Specialisation of ribosomes in gonads through paralog-switching

Ribosomes have long been thought of as homogeneous, macromolecular machines but recent evidence suggests they are heterogeneous and their specialisation can regulate translation. Here, we have characterised ribosomal protein heterogeneity across 5 tissues of Drosophila melanogaster. We find that testis and ovary contain the most heterogeneous ribosome populations, and that specialisation in these tissues occurs through paralog-switching. For the first time, we have solved structures of ribosomes purified from in vivo tissues by cryo-EM, revealing differences in precise ribosomal arrangement for testis and ovary 80S ribosomes. Differences in the amino acid composition of paralog pairs and their localisation on the ribosome exterior indicate paralog-switching could alter the ribosome surface, enabling different proteins to regulate translation. One testis-specific paralog-switching pair is also found in humans, suggesting this is a conserved site of ribosome specialisation. Overall, this work allows us to propose possible mechanisms by which ribosome specialisation can regulate translation.