Topaz1 (Testis and Ovary-specific PAZ domain gene 1) is a germ cell specific 
gene highly conserved in vertebrates. The putative protein TOPAZ1 contains a PAZ 
domain, specifically found in PIWI, Argonaute and Zwille proteins. Consequently, 
Topaz1 is supposed to have a role during gametogenesis and may be involved in 
the piRNA pathway and contribute to silencing of transposable elements and 
maintenance of genome integrity. Here we report Topaz1 inactivation in mouse. 
Female fertility was not affected, but male sterility appeared exclusively in 
homozygous mutants in accordance with the high expression of Topaz1 in male germ 
cells. Pachytene Topaz1--deficient spermatocytes progress through meiosis 
without either derepression of retrotransposons or MSCI dysfunction, but become 
arrested before the post-meiotic round spermatid stage with extensive apoptosis. 
Consequently, an absence of spermatids and spermatozoa was observed in 
Topaz1(-/-) testis. Histological analysis also revealed that disturbances of 
spermatogenesis take place between post natal days 15 and 20, during the first 
wave of male meiosis and before the generation of haploid germ cells. 
Transcriptomic analysis at these two stages showed that TOPAZ1 influences the 
expression of one hundred transcripts, most of which are up-regulated in mutant 
testis at post natal day 20. Our results also showed that 10% of these 
transcripts are long non-coding RNA. This suggests that a highly regulated 
balance of lncRNAs seems to be essential during spermatogenesis for induction of 
appropriate male gamete production.