Mammary gland development is mediated by both stromal and epithelial progesterone receptors

A combination of a knockout mouse model, tissue transplantation, and gene expression analysis has been used to investigate the role of steroid hormones in mammary gland development. Mouse mammary gland development was examined in progesterone receptor knockout (PRKO) mice using reciprocal transplantation experiments to investigate the effects of the stromal and epithelial PRs on ductal and lobuloalveolar development. The absence of PR in transplanted donor epithelium, but not in recipient stroma, prevented normal lobuloalveolar development in response to estrogen (E) and progesterone (P) treatment. Conversely, the presence of PR in the transplanted donor epithelium, but not in the recipient stroma, revealed that PR in the stroma may be necessary for ductal development. Members of the Wnt growth factor family, Wnt-2 and Wnt-5B, were employed as molecular markers of steroid hormone action in the mammary gland stroma and epithelium, respectively, to investigate the systemic effects of E and P. Hormonal treatment of intact, ovariectomized, and PR-/- mice and mice after transplantation of PR-/- epithelium into wild type (PR+/+) stroma demonstrated that these two locally acting growth factors are regulated by independent mechanisms. Wnt-2 is acutely repressed by E alone, while Wnt-5B gene expression is induced only after chronic treatment with both E and P. Wnt 5B appears to be one of the few molecular markers of P action in the mammary epithelium. This study suggests that the regulation of mammary gland development by steroid hormones is mediated by distinct effects of the stromal and epithelial PR and differential growth factor expression.

The carboxy-terminal domain of human surfactant protein B is not required for secretion in milk of transgenic mice

Previous studies in which human pulmonary surfactant protein B (SP-B) was targeted to the mammary gland of transgenic mice using the rat whey acidic protein (WAP) regulatory sequences resulted in secretion of only the unprocessed proprotein (42 kDa) in milk. To test the feasibility of producing a partially processed SP-B protein in milk, a new construct was designed in which the coding region for the carboxy-terminal domain was deleted. Expression of rWAP/SP-BDELTA C mRNA was detected in all three transgenic lines generated, and the expected carboxy-terminal deleted SP-B molecule (28 kDa), identified by using domain-specific antibodies, was secreted in the milk. Histochemical examination of lactating mammary tissue from the transgenic line expressing the highest levels of WAP/SP-BDelta C mRNA revealed an inhibition of lobulo-alveolar development, and led to growth retardation in pups, apparently due to the decreased milk production. Mothers from this line tended to cannibalize litters in mid-lactation. This phenotype has been observed previously with several other WAP-based transgenes. This phenotype suggests that there may be an upper limit to the level of SP-BDeltAC which can be produced in milk

Nephelometer optical response model for the interpretation of atmospheric aerosol measurements

A numerical model evaluating the response of a typical integrating nephelometer is described. The model incorporates the actual scattering geometry as well as the effects of a finite light source, detector size, and a nonideal Lambertian diffuser. An angular scattering weighting function is introduced to provide a tractable approach in numerical calculations and easy application. Using established size distribution ensembles associated with a few representative aerosol types, we compare the calculated response of a real nephelometer with that of an ideal, or perfect, nephelometer. The results indicate that, frequently, the nephelometer-produced aerosol-scattering coefficient is of the order of 10-20% too small; but for some naturally occurring aerosols, the difference may be as large as 40-50%. For a multiple-wavelength nephelometer, the response model can be employed to estimate the expected error in the aerosol-scattering coefficients directly from the measurements themselves.

Secretion of unprocessed human surfactant protein B in milk of transgenic mice

Because of the apparent clinical importance of human pulmonary surfactant B (SP-B), the expression of SP-B was directed to the mammary gland of transgenic mice using previously characterized rat whey acidic protein (WAP) regulatory sequences. rWAP/SP-B mRNA was expressed specifically in the mammary gland, and ranged from 1 to 5% of the endogenous WAP mRNA levels. SP-B was detected immunologically in both tissue and milk. The transgene product had an apparent molecular weight of 40-45 kDa, corresponding to the predicted size of the SP-B proprotein. Incubation of an SP-B-enriched fraction of milk with cathepsin D in vitro produced 20-25 kDa species, consistent with cleavage of the amino terminal domain by cathepsin D. This was confirmed using antibodies specific to the carboxy-terminal domain of SP-B. However, the appearance of only the SP-B proprotein in milk suggests that cathepsin D is not involved in the in vivo processing of SP-B. The SP-B proprotein in milk suggests that cathepsin D is not involved in the in vivo processing of SP-B. The SP-B proprotein can be expressed in milk of transgenic mice without any observed effects on mammary gland morphology or lactation.

Medical electronic link (MEL): providing telemedicine on the World Wide Web

Many tertiary care centers in the USA have attempted to implement interactive television (IATV) or dynamic telemedicine systems. The advantage these systems provide is real-time interaction. The biggest disadvantage is cost: expensive hardware, band-width and personnel. An alternative to IATV is Medical Electronic Link (MEL); a low cost, store-forward, internet-based physician consultation system. MEL allows physicians in remote locations to consult physicians at the Dartmouth Hitchcock Medical Center in Lebanon, New Hampshire by using the World Wide Web. The Benefits of MEL are low hardware and band-width costs, accessibility, a self-explanatory interface, convenience, and its use of the case record. This system has been implemented at a family practice clinic in Manchester, NH and at the Tribhuvan University Teaching Hospital in Kathmandu, Nepal.

Apoptosis in the terminal endbud of the murine mammary gland: a mechanism of ductal morphogenesis

Ductal morphogenesis in the rodent mammary gland is characterized by the rapid penetration of the stromal fat pad by the highly proliferative terminal endbud and subsequent formation of an arborized pattern of ducts. The role of apoptosis in ductal morphogenesis of the murine mammary gland and its potential regulatory mechanisms was investigated in this study. Significant apoptosis was observed in the body cells of the terminal endbud during the early stage of mammary ductal development. Apoptosis occurred predominately in defined zones of the terminal endbud; 14.5% of the cells within three cell layers of the lumen were undergoing apoptosis compared to 7.9% outside this boundary. Interestingly, DNA synthesis in the terminal endbud demonstrated a reciprocal pattern; 21.1% outside three cell layers and 13.8% within. Apoptosis was very low in the highly proliferative cap cell laver and in regions of active proliferation within the terminal endbud. In comparison to other stages of murine mammary gland development, the terminal endbud possesses the highest level of programmed cell death observed to date. These data suggest that apoptosis is an important mechanism in ductal morphogenesis. In p53-deficient mice, the level of apoptosis was reduced, but did not manifest a detectable change in ductal morphology, suggesting that p53-dependent apoptosis is not primarily involved in formation of the duct. Immunohistochemical examination of the expression of the apoptotic checkpoint proteins, Bcl-x, Bax and Bcl-2, demonstrated that they are expressed in the terminal endbud. Bcl-x and Bcl-2 expression is highest in the body cells and lowest in the nonapoptotic cap cells, implying that their expression is associated with increased apoptotic potential. Bax expression was distributed throughout the terminal endbud independent of the observed pattern of apoptosis. A functional role for Bcl-2 family members in regulating endbud apoptosis was demonstrated by the significantly reduced level of apoptosis observed in WAP-Bcl-2 transgenic mice. The pattern of apoptosis and ductal structure of endbuds in these mice was also disrupted. These data demonstrate that p53-independent apoptosis may play a critical role in the early development of the mammary gland.

Production of active bovine tracheal antimicrobial peptide in milk of transgenic mice

Tracheal antimicrobial peptide (TAP) is a member of the beta-defensin family of antibiotic peptides found in the tracheal mucosa of the cow. TAP gene expression in the bovine airway is inducible by lipopolysaccharide and inflammatory mediators, suggesting that it functions to protect the upper airway from infection. Limited availability of bovine TAP (bTAP) has precluded investigation of its potential utility in agriculture and medicine. To overcome this problem, transgenic mice expressing bTAP using an expression vector driven by control sequences from the murine whey acidic protein (WAP) gene have been generated. The WAP/bTAP transcript was detected in RNA isolated from mammary tissue of transgenic females. bTAP was purified to homogeneity from milk via acid precipitation, reverse-phase HPLC, and ion-exchange chromatography. This milk-derived bTAP had antimicrobial activity against Escherichia coli. Amino-terminal peptide sequencing confirmed the identity of this material as a bTAP isoform. bTAP available from a mammary gland bioreactor will allow evaluation of bTAP for use as an antibiotic in agriculture and medicine.

Expression of a translationally regulated, dominant-negative CCAAT/enhancer-binding protein beta isoform and up-regulation of the eukaryotic translation initiation factor 2alpha are correlated with neoplastic transformation of mammary epithelial cells

A translationally regulated, dominant-negative isoform of CCAAT/enhancer-binding protein beta is expressed in transplantable and primary mouse mammary tumors of different etiologies but is not expressed in preneoplastic mammary hyperplasias or in primary prostate, lung, lens, ovary or lymphoid tumors. The eukaryotic initiation factor 2alpha protein is also expressed at significantly higher levels (69.8 +/- 7.2%) in these mammary tumors compared with normal and hyperplastic tissues. Thus, misregulation of eukaryotic initiation factor 2alpha may promote the expression of a dominant-negative CCAAT/enhancer-binding protein beta isoform, which may inhibit terminal differentiation and facilitate uncontrolled proliferation of mammary epithelial cells.

Metastatic prostate cancer in a transgenic mouse

We have previously reported the development of a transgenic mouse model for prostate cancer derived from PB-Tag transgenic line 8247, henceforth designated the TRAMP (transgenic adenocarcinoma mouse prostate) model. We now describe the temporal and spatial consequences of transgene expression and report the identification and characterization of metastatic disease in the TRAMP model. TRAMP mice characteristically express the T antigen oncoprotein by 8 weeks of age and develop distinct pathology in the epithelium of the dorsolateral prostate by 10 weeks of age. Distant site metastases can be detected as early as 12 weeks of age. The common sites of metastases are the periaortic lymph nodes and lungs, with occasional metastases to the kidney, adrenal gland, and bone. By 28 weeks of age, 100% harbor metastatic prostate cancer in the lymph nodes or lungs. We have also demonstrated the loss of normal E-cadherin expression, as observed in human prostate cancer, as primary tumors become less differentiated and metastasize. The TRAMP model provides a consistent source of primary and metastatic tumors for histopathobiological and molecular analysis to further define the earliest molecular events involved in the genesis, progression, and metastasis of prostate cancer.

The mammary gland as a bioreactor: factors regulating the efficient expression of milk protein-based transgenes

Specific regulatory regions required for hormonal regulation and tissue-specific expression of rat beta-casein and why acidic protein (WAP) genes in the mammary gland have been defined. Composite response elements with multiple binding sites for several transcription factors have been identified. Mammary gland-specific gene expression appears not to be mediated by a single transcription factor, but instead requires cooperative interactions among several factors. Signal transduction pathways regulated by lactogenic hormones result in transcription factor binding and interaction within these elements, chromatin-structure changes, and milk-protein gene expression. Intragenic sequences in the 5' and 3' untranslated regions of the beta-casein and WAP mRNAs, respectively, also appear crucial for the efficient expression of these genes. Vectors to target the expression of heterologous genes, such as insulin-like growth factor I, to the mammary gland can be designed. This technology can be used to manipulate milk composition in transgenic animals, one result being improved infant formulas.

Targeted expression of des(1-3) human insulin-like growth factor I in transgenic mice influences mammary gland development and IGF-binding protein expression

To test the hypothesis that insulin-like growth factor I (IGF-I) regulates mammary gland development and lactation, the expression of both human (h) IGF-I and des(1-3)hIGF-I was targeted to the mammary gland in transgenic mice using a novel exon replacement strategy and the rat whey acidic protein (rWAP) gene regulatory sequences. Both transgenes expressed a 0.7-kilobase messenger RNA (mRNA). The abundance of WAP-IGE-I and WAP-DES mRNA on day 10 of lactation ranged from 0.2-1.0% and 0.2-13% of the endogenous mouse WAP mRNA, respectively. For WAP-DES mice, transgene expression was greatest from midpregnancy throughout lactation. Western blot analysis showed the presence of correctly processed hIGF-I in milk from these transgenic mice. This hIGF-I was capable of stimulating protein synthesis in cultured rat L6 myoblasts. Ligand blotting indicated changes in mammary gland secretion of IGFBP in response to WAP-DES expression. Histological analysis of mammary tissue from mice overexpressing des(1-3)hIGF-I showed incomplete mammary involution, ductile hypertrophy, and loss of secretory lobules associated with increased deposition of collagen. These changes are believed to occur through autocrine and paracrine effects of des(1-3)-hIGF-I on both epithelial and stromal cells.

Regulation of mammary gland factor/Stat5a during mammary gland development

The rat homolog of sheep mammary gland factor (MGF)/Stat5 has been isolated and used to study the regulation of Stat5 during mammary gland development and PRL regulation in COS cells transfected with Stat5a and the PRL receptor. Two alternatively spliced isoforms, designated Stat5a1 and Stat5a2, were identified, the latter encoding a carboxy-terminal truncated protein. A polyclonal antibody to a carboxy-terminal peptide of Stat5a1 was generated and used to measure the level of this isoform during mammary gland development and after PRL induction in COS cells transiently transfected with Stat5a and the long form of the PRL receptor. Surprisingly, Stat5a mRNA and protein were readily detected both in virgin rats and after mammary gland involution. The levels of Stat5a increased during pregnancy, were highest in late pregnancy, and then, unexpectedly, decreased during lactation, the time at which the highest levels of milk protein gene expression are observed. Electrophoretic mobility shift assays using the specific anti-Stat5a1 antisera demonstrated that Stat5a1 comprises part of the heterogeneous, PRL-inducible, protein-DNA complex associated with the beta-casein GAS site. Immunocytochemical analysis detected considerable cytoplasmic and some nuclear staining for Stat5a1 during late pregnancy and predominantly nuclear staining during early lactation. The lack of correspondence of Stat5a gene expression and beta-casein gene expression suggests that Stat5 activation may facilitate the interaction of other factors binding within composite response elements identified recently in the milk protein gene promoters that are then responsible for the stable expression of milk protein genes in terminally differentiated mammary epithelial cells.

Delay of dimethylbenz[a]anthracene-induced mammary tumorigenesis in transgenic mice by apoptosis induced by an unusual mutant p53 protein

Murine p53 containing an Arg-->Leu substitution at amino acid 172 possesses many properties characteristic of wild-type p53, including the ability to induce p21/WAF/Cip1 and apoptosis. To determine if p53-dependent apoptosis plays a critical role in mammary tumorigenesis, transgenic mice were generated in which the expression of this mutant p53 protein was targeted to the mammary gland by using the rat whey acidic protein gene promoter. Mice bearing pituitary isografts were treated with 7,12-dimethylbenz[a]anthracene (DMBA) and examined for mammary tumor development. Mice overexpressing the p53 transgene exhibited a statistically significant increase in apoptosis in the mammary gland and a statistically significant decrease in the incidence of DMBA-induced mammary tumors. No difference in tumor incidence was observed in mice without pituitary isografts who were treated with DMBA, because the transgene is not overexpressed in the absence of hormone stimulation provided by the pituitary isograft. The unexpected wild-type properties of the 172Arg-->Leu mutant p53, including its ability to stimulate apoptosis, make it a possible candidate for use in gene therapy protocols.

A finite-element facial model for simulating plastic surgery

CAPS (Computer-Aided Plastic Surgery) is a prototype computer program that uses a three-dimensional graphic model of a human face and incorporates a finite-element mathematical model of the physical properties of the soft tissue. This program can estimate the biomechanic consequences of ablation and rearrangement of tissue. The results of two hypothetical surgeries on the face are presented: A surgeon could use this program as a sketch pad to predict and compare the outcome of facial plastic procedures on a patient-specific model. The relation of this program to previous work is discussed, and directions for research and possible applications are addressed.

Developmentally and hormonally regulated CCAAT/enhancer-binding protein isoforms influence beta-casein gene expression

A highly conserved CCAAT/enhancer-binding protein (C/EBP)-binding site centered around -134 relative to the transcription start site in the rat beta-casein gene promoter is capable of interacting specifically with recombinant and mammary gland C/EBP proteins. Western blot analysis indicates that C/EBP levels change dramatically throughout mammary gland development. C/EBP alpha expression is barely detectable in mammary glands from virgin and pregnant animals but is expressed at high levels during lactation and at lower levels during involution. The expression of three C/EBP beta isoforms [the liver-enriched activating proteins (LAPs); and the liver-enriched inhibiting protein (LIP)] is elevated throughout pregnancy, with LIP expression increasing more than 100-fold. Thus, during pregnancy, a low LAP/LIP ratio (< 5) is maintained. C/EBP beta expression decreases at parturition, with LIP diminishing to levels observed in the virgin gland. Therefore, during lactation a more than 100-fold increase in the LAP/LIP ratio is observed. Treatment of the HC11 mammary epithelial cell line with hydrocortisone results in a 10- to 20-fold inhibition of LIP expression, with only minor changes in LAP levels. Therefore, glucocorticoids may impinge upon beta-casein gene expression by altering the ratio of the inhibitory to the activating isoforms of C/EBP beta. Several previously defined casein gene promoter regions capable of conferring hormone and extracellular matrix inducibility to reporter genes in mammary cells are suggested to be composite response elements, containing putative binding sites for the same set of hormonally and developmentally regulated factors: C/EBP, MGF/Stat5, and the glucocorticoid receptor.

Production of human surfactant protein C in milk of transgenic mice

Respiratory distress syndrome (RDS), caused by lack of pulmonary surfactant, affects 65 000 infants annually in the USA. Surfactant replacement therapy reduces the morbidity and mortality associated with RDS. Human surfactant protein C (SP-C) is an important component of pulmonary surfactant. To produce human SP-C, a construct using the rat whey acidic protein (WAP) promoter and 3' untranslated regions to target expression of the human SP-C gene to the mammary gland of transgenic mice was created. WAP/SP-C mRNA expression was detected in all transgenic lines analysed. SP-C was expressed in a copy-number-dependent and integration-site-independent fashion, with levels of expression ranging from 0.01% to 36.0% of the endogenous mouse WAP mRNA, and WAP/SP-C mRNA expression levels were greater than those of of the endogenous mouse lung SP-C mRNA. Expression at the RNA level was specific to the mammary gland and paralleled the endogenous WAP expression pattern during mammary gland development. Expression and secretion of the SP-C protein in the lactating mammary gland was demonstrated by western blots performed on whole milk using an anti-SP-C polyclonal antibody. Immunoreactive proteins of MW 22 and 12-14 kDa appeared only in transgenic milk. The 22 kDa protein represents the proprotein, and the 12-14 kDa is a processed form of SP-C.

Position-independent expression of whey acidic protein transgenes

The expression of a 3-kilobase genomic rat whey acidic protein (WAP) clone (-949/+2020) in transgenic mice has been demonstrated previously to be copy number-dependent and independent of the site of integration (Dale, T., Krnacik, M. J., Schmidhauser, C., Yang, C. Q.-L., Bissell, M. J., and Rosen, J. M. (1992) Mol. Cell. Biol. 12, 905-914). The present study demonstrated that position-independent expression of the rat WAP -949/+2020 transgene was dependent on transgene spacing. Position-independent expression also was inhibited by an internal replacement of 49 base pair within the conserved GC-rich 3'-untranslated region (3'-UTR) with an identically sized nonspecific DNA sequence. Using electrophoretic mobility shift assays, nuclear factors isolated from mouse and human cells were shown to associate specifically with the rWAP 3'-UTR DNA, but not with the 3'-UTR containing the internal replacement or specific point mutations. Since a single copy of the 3'-UTR inserted 5' of the promoter could not rescue the 3'-UTR deletion, the 3'-UTR element does not appear to be functioning as either a classic enhancer or insulator element. However, the level of expression of rWAP transgenes was correlated with transgene association with the chromosomal scaffold in vivo.

Effect of a face mask on respiratory water loss during sleep in cold conditions

The purpose of this study was to test the hypothesis that a heat-and-moisture-retaining mask would result in a significant decrease in respiratory water loss among healthy subjects sleeping in a cold environment. The study was done in a backyard near a tertiary-care center during winter nights with ambient temperatures of less than 0 degrees C. Subjects were 10 healthy volunteers, 8 males and 2 females, aged 23-40 years, with a mean of 30.9 years. In a crossover design study, subjects slept alone in mountaineering tents on two nights (8 h each night) using sleeping bags and ground insulation. On one night, they wore heat-and-moisture-retaining masks designed for cold weather exercise. On the other night, they wore no mask. Subjects were weighed before and after each session to obtain an estimate of respiratory water loss. Comparisons were made of weight loss with and without the mask. We found the use of the masks resulted in decreased weight loss in all but one subject. The mean reduction in weight loss was 0.13 kg (SD +/- 0.18 kg). Using a one-tailed t-test, this difference was found to be significant (p < .05). We conclude that the use of a simple and inexpensive face mask can result in a meaningful decrease in overnight respiratory water loss while sleeping in a cold environment.

Prostate cancer in a transgenic mouse

Progress toward understanding the biology of prostate cancer has been slow due to the few animal research models available to study the spectrum of this uniquely human disease. To develop an animal model for prostate cancer, several lines of transgenic mice were generated by using the prostate-specific rat probasin promoter to derive expression of the simian virus 40 large tumor antigen-coding region. Mice expressing high levels of the transgene display progressive forms of prostatic disease that histologically resemble human prostate cancer, ranging from mild intraepithelial hyperplasia to large multinodular malignant neoplasia. Prostate tumors have been detected specifically in the prostate as early as 10 weeks of age. Immunohistochemical analysis of tumor tissue has demonstrated that dorsolateral prostate-specific secretory proteins were confined to well-differentiated ductal epithelial cells adjacent to, or within, the poorly differentiated tumor mass. Prostate tumors in the mice also display elevated levels of nuclear p53 and a decreased heterogeneous pattern of androgen-receptor expression, as observed in advanced human prostate cancer. The establishment of breeding lines of transgenic mice that reproducibly develop prostate cancer provides an animal model system to study the molecular basis of transformation of normal prostatic cells and the factors influencing the progression to metastatic prostate cancer.

Nuclear factor I and mammary gland factor (STAT5) play a critical role in regulating rat whey acidic protein gene expression in transgenic mice

The rat whey acidic protein (WAP) gene contains a mammary gland-specific and hormonally regulated DNase I-hypersensitive site 830 to 720 bp 5' to the site of transcription initiation. We have reported previously that nuclear factor I (NFI) binding at a palindromic site and binding at a half-site are the major DNA-protein interactions detected within this tissue-specific nuclease-hypersensitive region. We now show that point mutations introduced into these NFI-binding sites dramatically affect WAP gene expression in transgenic mice. Transgene expression was totally abrogated when the palindromic NFI site or both binding sites were mutated, suggesting that NFI is a key regulator of WAP gene expression. In addition, a recognition site for mammary gland factor (STAT5), which mediates prolactin induction of milk protein gene expression, was also identified immediately proximal to the NFI-binding sites. Mutation of this site reduced transgene expression by approximately 90% per gene copy, but did not alter tissue specificity. These results suggest that regulation of WAP gene expression is determined by the cooperative interactions among several enhancers that constitute a composite response element.