Mammary Fetal Gland: Identification of New Oncofetal Antigens by Monoclonal Antibodies B72.3, MM1.80 and 4.36

Aims and Background

The B72.3, MM1.80 and 4.63 monoclonal antibodies directed against tumor-associated antigens react in human breast also with metaplastic, preneoplastic and metastatic cells, whereas they do not react with normal adult mammary tissue. The aim of our study was to point out the expression of these antigens during mammary gland development, since tumor-associated antigens are known to represent antigens of differentiation.

Study design

Fifty female fetal breasts between 20 and 40 weeks of gestational age were studied.

Results

Mammary tissue was identified only in 15 cases. B72.3, MM1.80 and 4.36 monoclonal antibodies reacted with epithelial antigens and maintained the same location and intensity in the various gestational ages. Immunoreactivity was weak, cytoplasmic and widespread for the 4.36 monoclonal antibody, intense and cytoplasmatic in a large number of cells for the B72.3 monoclonal antibody, and intense and luminal for the MM1.80 monoclonal antibody.

Conclusions

Such data further support the hypothesis that the normal process of development and differentiation can occur during tumor progression processes. Identification of these new oncofetal markers could offer a new perspective able to recognize the different phases of neoplastic progression and could be useful for prevention.

Transcriptional coregulator RIP140: an essential regulator of physiology

Transcriptional coregulators drive gene regulatory decisions in the transcriptional space. Although transcription factors including all nuclear receptors provide a docking platform for coregulators to bind, these proteins bring enzymatic capabilities to the gene regulatory sites. RIP140 is a transcriptional coregulator essential for several physiological processes, and aberrations in its function may lead to diseased states. Unlike several other coregulators that are known either for their coactivating or corepressing roles, in gene regulation, RIP140 is capable of acting both as a coactivator and a corepressor. The role of RIP140 in female reproductive axis and recent findings of its role in carcinogenesis and adipose biology have been summarised.

The mammary stem cell hierarchy: a looking glass into heterogeneous breast cancer landscapes

The mammary gland is a dynamic organ that undergoes extensive morphogenesis during the different stages of embryonic development, puberty, estrus, pregnancy, lactation and involution. Systemic and local cues underlie this constant tissue remodeling and act by eliciting an intricate pattern of responses in the mammary epithelial and stromal cells. Decades of studies utilizing methods such as transplantation and lineage-tracing have identified a complex hierarchy of mammary stem cells, progenitors and differentiated epithelial cells that fuel mammary epithelial development. Importantly, these studies have extended our understanding of the molecular crosstalk between cell types and the signaling pathways maintaining normal homeostasis that often are deregulated during tumorigenesis. While several questions remain, this research has many implications for breast cancer. Fundamental among these are the identification of the cells of origin for the multiple subtypes of breast cancer and the understanding of tumor heterogeneity. A deeper understanding of these critical questions will unveil novel breast cancer drug targets and treatment paradigms. In this review, we provide a current overview of normal mammary development and tumorigenesis from a stem cell perspective.

Pluripotency Genes and Their Functions in the Normal and Aberrant Breast and Brain

Pluripotent stem cells (PSCs) attracted considerable interest with the successful isolation of embryonic stem cells (ESCs) from the inner cell mass of murine, primate and human embryos. Whilst it was initially thought that the only PSCs were ESCs, in more recent years cells with similar properties have been isolated from organs of the adult, including the breast and brain. Adult PSCs in these organs have been suggested to be remnants of embryonic development that facilitate normal tissue homeostasis during repair and regeneration. They share certain characteristics with ESCs, such as an inherent capacity to self-renew and differentiate into cells of the three germ layers, properties that are regulated by master pluripotency transcription factors (TFs) OCT4 (octamer-binding transcription factor 4), SOX2 (sex determining region Y-box 2), and homeobox protein NANOG. Aberrant expression of these TFs can be oncogenic resulting in heterogeneous tumours fueled by cancer stem cells (CSC), which are resistant to conventional treatments and are associated with tumour recurrence post-treatment. Further to enriching our understanding of the role of pluripotency TFs in normal tissue function, research now aims to develop optimized isolation and propagation methods for normal adult PSCs and CSCs for the purposes of regenerative medicine, developmental biology, and disease modeling aimed at targeted personalised cancer therapies.

Breast diseases in adolescents

Fibroadenomas and breast growth disorders are the most common breast diseases in adolescent women. Assessment of breast disorders in this age group generally involves clinical evaluation through history and physical examination and when is needed ultrasonography. Due to the absence of breast cancer in adolescent women, it is easy to reassure women at the first consultation. Breast growth disorders can lead great psychological and physical embarrassment. Treatment consists of surgical procedures when the cosmetic defect is severe. According to the ANDI classification, small fibroadenomas are normal, clinical fibroadenomas are a mild aberration of the normal processes, and giant or multiple fibroadenomas are placed to the disease end of the spectrum. Fibroadenomas can be treated conservatively provided diagnosis is confident. Giant fibroadenomas are treated by surgical enucleation. Breast abscess is mainly due to the duct ectasia. In adolescence, ectasia has been described as an exaggeration of sinus duct development and can be considered as a variant of normality. Diseases of the adolescent breast are usually benign and their management are simple using medical strategy and more rarely surgical therapy.

Stem cells and breast cancer, where we are? A concise review of literature

There is an analogy between embryogenesis and cancer and the attention is on increasing the rate of cell division and on a small percentage of perennial cells . The key to understanding is to be found in the properties of these cells developed in the form of perennial totipotency, multipotency and unipotent. The normal life cycle involves epigenetic mechanisms that are deregulated in cancer cells, these tumor cells appear to belong to deregulation since its progeny. Here is a review of the literature on embryogenesis of the breast, endocrine system interactions Delna the proper development and functioning of the various cell lines and to the importance of cancer stem cells.

[Endocrine disruptor compounds and their role in the developmental programming of the reproductive axis]

Different perturbations during fetal and postnatal development unleash endocrine adaptations that permanently alter metabolism, increasing the susceptibility to develop later disease, process known as "developmental programming." Endocrine disruptor compounds (EDC) are widely spread in the environment and display estrogenic, anti-estrogenic or anti-androgenic activity; they are lipophilic and stored for long periods in the adipose tissue. Maternal exposure to EDC during pregnancy and lactation produces the exposure of the fetus and neonate through placenta and breast milk. Epidemiological and experimental studies have demonstrated reproductive alterations as a consequence of intrauterine and/or neonatal exposure to EDC. Diethystilbestrol (DES) is the best documented compound, this synthetic estrogen was administered to pregnant women in the 1950s and 1960s to prevent miscarriage. It was implicated in urogenital abnormalities in children exposed in utero and was withdrawn from the market. The "DES daughters" are women with high incidence of vaginal hypoplasia, spontaneous abortion, premature delivery, uterine malformation, menstrual abnormalities and low fertility. The "DES sons" show testicular dysgenesis syndrome, which is characterized by hypospadias, cryptorchidism and low semen quality. This entity is also associated wtih fetal exposure to anti-androgens as flutamide. The effects on the reproductive axis depend on the stage of development and the window of exposure, as well as the dose and the compound. The wide distribution of EDC into the environment affects both human health and ecosystems in general, the study of their mechanisms of action is extremely important currently.

Signalling pathways implicated in early mammary gland morphogenesis and breast cancer

Specification of mammary epithelial cell fate occurs during embryogenesis as cells aggregate to form the mammary anlage. Within the embryonic mammary bud, a population of epithelial cells exists that will subsequently proliferate to form a ductal tree filling the stromal compartment, and which can produce milk upon terminal differentiation after birth. Subsequently, these structures can be remodelled and returned to a basal state after weaning before regenerating in future pregnancies. The plasticity of the mammary epithelial cell, and its responsiveness to hormone receptors, facilitates this amazing biological feat, but aberrant signalling may also result in unintended consequences in the form of frequent malignancies. Reflecting this intimate connection, a considerable number of signalling pathways have been implicated in both mammary gland morphogenesis and carcinogenesis.

Hormonal and local control of mammary branching morphogenesis

Unlike other branched organs, the mammary gland undergoes most of its branching during adolescent rather than embryonic development. Its morphogenesis begins in utero, pauses between birth and puberty, and resumes in response to ovarian estrogens to form an open ductal tree that eventually fills the entire mammary fat pad of the young female adult. Importantly, this "open" architecture leaves room during pregnancy for the organ to develop milk-producing alveoli like leaves on otherwise bare branches. Thereafter, the ducts serve to deliver the milk that is produced throughout lactation. The hormonal cues that elicit these various phases of mammary development utilize local signaling cascades and reciprocal stromal-epithelial interactions to orchestrate the tissue reorganization, differentiation and specific activities that define each phase. Fortunately, the mammary gland is rather amenable to experimental inquiry and, as a result, we have a fair, although incomplete, understanding of the mechanisms that control its development. This review discusses our current sense and understanding of those mechanisms as they pertain to mammary branching, with the caveat that many more aspects are still waiting to be solved.

ErbB receptors and their ligands in the breast

ErbB receptor tyrosine kinases are membrane-bound receptors that possess intrinsic, ligand-activated, tyrosine kinase activity. Binding of growth factors to these receptors induces the formation of ErbB homo- and heterodimers and initiates a signalling cascade that traverses the cytoplasm to communicate with the nucleus and the cytoskeleton. The effect of this cascade is the regulation of cellular proliferation, differentiation, apoptosis, migration and adhesion. Although ErbB signalling is important for normal growth and development in the breast, a dysregulation of ErbB activity can lead to tumourigenesis. This review will focus on the role of ErbB signalling in both normal mammary gland development and breast cancer, with an emphasis on the mechanisms behind receptor activation and the therapeutic agents designed to inhibit ErbB activity.

Endocrine-disrupting compounds and mammary gland development: early exposure and later life consequences

Breast cancer is the most common non-skin cancer among women in this country. Breast cancer risk is significantly influenced by genetics, but over 70% of the women that are diagnosed have noninherited or sporadic cancer. The risk of breast cancer is thought to be modified by lifestyle and environment. Exposures to certain chemicals and hormone-mimicking or endocrine-disrupting compounds (EDCs) are suspected of contributing to increased breast cancer incidence as well as precocious puberty in the United States. Studies of EDC effects in rodents indicate that multiple toxicants can alter mammary gland development, with or without changing other markers of puberty. EDCs can cause transient and persistent effects on mammary gland development depending on dose, exposure parameters, and whether exposure was during critical periods of gland growth or differentiation. Adverse effects from these abnormal developmental patterns include the presence of carcinogen-sensitive structures in greater numbers or for longer periods in the gland and inhibited functional differentiation leading to malnutrition or increased mortality of their offspring. Developmental toxicants of the mammary gland could lead to an increase in the incidence of mammary tumors if they alter circulating or tissue-localized hormone levels, gland receptor expression patterns, hormone transport, or metabolism that results in altered response to endogenous hormones or growth factors. Environmental disruptors of rodent mammary gland development must be identified for informed decisions in epidemiological studies aimed at identification of environmental factors contributing to breast cancer risk, altered breast development during puberty, or inability to produce sufficient breast milk.

Characterization of the stimulatory effect of medroxyprogesterone acetate and chlormadinone acetate on growth factor treated normal human breast epithelial cells

OBJECTIVE

Evidence is increasing that adding progestogens to hormone replacement therapy may be more harmful than beneficial, however it is debatable whether all progestogens act equally on breast cells. Mitogenic growth factors from stromal breast tissue are important in growth-regulation of breast cells, and may modify responses to progestogens. We investigated the effect of two C-21 derivatives, medroxyprogesterone acetate (MPA) and chlormadinone acetate (CMA) on growth-factor treated normal breast epithelial cells and tried to explore the underlying mechanisms of proliferation.

METHOD

MCF10A (human epithelial, estrogen- and progesterone-receptor negative normal breast cells) were incubated with MPA or CMA at 0.1 and 1 microM for 7 days with the growth factors (GFs) EGF, bFGF and IGF-I at 1pM. The same combinations, as well as growth factors alone, were also incubated with the proliferation inhibitors PD98059 and LY294002 at 1 microM for 4 days. Cell proliferation rate was measured by the ATP-assay.

RESULTS

MPA 0.1 and 1 microM, and CMA 1 microM in combination with GFs both significantly increased cell proliferation rate, with MPA having the greatest effect. MPA- and CMA-induced proliferation of GF stimulated cells was blocked by both PD98059 (selective inhibitor of MAP kinases) and LY294002 (phosphatidylinositol 3-kinase inhibitor); GF stimulated cells could not be significantly reduced by any of the inhibitors used.

CONCLUSION

MPA and CMA have a stimulatory effect on benign growth factor stimulated MCF10A cells, possibly via activation of MAP kinase and subsequent substrates and activation of PI3-kinase. GF induced proliferation appear to be mediated by pathways other than those investigated here. Growth factors and progestogens therefore have an additive, synergistic effect on cell proliferation, eliciting their effects via different pathways.

Key stages of mammary gland development: molecular mechanisms involved in the formation of the embryonic mammary gland

The development of the embryonic mammary gland involves communication between the epidermis and mesenchyme and is coordinated temporally and spatially by various signaling pathways. Although many more genes are likely to control mammary gland development, functional roles have been identified for Wnt, fibroblast growth factor, and parathyroid hormone-related protein signaling. This review describes what is known about the molecular mechanisms that regulate embryonic mammary gland development.

Mammary gland development and cancer

The mammary gland is a complex organ that begins development early in gestation and constantly changes in size, shape and function from the time of puberty to menopause. The earliest stages of embryogenesis appear to be independent of steroid hormones, whereas after the 15th week breast structure is largely influenced by a variety of hormones. In most females, further breast development begins at puberty under the influence of cyclical estrogen and progesterone secretion. This process may continue into the 20s and it is enhanced by pregnancy. Growth and transcription factors contribute to the reciprocal stromal-epithelial interactions in growth, development and tumorogenesis of the mammary gland. From the embryological point of view the morphology of both mammary ductal and lobular cells results from the same developmental process. Numerous data suggest the existence of self-renewing, pluripotent mammary stem cells but their molecular characteristics and differentiation pathways are unknown. The extensive research currently being done in molecular biology and pathology, cancer genomics and proteomics will hopefully contribute to further elucidation of all the genetic and environmental factors involved in the development, differentiation, and involution of the mammary gland and this may give insight into the etiopathogenesis, early detection, treatment, and potential prevention of breast cancer.

Intrauterine breast development and the mammary myoepithelial lineage

As their name implies, the myoepithelial cells found at the epithelial-mesenchymal interface of the human mammary gland disclose features suggestive of a dual epithelial-like and muscle-like differentiation, i.e. they co-express various keratins and vimentin intermediate filaments, as well as smooth muscle-related antigens. This article provides an overview of the literature on intrauterine breast development with special emphasis on the myoepithelial component of the fetal human mammary gland epithelium. It discusses original and recently published immunohistochemical data on myoepithelial precursors and reasserts the relevance of developmental, morphological fetal tissue-based studies to the understanding and the clinical management of adult diseases.

Nodal and Cripto-1: embryonic pattern formation genes involved in mammary gland development and tumorigenesis

Members of the TGFbeta superfamily and EGF-CFC family, such as Nodal and Cripto, are important mediators of anterior-posterior and left-right axis specification during embryogenesis. In this paper, we review the role of Nodal and Cripto as critical morphogen-like molecules, with an emphasis on Nodal and EGF-CFC signaling during embryonic pattern formation. New evidence from gene expression and transgenic mouse studies have shown that both Nodal and Cripto-1 are expressed within the mammary duct and that modulation of these genes can disrupt normal branching morphogenesis resulting in epithelial disorganization and defective ductal architecture. We describe these new findings and propose that Cripto and Nodal are candidate mammary morphogens. Finally, the data linking overexpression of Cripto and perturbations of Cripto signaling to cell transformation and tumor formation are discussed. The fact that Cripto can modulate multiple pathways suggests it may act to deregulate growth inhibitors/homeostasis factors early in the cell transformation process and then activate prosurvival pathways dependent on MAPK and PI3K/Akt later in fully transformed phenotypes.

Msx-1 and Msx-2 in mammary gland development

Homeobox genes do not generally function alone to determine cell fate and morphogenesis. Rather it is the distinct combination of various members of the homeobox family of genes and their spatiotemporal patterns of expression that determine cell identity and function. Functional redundancy often makes it difficult to clearly discern the role of any one given homeobox gene. The roles that Msx1 and Msx2 play in branching morphogenesis of the mammary gland are only now becoming more evident. Many signaling pathways and transcription factors are implicated in how these homeobox genes correctly determine the morphological development of the gland. Overexpression of Msx1 and Msx2 may also be involved in tumorigenesis. Additional studies are needed to elucidate the roles of these genes in both breast development and cancer.

A crucial role for fibroblast growth factor signaling in embryonic mammary gland development

The fibroblast growth factors (Fgfs) represent a large group of intercellular signaling molecules that mediate their effects by binding to a class of cell surface enzymes belonging to the receptor tyrosine kinase family (FgfRs). In vitro, Fgf signaling can induce potent mitogenic, motogenic, and angiogenic cellular responses, and has been associated with a multitude of biological processes. The development of gene targeting and transgenic strategies has provided unequivocal evidence for the key involvement of Fgf signaling in mammalian developmental processes. In this review we highlight recent findings that demonstrate a critical requirement for Fgf signaling in the induction and development of the embryonic mammary gland. Furthermore, we briefly discuss the potential of Fgfs to act as oncogenic factors in mammary neoplasia.

The role of Tbx2 and Tbx3 in mammary development and tumorigenesis

TBX2 and TBX3 are members of a family of genes encoding developmental transcription factors, characterized by a 200 amino acid DNA binding domain (T-box). Tbx2 and Tbx3 are closely related T-box proteins that have been implicated in development of a number of different tissues including the mammary gland. TBX3 is required for normal mammary development in mouse models and in patients with ulnar-mammary syndrome (UMS). In addition to a role in development, TBX2 and TBX3 have been implicated in tumor development through downregulation of the alternative reading frame (ARF) tumor suppressor and an associated bypass of senescence. Here we review the current information on the roles of Tbx2 and Tbx3 in mammary gland development and tumorigenesis.

Next stop, the twilight zone: hedgehog network regulation of mammary gland development

The hedgehog signal transduction network is a critical mediator of cell-cell communication during embryonic development. Evidence also suggests that properly regulated hedgehog network function is required in some adult organs for stem cell maintenance or renewal. Mutation, or misexpression, of network genes is implicated in the development of several different types of cancer, particularly that of skin, brain, lung, and pancreas. Recent studies in the mouse mammary gland have demonstrated roles for hedgehog network genes at virtually every phase of mammary gland development where it regulates such diverse processes as embryonic mammary gland induction, establishment of ductal histoarchitecture, and functional differentiation in lactation. Further, studies suggest a role for misregulated network function in the progression of breast cancer.

Notch signaling in mammary development and oncogenesis

With the discovery of an activated Notch oncogene as a causative agent in mouse mammary tumor virus induced breast cancer in mice, the potential role for Notch signaling in normal and pathological mammary development was revealed. Subsequently, Notch receptors have been found to regulate normal development in many organ systems. In addition, inappropriate Notch signaling has been implicated in cancer of several tissues in humans and animal model systems. Here we review important features of the Notch system, and how it may regulate development and cancer in the mammary gland. A large body of literature from studies in Drosophila and C. elegans has not only revealed molecular details of how the Notch proteins signal to control biology, but shown that Notch receptor activation helps to define how other signaling pathways are interpreted. In many ways the Notch system is used to define the context in which other pathways function to control proliferation, differentiation, cell survival, branching morphogenesis, asymmetric cell division, and angiogenesis--all processes which are critical for normal development and function of the mammary gland.

Roles of the transcription factors snail and slug during mammary morphogenesis and breast carcinoma progression

The zinc-finger transcription factors Snail and Slug are involved in different processes controlling cell differentiation and apoptosis. They also appear to be involved in tumor progression. Their putative involvement in mammary gland development has not been specifically examined so far. Slug is expressed at a significant level in normal breast, and indirect evidence suggests it could be implicated in tubulogenesis. As an antiapoptotic agent, it could also protect epithelial cells from death during ductal lumen formation and during breast involution. In breast carcinomas, Snail transcription factors have been linked to tumor progression and invasiveness. Possible mechanisms include repression of the E-cadherin gene by Snail or Slug. However, it is not clear how this transcriptional activity is implicated in vivo. Other possible mechanisms involve maintenance of a plastic phenotype by Slug that could participate in local invasion of ductal carcinomas, and interference with apoptotic pathways that could contribute to global tumor growth and radioresistance. These processes probably also involve interactions with estrogen, EGF, or c-kit pathways.

Wnt proteins in mammary development and cancer

Secreted proteins of the Wnt family play widespread roles in the regulation of embryonic development, and aberrant activation of the canonical Wnt/beta-catenin pathway is one of the most frequent signaling abnormalities known in human cancer. While the consequences of Wnt signaling in development are diverse at the cellular level, they are often concerned with cell fate determination. Recent data also indicate that Wnt proteins influence the self-renewal of stem cells in certain tissues. In the mammary gland, Wnt signals are strongly implicated in initial development of the mammary rudiments, and in the ductal branching and alveolar morphogenesis that occurs during pregnancy. Transgenic expression of Wnt1 or Wnt10b in the mouse mammary gland leads to lobuloalveolar hyperplasia with a major risk of progression to carcinoma. Recent evidence suggests that this phenotype is associated with expansion of a multipotent progenitor cell population. In human breast cancer, evidence of beta-catenin accumulation implies that the canonical Wnt signaling pathway is active in over 50% of carcinomas. However, specific mutations that might account for this activation of signaling have not yet been identified.

Progesterone involvement in breast development and tumorigenesis--as revealed by progesterone receptor "knockout" and "knockin" mouse models

In light of recent clinical trials, the debate concerning the risks and benefits of progestin-based postmenopausal hormone replacement therapy (HRT) has reached a renewed level of urgency. Irrespective of the position taken, the consensus is that more basic research needs to be performed to address progesterone's fundamental role in mammary development and tumorigenesis. Towards this end, the progesterone receptor knockout (PRKO) mouse demonstrated that progesterone is essential for pregnancy-associated mammary gland ductal side-branching and alveologenesis and that these morphological changes are dependent on progesterone-induced mammary epithelial proliferation. Importantly, the PRKO mouse showed that the progesterone-proliferative signal significantly contributes to mammary tumor susceptibility in an established mammary tumor model. Insight into the cellular mechanism(s) by which progesterone affects mammary morphogenesis has been disclosed by a new PR-LacZ knockin mouse, which revealed that PR's spatial expression pattern undergoes precise choreographed distributional changes that precede key stages in postnatal mammary development. In the case of early pregnancy, the segregation of cells undergoing progesterone-induced proliferation from those that express PR implicates a paracrine mode of action for progesterone-induced mammary epithelial proliferation, whereas the preparturient decline of PR expression underscores the need to remove this signal for full functional differentiation of this tissue. Our findings support the proposal that the mammary gland's normal response to the progesterone-signal is dependent upon specific spatial organizational patterns of PR expression and that derailment in these cellular processes may contribute to abnormal mammary development, including cancer. This review concludes by emphasizing the need to identify the downstream molecular targets that mediate progesterone's effects in this tissue. Identification of such targets will not only enhance our mechanistic understanding of progesterone's role in mammary development and cancer, but may also facilitate the formulation of new design strategies in breast cancer diagnosis and/or treatment.

Basal cells of second trimester fetal breasts: immunohistochemical study of myoepithelial precursors

The molecular characterization of human mammary myoepithelial cells is incomplete, hindering our understanding of its importance in breast physiology and pathology. Because data on the precursors of this cell lineage remain scarce and often contradictory, basal epithelial cells of second trimester fetal breasts were studied by light microscopy (LM) and immunohistochemistry (IHC). Up to 20 wk of gestational age, the mammary rudiments only comprised roundish primary outgrowths, "primary buds," more likely to represent immature nipples than true mammary tissue. At 21 wk secondary outgrowths, "projections," extended from enlarged primary buds into well-vascularized layers of dense mesenchyme. Basal projection cells had a partial myoepithelial-like phenotype: they reacted with CD29, CD49f, CD104, keratin 14, vimentin, S100beta protein, and p63; furthermore, many became positive for keratin 17, alpha-smooth muscle actin, and CD10 (but not for keratin 19) between wk 21 and 25. The continuous basement membrane associated with the fetal mammary rudiments was strongly positive for collagens type IV and VII, and for laminin 5. Consistently strong and basally polarized staining for hemidesmosomal components suggested that although incompletely differentiated, most second trimester myoepithelial precursors might already mediate local epithelial-mesenchymal interactions, i.e., complex signaling pathways which are crucial for both orderly growth during development and maintenance of homeostasis during adult life. Because they are likely implicated in the phenomenon of menstrual cycle-related growth spurts in the adult resting breast, the strategically positioned cells of the myoepithelial lineage might constitute critical protagonists in defective epithelial-mesenchymal signaling associated with cancer progression.

PEA3 transcription factors are expressed in tissues undergoing branching morphogenesis and promote formation of duct-like structures by mammary epithelial cells in vitro

The genetic program that controls reciprocal tissue interactions during epithelial organogenesis is still poorly understood. Erm, Er81 and Pea3 are three highly related transcription factors belonging to the Ets family, within which they form the PEA3 group. Little information is yet available regarding the function of these transcription factors. We have previously used in situ hybridization to compare their expression pattern during critical stages of murine embryogenesis [Oncogene 15 (1997), 937; Mech. Dev. 108 (2001), 191]. In this study, we have examined the expression of PEA3 group members during organogenesis of the lung, salivary gland, kidney, and mammary gland. In all of these developmental settings, we observed a tight correlation between branching morphogenesis and the expression of specific members of the PEA3 group. To assess the functional relevance of these findings, Erm and Pea3 were overexpressed in the TAC-2.1 mammary epithelial cell line, which has the ability to form branching duct-like structures when grown in collagen gels. We found that overexpression of Erm and Pea3 markedly enhances branching tubulogenesis of TAC-2.1 cells and also promotes their invasion into a collagen matrix. Collectively, these findings suggest that the differential expression of PEA3 group transcription factors has an important role in the regulation of branching morphogenesis and raise the question of their implication in branching signaling.

Transcriptional regulators in mammary gland development and cancer

The mammary gland represents a remarkable developmental system for the study of genetic programs underlying proliferation, differentiation and inductive tissue interactions. Mammary gland ontogeny occurs predominantly in the adult and involves a complex cycle of morphogenesis, with the continuous production, differentiation and apoptosis of mammary epithelial cells occurring with each pregnancy. Perturbations in pathways controlling any of these processes may lead to neoplasia. Substantial progress has been made in defining signaling pathways important for mammopoiesis, in particular those that mediate the effects of peptide and steroid hormones. However, much less is known about the transcriptional regulators that dictate cell specificity, proliferation and differentiation within the mammary gland. This review will discuss recent insights into the transcriptional networks important for mammary gland development and consider how deregulation of specific transcription factors contributes to the pathogenesis of breast cancer.

Tube or not tube: remodeling epithelial tissues by branching morphogenesis

Branching morphogenesis involves the restructuring of epithelial tissues into complex and organized ramified tubular networks. Early rounds of branching are controlled genetically in a hardwired fashion in many organs, whereas later, branching is stochastic, responding to environmental cues. We discuss this sequential process from formation of an organ anlage and invagination of the epithelium to branch initiation and outgrowth in several model systems including Drosophila trachea and mammalian lung, mammary gland, and kidney.

Do different branching epithelia use a conserved developmental mechanism?

Formation of branching epithelial trees from unbranched precursors is a common process in animal organogenesis. In humans, for example, this process gives rise to the airways of the lungs, the urine-collecting ducts of the kidneys and the excretory epithelia of the mammary, prostate and salivary glands. Branching in these different organs, and in different animal classes and phyla, is morphologically similar enough to suggest that they might use a conserved developmental programme, while being dissimilar enough not to make it obviously certain that they do. In this article, I review recent discoveries about the molecular regulation of branching morphogenesis in the best-studied systems, and present evidence for and against the idea of there being a highly conserved mechanism. Overall, I come to the tentative conclusion that key mechanisms are highly conserved, at least within vertebrates, but acknowledge that more work needs to be done before the case is proved beyond reasonable doubt.

Stromal effects on mammary gland development and breast cancer

Breast cancer manifests itself in the mammary epithelium, yet there is a growing recognition that mammary stromal cells also play an important role in tumorigenesis. During its developmental cycle, the mammary gland displays many of the properties associated with breast cancer, and many of the stromal factors necessary for mammary development also promote or protect against breast cancer. Here we review our present knowledge of the specific factors and cell types that contribute to epithelial-stromal crosstalk during mammary development. To find cures for diseases like breast cancer that rely on epithelial-stromal crosstalk, we must understand how these different cell types communicate with each other.

Establishing a framework for the functional mammary gland: from endocrinology to morphology

From its embryonic origins, the mammary gland in females undergoes a course of ductal development that supports the establishment of alveolar structures during pregnancy prior to the onset of lactogenesis. This development includes multiple stages of proliferation and morphogenesis that are largely directed by concurrent alterations in key hormones and growth factors across various reproductive states. Ductal elongation is directed by estrogen, growth hormone, insulin-like growth factor-I, and epidermal growth factor, whereas ductal branching and alveolar budding is influenced by additional factors such as progesterone, prolactin, and thyroid hormone. The response by the ductal epithelium to various hormones and growth factors is influenced by epithelial-stromal interactions that differ between species, possibly directing species-specific morphogenesis. Evolving technologies continue to provide the opportunity to further delineate the regulation of ductal development. Defining the hormonal control of ductal development should facilitate a better understanding of the mechanisms underlying mammary gland tumorigenesis.

Isolation of a murine homologue of the Drosophila neuralized gene, a gene required for axonemal integrity in spermatozoa and terminal maturation of the mammary gland

The Drosophila neuralized gene shows genetic interactions with Notch, Enhancer of split, and other neurogenic genes and is thought to be involved in cell fate specification in the central nervous system and the mesoderm. In addition, a human homologue of the Drosophila neuralized gene has been described as a potential tumor suppressor gene in malignant astrocytomas. We have isolated a murine homologue of the Drosophila and human Neuralized genes and, in an effort to understand its physiological function, derived mice with a targeted deletion of this gene. Surprisingly, mice homozygous for the introduced mutation do not show aberrant cell fate specifications in the central nervous system or in the developing mesoderm. This is in contrast to mice with targeted deletions in other vertebrate homologues of neurogenic genes such as Notch, Delta, and Cbf-1. Male Neuralized null mice, however, are sterile due to a defect in axoneme organization in the spermatozoa that leads to highly compromised tail movement and sperm immotility. In addition, female Neuralized null animals are defective in the final stages of mammary gland maturation during pregnancy.

Activins as regulators of branching morphogenesis

Development of glandular organs such as the kidney, lung, and prostate involves the process of branching morphogenesis. The developing organ begins as an epithelial bud that invades the surrounding mesenchyme, projecting dividing epithelial cords or tubes away from the site of initiation. This is a tightly regulated process that requires complex epithelial-mesenchymal interactions, resulting in a three-dimensional treelike structure. We propose that activins are key growth and differentiation factors during this process. The purpose of this review is to examine the direct, indirect, and correlative lines of evidence to support this hypothesis. The expression of activins is reviewed together with the effect of activins and follistatins in the development of branched organs. We demonstrate that activin has both negative and positive effects on cell growth during branching morphogenesis, highlighting the complex nature of activin in the regulation of proliferation and differentiation. We propose potential mechanisms for the way in which activins modify branching and address the issue of whether activin is a regulator of branching morphogenesis.

Windows in early mammary development: critical or not?

Two critical windows in mammary development have been proposed. The first arises from observations in rodents that nutrition during fetal and neonatal periods can affect mammary ductular outgrowth, subsequent proliferative activity and, eventually, tumorigenesis, that is, potentially it could have a long-term effect on pathological outcome (breast cancer) in women. The second similarly involves early diet, but in this case the outcome is phenotypic, in that dairy heifers reared too quickly during the peripubertal period subsequently show impaired udder development and reduced milk yield persisting throughout life. Most mammary development occurs during pregnancy, but this period is usually thought of only in terms of the immediate outcome for the subsequent lactation; it is not believed to be a critical window, at least in terms of lifetime mammary productivity. This review examines the evidence underlying these various claims and attempts to define the mechanisms involved, and also considers whether derangements occurring earlier in life (prenatally) could also have long-term consequences for physiological or pathological mammary development.

Fibroblast growth factor signalling in mouse mammary gland development

Fibroblast growth factors (Fgfs) and their receptors are important intercellular signalling molecules involved in many aspects of animal development. The aberrant expression of the Fgfs or the inappropriate activation of their cell surface receptors have been implicated in tumorigenesis. Here, we describe the evidence that as well as playing a critical role in the formation of the mammary primordia during embryogenesis, signalling by Fgfs is necessary for optimal lobuloalveolar development of the mouse mammary gland during pregnancy.

[A fundamental symmetry between morphogenesis and function of branched organs]

It is generally difficult to find any relationship between the morphogenesis of an organ and its final function. A priori, such a relationship has no reason to exist, since organs do not actually function during their formation. I will show in this article that, for a very large class of organs--the branched organs--there exists a hidden relationship between their morphogenesis and their function. This class of organs comprises: the lungs, the salivary mammary and lacrymal glands, the kidneys, the pancreas, and possibly other organs, such as testes. For all these organs, a fundamental fact that comes from recent developments in physics explains at the same time how they form, and why they work. This suggests, first, that complex organs are not the result of gradual and long selection processes, and, second, that this specific structure for the organs is imposed by the laws of physics. The growth process, as described here, is possibly the only one that allows both to build a fluid-secreting organ, and make it work.

Absence of functional type 1 parathyroid hormone (PTH)/PTH-related protein receptors in humans is associated with abnormal breast development and tooth impaction

Recent studies in transgenic mice have demonstrated that PTH-related protein (PTHrP), signaling through the type 1 PTH/PTHrP receptor (PTHR1), regulates endochondral bone development and epithelial-mesenchymal interactions during the formation of the mammary glands and teeth. Recently, it has been shown that loss-of-function mutations in the PTHR1 gene result in a rare, lethal form of dwarfism known as Blomstrand chondrodysplasia. These patients suffer from severe defects in endochondral bone formation, but abnormalities in breast and tooth development have not been reported. To ascertain whether PTHrP signaling was important to human breast and tooth development, we studied two fetuses with Blomstrand chondrodysplasia. These fetuses lack nipples and breasts. Developing teeth were present, but they were severely impacted within the surrounding alveolar bone, leading to distortions in their architecture and orientation. Compatible with the involvement of PTHR1 and PTHrP in human breast and tooth morphogenesis, both were expressed within the developing breasts and teeth of normal human fetuses. Therefore, impairment of the PTHrP/PTHR1 signaling pathway in humans is associated with severe abnormalities in tooth and breast development. In addition to regulating human bone formation, this signaling pathway is also necessary for the normal development of the human breast and tooth.

Mammary gland development and the prolactin receptor

Prolactin (PRL), synthesized by the anterior pituitary and to a lesser extent by numerous extrapituitary tissues, affects more physiological processes than all other pituitary hormones combined. This hormone is involved in > 300 separate effects in various vertebrate species where its role has been well documented. The initial step in its action is the binding to a specific membrane receptor which belongs to the superfamily of class 1 cytokine receptors. The function of this receptor is mediated, at least in part, by two families of signaling molecules: Janus kinases and signal transducers and activators of transcription. PRL-binding sites have been identified in a number of cells and tissues of adult animals. Disruption of the gene for the PRL receptor has provided a new animal model with which to better understand the actions of PRL on mammary morphogenesis and mammary gland gene expression. The recent availability of genetic mouse models provides new insights into mammary developmental biology and how the action of a hormone at specific stages of development can have effects later in life on processes such as mammary development and breast cancer initiation and progression.

Repression of the putative tumor suppressor gene Bard1 or expression of Notch4(int-3) oncogene subvert the morphogenetic properties of mammary epithelial cells

We have investigated whether repression of the putative tumor suppressor gene BARD1 or expression of the Notch4(int-3) oncogene in non-tumorigenic mammary epithelial cells affects their in vitro morphogenetic properties. Bard1 (Brca1-associated ring domain) is a protein interacting with Brca1 and thought to be involved in Brca1-mediated tumor suppression. To investigate the potential role of Bard1 in mammary gland development, we repressed its expression in TAC-2 cells, a murine mammary epithelial cell line which, when grown in three-dimensional collagen gels, forms branching ducts in response to hepatocyte growth factor (HGF) and alveolar-like cysts in response to hydrocortisone. Whereas Bard1 repression did not markedly modify the tubulogenic response of TAC-2 cells to HGF, it dramatically altered cyst development, resulting in the formation of compact cell aggregates devoid of central lumen. In addition, when grown to post-confluence in two-dimensional cultures, Bard1-suppressed TAC-2 cells overcame contact-inhibition of cell proliferation and formed multiple cell layers. The Notch4(int-3) oncogene, which codes for a constitutively activated form of the Notch4 receptor, has been reported to induce undifferentiated carcinomas when expressed in the mammary gland. The potential effect of activated Notch4 on mammary gland morphogenesis was investigated by retroviral expression of the oncogene in TAC-2 cells. Notch4(int-3) expression was found to significantly reduce HGF-induced tubulogenesis and to markedly inhibit hydrocortisone-induced cyst formation. In addition, Notch4(int-3) expressing TAC-2 cells formed multilayers in post-confluent cultures and exhibited an invasive behavior when grown on the surface of collagen gels. Taken together, these results indicate that both repression of Bard1 and expression of Notch4(int-3) disrupt cyst morphogenesis and induce an invasive phenotype in TAC-2 mammary epithelial cells.

[Complete supernumerary breast on the thigh in a male patient]

BACKGROUND

Supernumerary nipples are not rare but the developement of a complete supernumerary breast is exceptional.

CASE REPORT

A 59-year-old man presented a progressively increasing ancient right- groin-masse. The histopathologic examination of the lesion confirmed the diagnostic of polymastia.

DISCUSSION

The interest of this observation results from the very unusual occurence of polymastia (less than 1 p. 100 of supernumerary nipples), especially for a caucasian man. The prevalence appears to be higher in women and oriental people. Diagnostic of supernumerary nipple is difficult because of its atypical appearance and ectopic location. However, this diagnostic is important because ectopic breast tissue is subject to the same pathologic changes that occur in normally positioned breasts and it can be a marker for associated diseases such as urologic malformations or urogenital malignancies.

Cancer risk related to mammary gland structure and development

The breast undergoes dramatic changes in size, shape, and function in association with growth, reproduction, and post-menopausal regression. Those changes impact women's lifetime breast cancer risk. An early first full-term pregnancy exerts a protective effect, emphasizing the need for understanding the role of reproductive influences on breast development and on cancer initiation and progression, and providing a paradigm for developing preventive strategies based on physiological principles. Even though the cause of breast cancer and the ultimate mechanisms through which an early pregnancy protects from cancer development remain largely unknown, a likely explanation for this protection has been provided by experimental in vivo and in vitro models. These studies have led to the conclusions that cancer initiation requires the interaction of a carcinogen with an undifferentiated and highly proliferating mammary epithelium, whereas differentiation of the mammary gland inhibits carcinogenic initiation. The process of mammary gland differentiation is the result of complex interactions of ovarian, pituitary, and placental hormones, which in turn induce inhibition of cell proliferation, downregulation of estrogen and progesterone receptors, activation of specific genes, such as inhibin, mammary derived growth factor inhibitor and a serpin-like gene, and expression of extracellular matrix proteins in the normal breast. Cell immortalization and transformation are associated with the expression of ferritin H and S100P protein, which serve as markers of cancer initiation. Comparative studies of normal and neoplastic breast development have unraveled similarities with experimental models that validate the extrapolation of findings for testing hypotheses on the initiation and progression of breast cancer.

Transcriptional repression of oestrogen receptor by metastasis-associated protein 1 corepressor

Activation of the heregulin/HER2 pathway in oestrogen receptor (ER)-positive breast-cancer cells leads to suppression of oestrogen-receptor element (ERE)-driven transcription and disruption of oestradiol responsiveness, and thus contributes to progression of tumours to more invasive phenotypes. Here we report the identification of metastatic-associated protein 1 (MTA1), a component of histone deacetylase (HDAC) and nucleosome-remodelling complexes, as a gene product induced by heregulin-beta1 (HRG). Stimulation of cells with HRG is accompanied by suppression of histone acetylation and enhancement of deacetylase activity. MTA1 is also a potent corepressor of ERE transcription, as it blocks the ability of oestradiol to stimulate ER-mediated transcription. The histone-deacetylase inhibitor trichostatin A blocks MTA1-mediated repression of ERE transcription. Furthermore, MTA1 directly interacts with histone deacetylase-1 and -2 and with the activation domain of ER-alpha. Overexpression of MTA1 in breast-cancer cells is accompanied by enhancement of the ability of cells to invade and to grow in an anchorage-independent manner. HRG also promotes interaction of MTA1 with endogenous ER and association of MTA1 or HDAC with ERE-responsive target-gene promoters in vivo. These results identify ER-mediated transcription as a nuclear target of MTA1 and indicate that HDAC complexes associated with the MTA1 corepressor may mediate ER transcriptional repression by HRG.

Expression and function of Ets transcription factors in mammalian development: a regulatory network

The Ets transcription factor family is involved in a variety of mammalian developmental processes at the cellular, tissue and organ levels. They are implicated in cellular proliferation, differentiation, migration, apoptosis and cell - cell interactions. This article reviews recent studies that demonstrate the integral importance of Ets in the dosage dependent regulation of development. The expression of many Ets genes is associated with mesenchymal - epithelial interactions and changes in extracellular matrix proteins. These inductive processes contribute to tissue remodeling and integrity, particularly during embryonic development. Overlapping as well as unique patterns of Ets expression are evident in developing tissues, including development of the lymphoid and myeloid lineages, brain and central nervous system, bone and mammary gland. Integration of these data will allow the development of predictive models for the regulation of complex developmental processes.

Oestrogen receptor alpha in female fetal, infant, and child mammary tissue

Oestrogen receptor alpha (ER alpha) expression was studied in female mammary tissue from a series of 35 samples obtained post-mortem, ranging from fetuses of 13 weeks' gestation to prepubertal children of 12 years. Immunocytochemistry was performed on formalin-fixed tissue after microwave antigen retrieval. ER alpha was present in epithelial cell nuclei from the 30th week of gestation onwards and was markedly up-regulated shortly after birth. For up to 3 months thereafter, progesterone receptor was also expressed, indicative that the ER alpha was functional. During this period, ER alpha was also present in epithelial cell cytoplasm. From this perspective of the developing breast, it is suggested that an early postnatal component should be added to the prenatal oestrogen hypothesis; further, the significance of ER alpha cytoplasmic staining in the adult breast also merits review.

Bio-morphological events in the development of the human female mammary gland from fetal age to puberty

Bio-morphological understanding of the developing human mammary glands may clarify some aspects of breast pathology, including cancer. In particular, some epidemiological data suggests that during fetal growth an altered intrauterine hormonal status, especially a change in estrogen status, could predispose to carcinogenesis. In an attempt to achieve new information on early breast growth, a series of developing human breasts have been analyzed, namely: 4 fetal breasts (28-32 weeks of gestational age), 7 infant breasts (7 h to 2 years) and 1 puberal breast (12 years). In addition to the morphological features, we studied the immunohistochemical expression of some markers involved in morphogenesis, such as MIB-1 for cell proliferation, bcl-2 for apoptosis control, CD34 for vasculogenesis, estrogen (ER) and progesterone (PR) receptors for hormonal profile, and smooth-muscle actin for myoepithelial differentiation. The results were as follows: (a) lobules, absent between 28 weeks and 2 days, were well evident at 2 years of age and at puberty; (b) myoepithelial cells appeared from 28 weeks onward and persisted later with no modification in quantity and distribution; (c) epithelial cell proliferation was constantly low; (d) in all breasts inner epithelial cells showed diffuse bcl-2 positivity, while basal myoepithelial-like cells were generally negative; (e) all breasts were well vascularized with two different patterns: periductal vascularization (PDV) and interductal vascularization (IDV), IDV being always present, whereas PDV was found only in infant breasts; (f) ER and PR were almost absent in fetal and infant breasts, while their expression was high in the epithelial cells of the puberal breast; (g) stromal cells had no hormonal receptors and were heterogeneous for proliferation and bcl-2 expression. Interestingly, two fetal breasts showed high proliferation and high ER expression, respectively, in their epithelial compartment. This could be the expression of an altered hormonal environment in utero, representing a basis for possible subsequent cancer initiation.

Human breast development

This review presents an atlas of the histology of the normal physiological states of the human breast including prenatal, prepubertal, and pubertal development, adult resting gland, pregnancy, lactation, and postinvolution. The aim is to produce a pictorial overview of the main stages in development and the common findings in the adult that are considered to be within the range of normality. Unlike inbred strains of animals, in humans it is clear that the chronology of ductal and lobular development is not predictable, either in the fetus, the infant, the peripubertal breast, or the adult. This is probably due to the individual variation in hormone levels both in utero and after birth. For many of the developmental time points there are very little data available. In this review we indicate the current state of knowledge of human breast development and some of the main similarities and differences with the rodent, the main animal model. The major phases of growth and development are described and accompanied by photographs that are representative of each stage. Stress is placed on terminology as there is confusion in the literature. This article is written as an accessory to the companion review on breast cancer.