To establish in vivo gonadal tumor models and permanent lines of gonadal somatic cells we produced transgenic (TG) mice expressing the Simian virus (SV) 40 T-antigens (T-ag), driven by 6 or 2.1 kilobase fragments of the mouse inhibin alpha-subunit promoter. Hitherto, altogether 44 TG mice, one of which carried the shorter transgene, have produced gonadal tumors. Two founder females expressing the longer transgene, KK1 and KK3, and three established TG mouse lines were studied in detail. Penetrance of the phenotype in IT6-M and IT6-F mouse lines was 100% (tumors/TG: IT6-M 22/22, IT6-F 14/14). The T-ag mRNA was strongly expressed in the gonads, adrenal glands, pituitary, and brain. The KK-1 and KK-3 ovarian tumor cells immunostained with anti-SV40 large-T antibody. The KK-1 cells possessed high-affinity LH receptors [equilibrium association constant (Ka = 7.8 x 10(10) liters/mol] and responded to human CG by elevated cAMP and progesterone production. Also FSH slightly stimulated their cAMP and estradiol production (P < 0.01). These cells expressed cytochrome P450arom and inhibin alpha mRNA, but not cytochrome P450c17 alpha. In conclusion, the KK-1 cells are immortalized luteinizing granulosa cells expressing endogenous gonadotropin receptors, steroidogenic enzymes, and inhibin alpha. These cells will be useful in studies on the molecular aspects of granulosa cell function. The present study indicates that the 6-kilobase fragment of the inhibin alpha promoter described in this article contains the elements directing tissue-specific expression in vivo and is useful for targeted expression of other genes in the gonads.