No abstract

Expression of the int-3 locus is activated in mouse mammary tumors as a consequence of insertional mutagenesis by the mouse mammary tumor virus (MMTV). Integration of the MMTV pro virus into the int-3 locus promotes the transcription and translation of flanking cellular int-3 sequences sharing significant homology with the intracellular domain of the neurogenic Notch gene of Drosophila, and with the yeast cell cycle regulatory genes cdclO and SWI6. To determine the in vivo consequences of activated int-3 expression, transgenic mice were generated harboring a genomic tumor DNA fragment consisting of the MMTV LTR and the flanking cellular int-3 sequences. All six int-3 founder transgenic mice and the progeny of one established line exhibited similar dramatic phenotypic abnormalities in tissues in which the transgene was expressed. Focal and often multiple poorly differentiated mammary and salivary adenocarcinomas appeared in the majority of transgenic mice between 2 and 7 months of age. Significantly, mammary glands were arrested in development and were lactation deficient in all female int-3 mice. The salivary glands, glands of the nasal mucosa and maxillary sinus, the extraorbital lacrimal glands, and the Harderian glands of juvenile and adult transgenic mice all contained proliferating immature ductule cells and were incompletely differentiated. In addition, all male int-3 transgenic mice were sterile, apparently the result of severe hyperplasia of the epididymis. These findings demonstrate in vivo that expression of the activated NotcA-related int-3 gene causes deregulation of normal developmental controls and hyperproliferation of glandular epithelia.

Transgenic mice were generated with a human epidermal growth factor (EGF) receptor cDNA driven by the chicken 13-actin gene promoter. One line (AE24) that exhibited a unique expression pattern in which dramatically elevated levels of EGF receptor RNA were found only in the testis was established, suggesting that the 13-actin promoter was being influenced by an adjacent testis-specific enhancer. EGF receptor RNA was detected in primary spermatocytes, whereas the synthesis of receptor protein was restricted to elongate spermatids, indicating that transgene expression was under translational control. At spermiation, the EGF receptor was sequestered in residual bodies and excluded from mature sperm by a compartmentalization mechanism. About half of AE24 homozygous males were sterile because of sperm paralysis, whereas heterozygous males and females of either genotype were completely fertile. Electron microscopic analysis of sperm flagella from sterile AE24 homozygotes revealed an aberrant axonemal structure in which outer doublet microtubules were missing from the middle piece, resembling changes observed in the sperm of some infertile humans. Flagellar axonemal disassembly was observed in the vas deferens and epididymis but not in the testis, suggesting that outer doublets were assembled in a grossly normal manner but possessed a latent instability. These results demonstrate that in the AE24 mouse line the EGF receptor transgene was integrated into and inactivated an endogenous autosomal gene, causing sperm flagellar axonemal disruption and male sterility.

Many human cancers that are initially responsive to chemotherapy eventually fail to respond to treatment. For some drugs, dose escalation that may be required for a cure cannot be achieved because sensitive tissues such as bone marrow (BM) limit cytotoxic therapy. Approaches to prevent or circumvent BM toxicity are therefore a high priority of research on dose escalation protocols. In this study, we have transplanted BM cells from transgenic mice that constitutively express physiologic amounts of a functional human multidrug resistance (MDR1) cDNA to lethally irradiated C57BL/6 x SJL F1 mice (n = 36). From 6 weeks to 10 months after the transplant, all animals contained MDR1 DNA in spleen and BM specimens as indicated by Southern blot analysis, and expressed MDR1 messenger RNA in BM samples as detected by slot blot analysis. In addition, these animals were resistant to the myelosuppressive effect of doxorubicin, daunomycin, taxol, vinblastine, vincristine, etoposide, and actinomycin D, whereas control animals that were reconstituted with normal BM were drug sensitive. Finally, the chemoprotection afforded by the MDR1 gene could readily be reversed by adding chemosensitizers such as cyclosporin A and R-verapamil to chemotherapy. Hence, it appears that BM cells expressing the human MDR1 gene maintain this function after transplantation to host animals for a minimum of 10 months, and confer multidrug resistance to these BM recipients. This selective advantage conferred by expression of the MDR1 cDNA suggests a strategy for the use of MDR1 gene therapy in cancer chemotherapy and for the introduction of otherwise nonselectable genes into BM.