RNA-binding protein required for embryonic and postnatal development of muscle tissue. May regulate intracellular transport and local translation of certain mRNAs (By similarity). Interacts with FMR1. Interacts with FRX2. Interacts with TDRD3. Interacts with HABP4. Interacts with CYFIP2 but not with CYFIP1. The tandem Agenet-like domains preferentially recognize trimethylated histone peptides. This protein corresponds to isoform B in mouse and isoform 2 in human. Belongs to the FMR1 family.