Actin-binding protein that is involved in actin cytoskeleton assembly and reorganization (PubMed:18848445, PubMed:21620703). Acts as an actin nucleation factor and promotes assembly of actin filaments together with SPIRE1 and SPIRE2 (PubMed:18848445, PubMed:21620703). Involved in intracellular vesicle transport along actin fibers, providing a novel link between actin cytoskeleton dynamics and intracellular transport (PubMed:21983562). Required for asymmetric spindle positioning, asymmetric oocyte division and polar body extrusion during female germ cell meiosis (PubMed:12447394, PubMed:18848445, PubMed:19062278, PubMed:21620703). Plays a role in responses to DNA damage, cellular stress and hypoxia by protecting CDKN1A against degradation, and thereby plays a role in stress-induced cell cycle arrest (By similarity). Also acts in the nucleus: together with SPIRE1 and SPIRE2, promotes assembly of nuclear actin filaments in response to DNA damage in order to facilitate movement of chromatin and repair factors after DNA damage (By similarity). Protects cells against apoptosis by protecting CDKN1A against degradation (By similarity). Interacts with SPIRE1 (PubMed:21705804). Binds actin (PubMed:21705804). Interacts with CDKN1A (By similarity). Colocalizes with the actin cytoskeleton (PubMed:21705804). Recruited to the membranes via its interaction with SPIRE1 (PubMed:21705804). Detected at the cleavage furrow during asymmetric oocyte division and polar body extrusion (PubMed:21620703). Accumulates in the nucleus following DNA damage (By similarity). Detected in brain and in oocytes (at protein level) (PubMed:12447394, PubMed:19062278). Expressed almost exclusively in the developing and mature central nervous system (PubMed:10781961). Detected in oocytes (PubMed:12447394, PubMed:19062278). Expression begins at embryonic day 9.5 in the developing spinal cord and brain structures and continues in neonatal and adult brain structures including the olfactory bulb, cortex, thalamus, hypothalamus, hippocampus and cerebellum. No visible phenotype in male mice, but female mice show reduced fertility and produce at most one to three pups per litter (PubMed:12447394). Female mice display defects in asymmetric spindle positioning, asymmetric cell division and polar body extrusion during oocyte meiosis (PubMed:12447394). During early pregnancy, females present normal numbers of implantation sites, but only very few normal-looking embryos (PubMed:12447394). Most of the embryos show developmental delays and gross morphological defects, leading to embryonic death (PubMed:12447394). Belongs to the formin homology family. Cappuccino subfamily.