Polyribosome-associated RNA-binding protein that plays a role in neuronal development and synaptic plasticity through the regulation of protein synthesis of mRNAs (PubMed:11046149, PubMed:11733059, PubMed:12368261, PubMed:17178403). Plays a role as a negative translational regulator of specific mRNAs (PubMed:11733059, PubMed:17178403). Represses translation of the microtubule-associated protein futsch mRNA to regulate microtubule-dependent synaptic growth and function (PubMed:11733059). Localizes to specific N6-methyladenosine (m6A)-containing RNAs as part of a complex with the m6A reader Ythdf and thereby regulates axonal growth in the mushroom bodies and neuromuscular junctions (PubMed:33428246). May also be involved in microRNA (miRNA)-mediated translational suppression as part of the RNA-induced silencing complex (RISC) (PubMed:12368261, PubMed:14508492). Required for stability of the central pair of microtubules in the spermatid axoneme (PubMed:15183715). Regulates photoreceptor structure and neuromuscular junction (NMJ) neurotransmission in the eye (PubMed:11733059, PubMed:17178403). During embryogenesis, involved in germline fate determination (PubMed:16949822). Homodimer (PubMed:11046149). Interacts with AGO2, Dcr-1, Rm62, vig, RpL5 and RpL11; these interactions form the RNA-induced silencing complex (RISC), a messenger ribonucleoprotein particle (RNP) complex involved in translation regulation (PubMed:12368261, PubMed:14508492). As part of the RISC complex, interacts with Tudor-SN (PubMed:14508492). Component of a neuronal RNP at least composed of Fmr1, tral and me31B (PubMed:17178403). Interacts with piwi and vas; these interactions occur in the polar granules (PubMed:16949822). Interacts with Sra-1 (PubMed:12818175). Associates with polyribosome (PubMed:12368261). Interacts with Ythdf; the interaction is RNA independent (PubMed:33428246). Localizes in the neuronal soma and cell processes, and in pre- and postsynaptic neurons, as well as in postsynaptic muscles. Highly expressed in testes in the early stages of spermatogenesis before spermatid individualization (at protein level) (PubMed:15183715). Expressed during the embryonic development (PubMed:11046149). Expressed both maternally and zygotically in embryos (PubMed:11046149). Until early gastrulation, expression is uniformly distributed in the embryo (PubMed:11046149). At mid-gastrulation (stage 11), expressed everywhere with discernible concentration in the mesoderm (PubMed:11046149). After gastrulation (stage 14), expressed in the mesoderm, ventral nerve cord, and brain (PubMed:11046149). At stage 16, elevated expression is also seen in the muscle (PubMed:11046149). Highly expressed in nervous system throughout later development (at protein level) (PubMed:11046149, PubMed:11733059). Belongs to the FMR1 family.