Expression of a mouse Zfy-1/lacZ transgene in the somatic cells of the embryonic gonad and germ cells of the adult testis.

The Zfy-1 and Zfy-2 genes, which arose by gene duplication, map to the mouse Y chromosome and encode nearly identical zinc-finger proteins. Zfy-1 is expressed in the genital ridge and adult testis and likely encodes a transcription activator. Although potential roles in sex determination and spermatogenesis have been hotly debated, the biological functions of Zfy-1 remain unknown. To study the gene's regulation, transgenes with 21-28 kb of Zfy-1 5' flanking DNA placed upstream of lacZ were constructed in plasmids or created by homologous recombination of coinjected DNA molecules. The resulting transgenic mice expressed beta-galactosidase in the genital ridge of both males and females starting between embryonic day 10 and 11 (E10-E11), peaking at E12-E13 and then declining to low levels by E15, a pattern that matches Zfy-1 mRNA as detected by RT-PCR. This lacZ expression in genital ridge was confined to somatic cells as demonstrated by its absence from the alkaline phosphatase-positive germ cells. It had been reported previously that Zfy-1 mRNA was absent from the embryonic gonad of homozygous W(e) embryos, which virtually lack germ cells. By contrast, we observed normal expression of the Zfy-1/lacZ transgene when introduced into the W(e) background, suggesting that germ cells are not necessary for expression. In the adult, the Zfy-1/lacZ transgene is expressed abundantly in developing germ cells. Extragonadal (kidney, meninges, arteries, choroid plexus) expression of the transgene was also observed in embryos. A smaller transgene with only 4.3 kb of Zfy-1 5' flanking DNA was expressed only in germ cells of adult mice. These results suggest that an enhancer for germ cell expression in the adult lies near the Zfy-1 promoter and that an enhancer for expression in the somatic cells of the embryonic gonad is located further 5'.