Summary
Transforming growth factor alpha (TGF-alpha) is a 50 amino acid secreted
polypeptide sharing 35% sequence homology with EGF. TGF-alpha binds to the EGF receptor
and like EGF, is a potent mitogen for several cell types. The EGF-like family of growth
factors and their receptors are prominantly associated with breast cancer. TGF-alpha
promotes proliferation and formation of lobuloalveolar structures in the normal mouse
mammary gland. Expression of TGF-alpha is found in up to 70% of human breast cancer biopsy
specimens and is thought to be important in early stages of mammary tumorigenesis. Because
TGF-alpha is a mitogen for mammary epithelium, it has been hypothesized to act as a tumor
promoter, increasing cell proliferation and providing an environment in which cancer is
more likely to result from background mutational events or carcinogenic initiators.
Citation
Matsui Y, Halter SA, Holt JT, Hogan BLM, Coffey RJ. 1990. Development of
mammary hyperplasia and neoplasia in MMTV-TGFalpha transgenic. Cell 61:1147-1155.
Background
Transgene
To construct pMMTV-TGFalpha, a pKCR vector in which the SV40 early promoter region was
replaced with complete MMTV LTR and a 925 bp human TGFA cDNA was inserted in the EcoRI
site of fl-globin exon 3. The 3.6 kb XhoI fragment was microinjected into (C57BL X DBA)F2
fertilized eggs. Transgenic mice are identified either by Southern blot using a fl-globin
exon 3 probe or by PCR.
mouse strain
The genetic background of this strain is inbred SJL. SJL/J mice may be used
as controls.
Mice are viable and fertile, although mice of the most extensively studied line lactate insufficiently to support the litter. Virgin transgenic mice show no mammary gland abnormalities prepubertally, but adult virgin mice have considerable alveolar gland hyperplasia. Pregnant transgenic mice show marked proliferation of the stromal cells, and alveolar secretion is markedly incresed compared to nontransgenic mice. After multiple pregnancies, isolated adenocarcinomas develop. No information was given on metastatic incidence. There is no apparent phenotypic effect in males. In females transgene expression was localized to the small ducts and alveoli in both virgin and pregnant mice as evidenced by in situ hybridization and by immunohistochemistry. Immunostaining also revealed some stromal staining in the hyperplastic areas. Egfr mRNA expression was also increased in mammary tissues expressing high levels of the transgene. Crosses between TGFA transgenic mice and TGFB1 transgenic mice demonstrate that these growth factors oppose each other's action on mammary gland development. The TGF-alpha transgenic mice would also be useful in crosses with mice carrying mutations in the EGF and EGFR families. The putative tumor-promoter effect of TGFA may also be useful in enhancing the detection of tumor-initiating events and in determining the actions of putative metastases- inducing genes.
Colony Maintenance
Transgenic lines were generated by mating founder animals to (C57BL X DBA/2)F1 males and
females. The strain is maintained by mating B6D2 F1 female by carrier male.
The genetic background of these strains is mixed C57BL/6 x DBA/2.
Mammary development
Mammary gland development was abnormal in the transgenic mice from the onset of puberty (earlier stages have not been examined). The reduced ductal development and branching, as well as the abnormal morphology of the ducts and TEB's, became quite pronounced by 10 weeks of age in the virgin female. The defects were not due to a delay of development, but were accompanied by morphogenetic defects in the ductal epithelia, particularly in the TEB's. Proliferation rates were similar in wild-type and transgenic glands, suggesting that another mechanism, such as apoptosis, is responsible for the reduced ductal development. Morphogenetic abnormalities persist into pregnancy and at parturition, but it is not clear if these defects are secondary, and due to the reduced ductal density.
Genetic Typing
Mechanistic implications
key words
mammary tumor, transgenic, TGFalpha, transforming growth factor alpha, MMTV, mouse mammary tumor virus
Dr. Robert Coffey
Vanderbilt University Medical Center
Department of Medicine
Division of Gastroenterology
Nashville, TN 37232
Phone 301-496-2433
FAX
e-mail Robert.James.Coffey@Vanderbilt.Edu
Jackson lab ID
B6D2-TgN(MMTVTGFA)29Rjc (JR# 2373)
Information submitted by
Debbie Krupke (dmk@jax.org)
Induced Mutant Resource
The Jackson Laboratory
For inquiries and to place a request for mice, contact the Customer Service Department at 1-800-422-MICE. B6D2-TgN(MMTVTGFA)254Rjc JR# 2459
contributed: March 1996
last update: December 1998