RNA-binding protein. Binds poly(G) and poly(U) but not poly(A) or poly(C). Regulates somite formation, probably by regulating gene expression. During embryogenesis, isoform 2 is present from fertilization (stage 0) whereas isoform 1 is first present after stage 30. In the tadpole (stage 36), isoform 1 shows high expression in somites forming the caudal muscle and low expression in the eye. In adults, isoform 1 is expressed in heart and muscle, whereas isoform 2 is expressed in the brain, liver and kidney. Belongs to the FMR1 family.