The inheritance of the centrosome during human fertilization remains mysterious. Here we show that the sperm centrosome contains, in addition to the known typical barrel-shaped centriole (the proximal centriole, PC), a surrounding matrix (pericentriolar material, PCM), and an atypical centriole (distal centriole, DC) composed of splayed microtubules surrounding previously undescribed rods of centriole luminal proteins. The sperm centrosome is remodeled by both reduction and enrichment of specific proteins and the formation of these rods during spermatogenesis. In vivo and in vitro investigations show that the flagellum-attached, atypical DC is capable of recruiting PCM, forming a daughter centriole, and localizing to the spindle pole during mitosis. Altogether, we show that the DC is compositionally and structurally remodeled into an atypical centriole, which functions as the zygote’s second centriole. These findings now provide novel avenues for diagnostics and therapeutic strategies for male infertility, and insights into early embryo developmental defects.

Reproductive success depends on efficient sperm movement driven by axonemal dynein-mediated microtubule sliding. Models predict sliding at the base of the tail – the centriole – but such sliding has never been observed. Centrioles are ancient organelles with a conserved architecture; their rigidity is thought to restrict microtubule sliding. Here, we show that, in mammalian sperm, the atypical distal centriole (DC) and its surrounding atypical pericentriolar matrix form a dynamic basal complex (DBC) that facilitates a cascade of internal sliding deformations, coupling tail beating with asymmetric head kinking. During asymmetric tail beating, the DC’s right side and its surroundings slide ~300 nm rostrally relative to the left side. The deformation throughout the DBC is transmitted to the head-tail junction; thus, the head tilts to the left, generating a kinking motion. These findings suggest that the DBC evolved as a dynamic linker coupling sperm head and tail into a single self-coordinated system.

Insects and mammals have atypical centrioles in their sperm. However, it is unclear how these atypical centrioles form. Drosophila melanogaster sperm has one typical centriole called the giant centriole (GC) and one atypical centriole called the proximal centriole-like structure (PCL). During early sperm development, centriole duplication factors such as Ana2 and Sas-6 are recruited to the GC base to initiate PCL formation. The centriolar protein, Poc1B, is also recruited at this initiation stage, but its precise role during PCL formation is unclear. Here, we show that Poc1B recruitment was dependent on Sas-6, that Poc1B had effects on cellular and PCL Sas-6, and that Poc1B and Sas-6 were colocalized in the PCL/centriole core. These findings suggest that Sas-6 and Poc1B interact during PCL formation. Co-overexpression of Ana2 and Sas-6 induced the formation of ectopic particles that contained endogenous Poc1 proteins and were composed of PCL-like structures. These structures were disrupted in Poc1 mutant flies, suggesting that Poc1 proteins stabilize the PCL-like structures. Lastly, Poc1B and Sas-6 co-overexpression also induced the formation of PCL-like structures, suggesting that they can function together during the formation of the PCL. Overall, our findings suggest that Poc1B and Sas-6 function together during PCL formation.

Reproductive success depends on efficient sperm movement driven by dynein-mediated microtubule sliding in the axoneme 1-3. Models predict sliding at the base of the tail – the centriole – but such sliding has never been observed 4,5. Centrioles are evolutionarily-ancient organelles with a conserved architecture 6-8, and their rigidity is thought to restrict microtubule sliding 1. Here, we show that, in mammalian sperm, the atypical distal centriole (DC) and its surrounding atypical pericentriolar matrix 9,10 form a dynamic basal complex (DBC) that facilitates a cascade of internal sliding deformations, coupling tail beating with asymmetric head kinking. During asymmetric tail beating, the DC’s right side and its surroundings slide ~300 nm rostrally relative to the left side. This deformation is transmitted through the DBC to the head-tail junction; as a result, the head tilts to the left, generating a kinking motion. These findings suggest that the DBC evolved to act as a mechanotransducer, coupling sperm head and tail into a single self-coordinated system. The DBC may act as a morphological computer 11, regulating tail beating from external feedback imparted to the head during sperm navigation. We anticipate our findings will enable studies of coordinated motion in sperm and cilia in many contexts.

In the original version of this Article, the affiliation details for Jadranka Loncarek and Vito Mennella were incorrectly given as ‘Cell Biology Program, The Hospital for Sick Children, Department of Biochemistry, University of Toronto, 555 University Avenue, Toronto, ON, M5G 1X8, Canada’ and ‘Laboratory of Protein Dynamics and Signaling, Center for Cancer Research, National Cancer Institute, 1050 Boyles Street, Frederick, MD, 21702, USA’, respectively. This has now been corrected in both the PDF and HTML versions of the Article.

No abstract

Centrioles are subcellular organelles with an evolutionarily conserved structure and a shock absorber-like function. In sperm, centrioles are found at the flagellum base and are essential for embryo development in basal animals. Yet, sperm centrioles have evolved diverse forms, sometimes acting like a transmission system, as in cattle, and sometimes becoming dispensable, as in house mice. How the essential sperm centriole evolved to become dispensable in some organisms is unclear. Here, we test the hypothesis that this transition occurred through a cascade of evolutionary changes to the proteins, structure, and function of sperm centrioles and was possibly driven by sperm competition. We found that the last steps in this cascade are associated with a change in the primary structure of the centriolar luminal protein FAM161A in rodents. This information provides the first insight into the molecular mechanisms and adaptive evolution underlying a major evolutionary transition within the internal structure of the mammalian sperm neck.

Reproductive success depends on efficient sperm movement driven by dynein-mediated microtubule sliding in the axoneme 1-3. Models predict sliding at the base of the tail – the centriole – but such sliding has never been observed 4,5. Centrioles are evolutionarily-ancient organelles with a conserved architecture 6-8, and their rigidity is thought to restrict microtubule sliding 1. Here, we show that, in mammalian sperm, the atypical distal centriole (DC) and its surrounding atypical pericentriolar matrix 9,10 form a dynamic basal complex (DBC) that facilitates a cascade of internal sliding deformations, coupling tail beating with asymmetric head kinking. During asymmetric tail beating, the DC’s right side and its surroundings slide ~300 nm rostrally relative to the left side. This deformation is transmitted through the DBC to the head-tail junction; as a result, the head tilts to the left, generating a kinking motion. These findings suggest that the DBC evolved to act as a mechanotransducer, coupling sperm head and tail into a single self-coordinated system. The DBC may act as a morphological computer 11, regulating tail beating from external feedback imparted to the head during sperm navigation. We anticipate our findings will enable studies of coordinated motion in sperm and cilia in many contexts.