TRiC Is a Structural Component of Mammalian Sperm Axonemes

The TRiC chaperonin is responsible for folding ~5%–10% of the proteome in eukaryotic cells. Our recent cryo-electron microscopy studies of axonemes from diverse mammalian cell types led to the surprising discovery that a fully assembled TRiC chaperonin is a structural component of mammalian sperm flagella, where it is tethered to the radial spokes of doublet microtubules. In contrast, axoneme-tethered TRiC is not observed in mammalian epithelial cilia, nor in any of the non-mammalian sperm flagella studied to date. In this Perspective, we explore several hypotheses for the potential functions of axoneme-tethered TRiC in mature sperm.