maturation, including spindle formation and migration and polar body extrusion, which rely on the regulation of actin. As a small actin-binding protein, profilin 1 plays a central role in the regulation of actin assembly. However, the functions of profilin 1 in mammalian oocytes are uncertain. To investigate the function of profilin 1 in oocytes, immunofluorescent staining was first used to examine profilin 1 localisation. The results showed that profilin 1 was localised around the meiotic spindles and was colocalised with cytoplasmic actin. Knockdown (KD) of profilin 1 with specific morpholino microinjection resulted in failure of polar body extrusion. This failure resulted from an increase of actin polymerisation both at membranes and in the cytoplasm. Furthermore, western blot analysis revealed that the expression of Rho-associated kinase (ROCK) and phosphorylation levels of myosin light chain (MLC) were significantly altered after KD of profilin 1. Thus, the results indicate that a feedback mechanism between profilin, actin and ROCK-MLC2 regulates actin assembly during mouse oocyte maturation.//////////////////
Spire and formin 2 synergize and antagonize in regulating actin assembly in meiosis by a ping-pong mechanism. Montaville P 2014 et al.
In mammalian oocytes, three actin binding proteins, Formin 2 (Fmn2), Spire, and profilin, synergistically organize a dynamic cytoplasmic actin meshwork that mediates translocation of the spindle toward the cortex and is required for successful fertilization. Here we characterize Fmn2 and elucidate the molecular mechanism for this synergy, using bulk solution and individual filament kinetic measurements of actin assembly dynamics. We show that by capping filament barbed ends, Spire recruits Fmn2 and facilitates its association with barbed ends, followed by rapid processive assembly and release of Spire. In the presence of actin, profilin, Spire, and Fmn2, filaments display alternating phases of rapid processive assembly and arrested growth, driven by a 'ping-pong' mechanism, in which Spire and Fmn2 alternately kick off each other from the barbed ends. The results are validated by the effects of injection of Spire, Fmn2, and their interacting moieties in mouse oocytes. This original mechanism of regulation of a Rho-GTPase-independent formin, recruited by Spire at Rab11a-positive vesicles, supports a model for modulation of a dynamic actin-vesicle meshwork in the oocyte at the origin of asymmetric positioning of the meiotic spindle.
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