AUTHOR=Lim Lin-Xenia , Isshiki Wakana , Iki Taichiro , Kawaguchi Shinichi , Kai Toshie 

TITLE=The Tudor Domain-Containing Protein, Kotsubu (CG9925), Localizes to the Nuage and Functions in piRNA Biogenesis in D. melanogaster

JOURNAL=Frontiers in Molecular Biosciences

VOLUME=Volume 9 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/molecular-biosciences/articles/10.3389/fmolb.2022.818302

DOI=10.3389/fmolb.2022.818302

ISSN=2296-889X

ABSTRACT=Silencing of transposable elements (TEs) by Piwi-interacting RNAs (piRNAs) is crucial for
maintaining germline genome integrity and fertility in animals. To repress TEs, PIWI-clade 
Argonaute proteins cooperate with Tudor domain-containing proteins at membraneless 
perinuclear organelles, called nuage, producing piRNAs to repress transposons. Here, we 
identify and characterize one of the Drosophila Tdrd1 orthologues, Kotsubu (Kots), which is a 
Tudor domain-containing protein encoded by CG9925 whose protein localizes to the nuage in 
gonads. We further show the dynamic localization of Kots in the male germline, where it shows
perinuclear signals in spermatogonia but forms large cytoplasmic condensates in the 
spermatocytes that overlap with piNG-body components, a nuage-associated organelle. The 
loss of kots resulted in a notable upregulation of stellate and a corresponding reduction in the 
Suppressor of Stellate piRNAs in the mutants. Furthermore, a moderate yet significant 
reduction of other piRNAs was observed in kots mutant testes, albeit to a weaker extent in 
mutant ovaries. Taken together, we propose that Kots functions in the piRNA pathway, 
predominantly in the male germline by forming discrete cytoplasmic granules.