BACKGROUND: We had previously reported that the Suppression Subtractive 
Hybridization (SSH) approach was relevant for the isolation of new mammalian 
genes involved in oogenesis and early follicle development. Some of these 
transcripts might be potential new oocyte and granulosa cell markers. We have 
now characterized one of them, named TOPAZ1 for the Testis and Ovary-specific 
PAZ domain gene.
PRINCIPAL FINDINGS: Sheep and mouse TOPAZ1 mRNA have 4,803 bp and 4,962 bp open 
reading frames (20 exons), respectively, and encode putative TOPAZ1 proteins 
containing 1,600 and 1653 amino acids. They possess PAZ and CCCH domains. In 
sheep, TOPAZ1 mRNA is preferentially expressed in females during fetal life with 
a peak during prophase I of meiosis, and in males during adulthood. In the 
mouse, Topaz1 is a germ cell-specific gene. TOPAZ1 protein is highly conserved 
in vertebrates and specifically expressed in mouse and sheep gonads. It is 
localized in the cytoplasm of germ cells from the sheep fetal ovary and mouse 
adult testis.
CONCLUSIONS: We have identified a novel PAZ-domain protein that is abundantly 
expressed in the gonads during germ cell meiosis. The expression pattern of 
TOPAZ1, and its high degree of conservation, suggests that it may play an 
important role in germ cell development. Further characterization of TOPAZ1 may 
elucidate the mechanisms involved in gametogenesis, and particularly in the RNA 
silencing process in the germ line.