We are exploring a new code for gene regulation at the level of ribosomes—the cell’s protein-making machinery—in guiding development of specific cells and tissue within an embryo. For every gene that becomes active, the information contained in its DNA is converted into a molecule of RNA, which is then “read” by ribosomes to make the proper protein. Within a given organism, scientists assumed that all ribosomes were essentially the same and that they exert largely rote-like functions, but I have discovered that ribosomes in different embryonic cells and tissues include distinct components and, as a result, are specialized for producing particular proteins. Now, my laboratory will delineate the differences in ribosome composition and activity in the various tissues of the developing mouse embryo. We will also investigate how these “specialized ribosomes” select which RNAs they will translate into proteins, by defining the sequences and/or structures within RNAs that interact with ribosome components. This work will reveal the role that ribosomes play in decoding how the genome is expressed in time and space during development, and could shed light on birth defects and human disease that are associated with mutations in ribosomal components.