Targeting expression of a transforming growth factor beta 1 transgene to the pregnant mammary gland inhibits alveolar development and lactation.

Abstract

Transforming growth factor‐beta 1 (TGF‐beta 1) possesses highly potent, diverse and often opposing cell‐specific activities, and has been implicated in the regulation of a variety of physiologic and developmental processes. To determine the effects of in vivo overexpression of TGF‐beta 1 on mammary gland function, transgenic mice were generated harboring a fusion gene consisting of the porcine TGF‐beta 1 cDNA placed under the control of regulatory elements of the pregnancy‐responsive mouse whey‐acidic protein (WAP) gene. Females from two of four transgenic lines were unable to lactate due to inhibition of the formation of lobuloalveolar structures and suppression of production of endogenous milk protein. In contrast, ductal development of the mammary glands was not overtly impaired. There was a complete concordance in transgenic mice between manifestation of the lactation‐deficient phenotype and expression of RNA from the WAP/TGF‐beta 1 transgene, which was present at low levels in the virgin gland, but was greatly induced at mid‐pregnancy. TGF‐beta 1 was localized to numerous alveoli and to the periductal extracellular matrix in the mammary gland of transgenic females late in pregnancy by immunohistochemical analysis. Glands reconstituted from cultured transgenic mammary epithelial cells duplicated the inhibition of lobuloalveolar development observed in situ in the mammary glands of pregnant transgenic mice. Results from this transgenic model strongly support the hypothesis that TGF‐beta 1 plays an important in vivo role in regulating the development and function of the mammary gland.

Impairment of mammary lobular development induced by expression of TGF?1 under the control of WAP promoter does not suppress tumorigenesis in MMTV-infected transgenic mice

“…5 In neither WAP nor MMTV driven TGF␤1 transgenic animals, mammary carcinomas have been reported. 4,6 In particular, no mammary tumors were observed in 20 WAP-TGF␤1 females maintained as breeders in our colony for over 2 years. In this case, the average age of death was 22.0 months (Smith, unpublished data).…”

“…Figure 3 shows that tumors carried by transgenic (GR x FVB) as well as (Czech x FVB) mice showed the 2 porcine specific RNA species reported earlier in the WAP-TGF␤1 transgenic animals. 4 Northern blot analysis using a human TGF␤1 cDNA probe also showed the expression of the transgene in transgenic (BALB/c x FVB) mice (data not shown).…”

“…In this model no inhibition of mammary ductal growth at puberty was observed. 4 With the onset of pregnancy, lobule-alveolar growth and development were impaired to the extent that lactation was impossible. Subsequent transplantation studies demonstrated that this phenotype was intrinsic to the transgenic epithelium expressing WAPdriven TGF␤1 and that the effect was cis in nature, i.e., autocrine rather than paracrine.…”

“…W␤9 (WAP-TGF␤1) transgenic male mice that were generated in a FVB/N background, 4 were crossbred with GR, Czech and BALB/c females. The two former strains carried their own MMTV variants, whereas BALB/c mice carried either no exogenous MMTV, MMTV (C3H) or MMTV (BALB2, BALB 14 and LA) virus.…”

“…Twenty g of total RNA was separated electrophoretically in a 0.8% formaldehyde-agarose gel, and transferred to positively charged Nylon membranes (Ambion, Austin, TX). Expression of WAP-TGF␤1 transgene was determined with a porcine specific TGF␤1 probe, as described before 4 and with a human TGF␤1 cDNA probe. 17 WAP and ␤-casein probe preparation was also described elsewhere.…”