DEVELOPMENT OF NEUROEPITHELIAL TUMORS OF THE ADRENAL-MEDULLA IN TRANSGENIC MICE EXPRESSING A MOUSE HYPOTHALAMIC GROWTH HORMONE-RELEASING HORMONE PROMOTER-SIMIAN VIRUS-40 T-ANTIGEN FUSION GENE

Expression of the mouse OH-releasing hormone (GRH) gene is restricted to neurons within the hypothalamus and to placenta. In an attempt to g enerate immortalized mouse hypothalamic neurons expressing GRH, the pr oximal 872-nucleotide segment of the 5'-flanking region of the hypotha lamic mouse GRH gene was cloned by polymerase chain reaction and ligat ed to a 2.7-kilobase DNA sequence encoding the simian virus-40 (SV40) T-antigen, so that regulation of SV40 T-antigen expression was depende nt on sequences within the mGRH 5'-flanking region. This region contai ns both TATA and CAAT boxes. The mouse GRH/SV40 T-antigen fusion gene was injected into 1-cell mouse embryos, and SV40 T-antigen incorporati on in the mouse genome was found in 11 of 77 live births (3 males and 8 females). Although no evidence of hypothalamic tumors was found, all mice that expressed the transgene also developed tumors originating i n the adrenal medulla. Gene copy number varied from 1-20 and was inver sely proportional to survival, which ranged from 7-16 weeks. Corticost erone levels were normal. The male transgenic mice were fertile, and t heir progeny expressed the transgene and developed similar tumors. Mic roscopic examination of the tumors revealed a primitive neuroectoderma l neoplasm that exhibited hematogenous and lymph node metastases and c ontained 100 ng norepinephrine, 2.85 ng epinephrine, and 1.1 ng dopami ne/mg tumor tissue. Primary culture of dispersed tumor cells released norepinephrine into the medium (180 pg/ml.24 h). Cell lines from 2 tum ors were established and exhibited characteristics similar to those of mixed neuroblastoma or primitive neuroectodermal tumors. In conclusio n, the proximal 872 nucleotides of the hypothalamic mouse GRH promoter contain elements directing tissue-specific expression limited to earl y adrenal neuroectodermal cells. Other GRH DNA sequences appear to be required for restricted expression of mouse GRH within the hypothalamu s.