The exoribonuclease Xrn1 is widely recognised as a key component in the 5'-3' 
RNA degradation pathway. This enzyme is highly conserved between yeast and 
humans and is known to be involved in RNA interference and degradation of 
microRNAs as well as RNA turnover. In yeast and human tissue culture cells, Xrn1 
has been shown to be a component of P-bodies (processing bodies), dynamic 
cytoplasmic granules where RNA degradation can take place. In this paper we show 
for the first time that Pacman, the Drosophila homologue of Xrn1, is localized 
in cytoplasmic particles in Drosophila testis cells. These particles are present 
in both the mitotically dividing spermatogonia derived from primordial stem 
cells and in the transcriptionally active spermatocytes. Pacman is co-localized 
with the decapping activator dDcp1 and the helicase Me31B (a Dhh1 homologue) in 
these particles, although this co-localization is not completely overlapping, 
suggesting that there are different compartments within these granules. 
Particles containing Pacman respond to stress and depletion of 5'-3' decay 
factors in the same way as yeast P-bodies, and therefore are likely to be sites 
of mRNA degradation or storage. Pacman is shown to be required for normal 
Drosophila spermatogenesis, suggesting that control of mRNA stability is crucial 
in the testis differentiation pathway.