TISSUE-SPECIFIC EXPRESSION OF THE RAT ANDROGEN-BINDING PROTEIN SEX HORMONE-BINDING GLOBULIN GENE IN TRANSGENIC MICE

The testicular Sertoli cell produces an extracellular androgen-binding protein (ABP) that binds testosterone and dihydrotestosterone with hi gh affinity. The ABP gene also encodes plasma sex hormone-binding glob ulin (SHBG), which is produced by the liver of most species. Unlike th e human, adult rats and mice do not express SHBG. A 5.5-kb rat genomic DNA fragment was found to contain the entire coding region of ABP and 1.5 kb upstream of the transcription start site. To aid in identifica tion of the promoter and enhancer regions of the ABP/ SHBG gene, we de veloped transgenic mice that express the rat gene. The 5.5-kb DNA was microinjected into the pronuclei of fertilized mice ova, which were tr ansferred to the reproductive tract of pseudopregnant females. Three o f the offspring were identified as carriers of the rat gene by Souther n hybridization and these founders were bred with normal mice to estab lish heterozygous transgenic lines. Northern blot analysis, RNA-PCR an d sequencing of the PCR products from the adult transgenic mice reveal ed extremely high levels of the rat ABP mRNA in the testis, but no det ectable rat ABP mRNA in liver, kidney or brain. Primer extension exper iments showed that the correct transcript ion start site is utilized i n the transgenes. These data demonstrate that the 5.5-kb genomic DNA f ragment contains an element(s) capable of directing ABP gene expressio n in the testis. This enhancer should prove useful for the targeting o f specific gene products to the mature Sertoli cell in transgenic anim als.