198
piRNA enzymes and function in piRNA biogenesis, as has also been shown for the
Vasa protein (Xiol et al. 2014 ).
Nuage and perinuclear granules process piRNAs and contain both piRNA core
enzymes like Miwi/Ziwi and Mili/Zili, as well as RNA-binding proteins like Vasa.
Importantly, they also contain scaffold proteins that bind and connect the RNA-
binding proteins with other RNA-binding proteins and with the piRNA enzymes
(Findley et al. 2003 ; Huang et al. 2011 ; Ma et al. 2009 ). In the absence of these
scaffolds, the nuage granules fall apart and the piRNA pathway is impaired (Findley
et al. 2003 ; Huang et al. 2011 ; Ma et al. 2009 ). One such scaffold protein in the
mouse nuage is the GasZ protein (Lim et al. 2013 ; Ma et al. 2009 ). GasZ is intrigu-
ingly detected in the Bb of zebrafish and Xenopus oocytes (Marlow and Mullins
2008 ; Yan et al. 2004 ). It was recently shown that the perinuclear piRNA pathway
granules also polarize and transition from being radially distributed in oogonia to
being localized to the cytoplasm apposing the bouquet telomere cluster, along with
the Bb precursor components (Elkouby et al. 2016 ). This included localization of
Vasa, Zili, Ziwi, and GasZ. It is possible that perinuclear granule components con-
tribute to the Bb, such as GasZ, or alternatively that GasZ has multiple distinct func-
tions in piRNA biogenesis and in the Bb, such as structurally maintaining these
granules as a scaffolding protein.
Acknowledgments We would like to acknowledge grants from the National Institutes of Health
R01GM056326 and R01GM117981 to M.C.M. and “BECAS CHILE DE DOCTORADO EN EL
EXTRANJERO” to M.E.A.
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