Asterless Licenses Daughter Centrioles to Duplicate for the First Time in Drosophila Embryos

Abstract

SummaryCentrioles form centrosomes and cilia, and defects in any of these three organelles are associated with human disease [1]. Centrioles duplicate once per cell cycle, when a mother centriole assembles an adjacent daughter during S phase. Daughter centrioles cannot support the assembly of another daughter until they mature into mothers during the next cell cycle [2–5]. The molecular nature of this daughter-to-mother transition remains mysterious. Pioneering studies in C. elegans identified a set of core proteins essential for centriole duplication [6–12], and a similar set have now been identified in other species [10, 13–18]. The protein kinase ZYG-1/Sak/Plk4 recruits the inner centriole cartwheel components SAS-6 and SAS-5/Ana2/STIL, which then recruit SAS-4/CPAP, which in turn helps assemble the outer centriole microtubules [19, 20]. In flies and humans, the Asterless/Cep152 protein interacts with Sak/Plk4 and Sas-4/CPAP and is required for centriole duplication, although its precise role in the assembly pathway is unclear [21–24]. Here, we show that Asl is not incorporated into daughter centrioles as they assemble during S phase but is only incorporated once mother and daughter separate at the end of mitosis. The initial incorporation of Asterless (Asl) is irreversible, requires DSas-4, and, crucially, is essential for daughter centrioles to mature into mothers that can support centriole duplication. We therefore propose a “dual-licensing” model of centriole duplication, in which Asl incorporation provides a permanent primary license to allow new centrioles to duplicate for the first time, while centriole disengagement provides a reduplication license to allow mother centrioles to duplicate again.

Imaging cellular structures in super-resolution with SIM, STED and Localisation Microscopy: A practical comparison

“…We visualised them using Asterless (Asl), a component of the Drosophila centriole wall2930 and performed two measurements for each imaging technique: 1) the barrel width (N = 30), and 2) the FWHM of the Asl localisation signal in the centriole wall (N = 60) (Fig. 2).…”

The Centrosome and Its Duplication Cycle

“…In these experiments, disengaged centrioles could duplicate during the first interphase of a cycling extract, whereas engaged centrioles required an extra cycle to become disengaged. It has been suggested that recruitment of Asl onto the daughter centriole in Drosophila embryos occurs only once mother and daughter have separated at the end of mitosis and that this provides a duplication license (Novak et al 2014). However, it is notable that in cultured cells, the incorporation of Ana2 and Sas-6 onto the daughter's procentriole once it has disengaged from the mother in telophase appears to mark the very first event in the duplication process (Dzhindzhev et al 2014).…”

Once and only once: mechanisms of centriole duplication and their deregulation in disease

“…In both Drosophila and mammalian cells, PLK1 then triggers the sequential assembly of CEP135, CEP295/Ana1 and CEP152/Asl and downstream PCM formation 58,89,90 . Importantly, recruitment of Asl in Drosophila embryos only occurs after disengagement, indicating that these licensing processes occur sequentially 93 . In mammalian cells, CEP295 directly binds to CEP192 and contributes to the stabilization of centrioles after the loss of the cartwheel upon mitotic exit 89,94 .…”