Androgen regulation and prostatic‐specific expression of targeted genes in transgenic mice can be controlled by a small DNA fragment of the probasin (PB) promoter (−426 +28 base pairs, bp). Although the small PB fragment was sufficient to direct prostate‐specific expression, the low levels of transgene expression suggested that important upstream regulatory sequences were missing.

To enhance transgene expression, a large fragment of the PB promoter (LPB, −11,500 to +28 bg) was isolated, linked to the bacterial chloramphenicol acetyl transferase (CAT) gene, and microinjected into CD1 mouse oocytes to generate transgenic mouse lines.

As shown by the immunohistochemical studies, CAT gene expression was restricted to the prostatic epithelial cells in a tissue‐specific manner. High levels of CAT gene expression were observed in two of the six LPB‐CAT transgenic lines. In Line I, developmental regulation of LPB‐CAT was detected early, from 1 to 4 weeks of age, with the activity of serum androgen levels (7 weeks of age), a further 18‐fold rise in CAT activity occurred. Hormone ablation by castration in mature mice dramatically reduced transgene expression, whereas treatment with glucocorticoids had no signifant effect on CAT gene expression. Zinc treatment of the castrated animals also increased LPB‐CAT expression three‐ to four‐fold in two prostatic lobes.

This study demonstrates that important regulatory DNA sequences located in the LPB fragment contribute to tissue‐specific and greatly increase levels of transgene expression induced by androgens and zinc. Prostate 32:129–139, 1997. © 1997 Wiley‐Liss, Inc.