Abstract
ABSTRACTCentrioles organise centrosomes and cilia, and these organelles have an important role in many cell processes. In flies, the centriole protein Ana1 is required for the assembly of functional centrosomes and cilia. It has recently been shown that Cep135 (also known as Bld10) initially recruits Ana1 to newly formed centrioles, and that Ana1 then recruits Asl (known as Cep152 in mammals) to promote the conversion of these centrioles into centrosomes. Here, we show that ana1 mutants lack detectable centrosomes in vivo, that Ana1 is irreversibly incorporated into centrioles during their assembly and appears to play a more important role in maintaining Asl at centrioles than in initially recruiting Asl to centrioles. Unexpectedly, we also find that Ana1 promotes centriole elongation in a dose-dependent manner: centrioles are shorter when Ana1 dosage is reduced and are longer when Ana1 is overexpressed. This latter function of Ana1 appears to be distinct from its role in centrosome and cilium function, as a GFP–Ana1 fusion lacking the N-terminal 639 amino acids of the protein can support centrosome assembly and cilium function but cannot promote centriole over-elongation when overexpressed.
Highlights
Centrioles are ancient cellular organelles that are required for the formation of centrosomes and cilia (Azimzadeh, 2014)
We found that ana1 mutants have a dramatic reduction in centrosome numbers in third-instar larval brains that is comparable to that observed in brains mutant for the essential centriole assembly genes Sas-4, Sas-6, ana2 and asl (Fig. 1A) (Basto et al, 2006; Baumbach et al, 2015; Cottee et al, 2015; Peel et al, 2007; Rodrigues-Martins et al, 2007)
Our results are consistent with recent reports that Ana1/Cep295 is required for centriole-to-centrosome conversion in flies and humans (Fu et al, 2016; Izquierdo et al, 2014), and we show that ana1 mutant cells have very few centrosomes in vivo
Summary
Centrioles are ancient cellular organelles that are required for the formation of centrosomes and cilia (Azimzadeh, 2014). Recent studies have revealed that only a relatively small number of proteins are essential for centriole assembly (Conduit et al, 2015a; Fırat-Karalar and Stearns, 2014; Gönczy, 2012; Jana et al, 2014) These proteins form a conserved pathway in which the protein kinase ZYG-1 (in worms), Plk (in mammals) or Sak (in flies) (Bettencourt-Dias et al, 2005; Delattre et al, 2006; Habedanck et al, 2005; Pelletier et al, 2006) recruits SAS-5/ Ana2/STIL (worms, flies and mammals, respectively) and Sas-6 to. Vertebrate cells appear to use a combination of these proteins (Cep192 and Cep152, respectively) (Kim et al, 2013; Park et al, 2014; Sonnen et al, 2013)
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