Centriole duplication involves the growth of a procentriole next to the parental centriole. Mutations in STIL and CPAP/CENPJ cause primary microcephaly (MCPH). Here, we show that human STIL has an asymmetric localization to the daughter centriole and is required for procentriole formation. STIL levels oscillate during the cell cycle. Interestingly, STIL interacts directly with CPAP and forms a complex with hSAS6. A natural mutation of CPAP (E1235V) that causes MCPH in humans leads to significantly lower binding to STIL. Overexpression of STIL induced the formation of multiple procentrioles around the parental centriole. STIL depletion inhibited normal centriole duplication, Plk4-induced centriole amplification, and CPAP-induced centriole elongation, and resulted in a failure to localize hSAS6 and CPAP to the base of the nascent procentriole. Furthermore, hSAS6 depletion hindered STIL targeting to the procentriole, implying that STIL and hSAS6 are mutually dependent for their centriolar localization. Together, our results indicate that the two MCPH-associated proteins STIL and CPAP interact with each other and are required for procentriole formation, implying a central role of centriole biogenesis in MCPH.

Emerging evidence points towards an intricate relationship between the pandemic of coronavirus disease 2019 (COVID-19) and diabetes. While pre-existing diabetes is associated with severe COVID-19 , it is unclear if COVID-19 severity is a cause or consequence of diabetes . To mechanistically link COVID-19 to diabetes, we tested whether insulin-producing pancreatic β-cells can be infected by SARS-CoV-2 and cause β-cell depletion. We found that the SARS-CoV-2 receptor, ACE2 and related entry factors (TMPRSS2, NRP1, TRFC) are expressed in β-cells, with selectively high expression of NRP1. We discovered that SARS-CoV-2 infects human pancreatic β-cells in patients who succumbed to COVID-19 and selectively infects human islet β-cells in vitro . We demonstrated SARS-CoV-2 infection attenuates pancreatic insulin levels and secretion, and induces β-cell apoptosis, each rescued by NRP1 inhibition. Phosphoproteomic pathway analysis of infected islets indicates apoptotic β-cell signaling, similar to that observed in Type 1 diabetes (T1D). In summary, our study shows SARS-CoV-2 can directly induce β-cell killing.

Centrioles are cylindrical structures that are usually composed of nine triplets of microtubules (MTs) organized around a cartwheel-shaped structure. Recent studies have proposed a structural model of the SAS-6-based cartwheel, yet we do not know the molecular detail of how the cartwheel participates in centriolar MT assembly. In this study, we demonstrate that the human microcephaly protein, CEP135, directly interacts with hSAS-6 via its carboxyl-terminus and with MTs via its amino-terminus. Unexpectedly, CEP135 also interacts with another microcephaly protein CPAP via its amino terminal domain. Depletion of CEP135 not only perturbed the centriolar localization of CPAP, but also blocked CPAP-induced centriole elongation. Furthermore, CEP135 depletion led to abnormal centriole structures with altered numbers of MT triplets and shorter centrioles. Overexpression of a CEP135 mutant lacking the proper interaction with hSAS-6 had a dominantnegative effect on centriole assembly. We propose that CEP135 may serve as a linker protein that directly connects the central hub protein, hSAS-6, to the outer MTs, and suggest that this interaction stabilizes the proper cartwheel structure for further CPAP-mediated centriole elongation.

Primary cilia play essential roles in signal transduction and development. The docking of preciliary vesicles at the distal appendages of a mother centriole is an initial/critical step of ciliogenesis, but the mechanisms are unclear. Here, we demonstrate that myosin-Va mediates the transportation of preciliary vesicles to the mother centriole and reveal the underlying mechanism. We also show that the myosin-Va-mediated transportation of preciliary vesicles is the earliest event that defines the onset of ciliogenesis. Depletion of myosin-Va significantly inhibits the attachment of preciliary vesicles to the distal appendages of the mother centriole and decreases cilia assembly. Myosin-Va functions upstream of EHD1- and Rab11-mediated ciliary vesicle formation. Importantly, dynein mediates myosin-Va-associated preciliary vesicle transportation to the pericentrosomal region along microtubules, while myosin-Va mediates preciliary vesicle transportation from the pericentrosomal region to the distal appendages of the mother centriole via the Arp2/3-associated branched actin network.