Plays an important role in the organization of the cytoskeleton by regulating actin polymerization in two ways. Firstly, by binding to and sequestering actin monomers (G actin) inhibits actin polymerization. Secondly, by binding directly filamentous actin (F actin) promotes actin polymerization. Regulates the formation of cortical actin in oocytes conferring them enough rigidity to sustain the contractions during ovulation. Interacts (via repeats 1, 2 and 4) with G-actin in a 1:3 ratio. Interacts (via repeats 2 and 3) with F-actin. Localizes to the cell cortex and the cytoplasm in oocytes and at the inside edges of membrane cubicles surrounding germ cell nuclei. Co-localizes with actin at the cell-cell contact in two-cell stage embryo. At the comma stage, enriched in the developing nerve ring (at protein level). Ubiquitously expressed in larvae and adults with enrichment in the spermatheca, the intestinal tract and the posterior bulb of the pharynx (at protein level). Expressed in oocytes and in the gonad (at protein level). Expressed in embryo, larvae and adults (at protein level). The 4 repeats act cooperatively in the binding of G actin. Lethal at the L3/L4 larval stages or at the young adult stage. Mutants are shorter and stouter, and fail to produce a viable progeny. In oocytes, actin is diffused in the cytoplasm and F-actin accumulation at the cell cortex is reduced resulting in deformed oocytes in the spermatheca and the uterus. Belongs to the thymosin beta family.