Analyses of raf family gene expression in tissues from a variety of organisms have established that these genes are regulated at the level of transcription or post-transcriptional processing by developmental, tissue-specific, and tumor-specific factors. Transcripts of raf-1 are ubiquitously expressed, whereas A-raf and B-raf transcripts are predominantly expressed in urogenital tissues and brain, respectively. The A-raf promoter region has a low GC-content (40%), unlike the raf-1 promoter region (60%), and contains multiple potential response elements for regulatory transcription factors including Ets, interferon-stimulated gene factor-2, and steroid hormone receptors. Since urogenital tissues are responsive to steroid hormones, we examined dexamethasone regulation of A-raf promoter activity and found that the glucocorticoid receptor specifically interacts with the A-raf promoter in vitro and induces the A-raf promotor activity in vivo. Since earlier attempts at generating transgenic mice carrying 3611-murine sarcoma virus were unsuccessful, oncogenically activated and wild-type versions of raf-1 under the transcriptional control of the raf-1, A-raf, or cytomegalovirus promoters were microinjected into mouse zygotes and implanted into pseudopregnant females. Founder mice were obtained expressing normal but not oncogenic raf from the raf-1 promoter, indicating that under these conditions oncogenic versions of raf are embryonic lethals and that the raf-1 promoter is position independent. However, using an oncogenic version of raf-1 under the transcriptional control of the A-raf promoter region (pARP1BXB), three founder mice were identified bearing one to two copies of the transgene. In the F3 generation, pARP1BXB mice displayed bilateral and unilateral eye abnormalities (cataracts and microphthalmias), hydrocephalies, and preliminary necropsy results showed multiple kidney cysts with areas of hyperplasia, thymic and/or splenic foci, and coagulating gland hyperplasia. These studies demonstrate that oncogenic versions of raf family proto-oncogenes can be passed through the mouse germ line and cause developmental anomalies and preneoplastic lesions.
