Directed differentiation of human embryonic stem (hES) cells and human induced pluripotent stem (hiPS) cells captures in vivo developmental pathways for specifying lineages in vitro, thus avoiding perturbation of the genome with exogenous genetic material. Thus far, derivation of endodermal lineages has focused predominantly on hepatocytes, pancreatic endocrine cells and intestinal cells1–5. The ability to differentiate pluripotent cells into anterior foregut endoderm (AFE) derivatives would expand their utility for cell therapy and basic research to tissues important for immune function, such as the thymus; for metabolism, such as thyroid and parathyroid; and for respiratory function, such as trachea and lung. We find that dual inhibition of transforming growth factor (TGF)-β and bone morphogenic protein (BMP) signaling after specification of definitive endoderm from pluripotent cells results in a highly enriched AFE population that is competent to be patterned along dorsoventral and anteroposterior axes. These findings provide an approach for the generation of AFE derivatives.

When differentiated in the presence of activin A in serum-free conditions, mouse embryonic stem cells efficiently generate an endoderm progenitor population defined by the coexpression of either Brachyury, Foxa2 and c-Kit, or c-Kit and Cxcr4. Specification of these progenitors with bone morphogenetic protein-4 in combination with basic fibroblast growth factor and activin A results in the development of hepatic populations highly enriched (45-70%) for cells that express the alpha-fetoprotein and albumin proteins. These cells also express transcripts of Afp, Alb1, Tat, Cps1, Cyp7a1 and Cyp3a11; they secrete albumin, store glycogen, show ultrastructural characteristics of mature hepatocytes, and are able to integrate into and proliferate in injured livers in vivo and mature into hepatocytes expressing dipeptidyl peptidase IV or fumarylacetoacetate hydrolase. Together, these findings establish a developmental pathway in embryonic stem cell differentiation cultures that leads to efficient generation of cells with an immature hepatocytic phenotype.

The liver is a central regulator of metabolism, and liver failure thus constitutes a major health burden. Understanding how this complex organ develops during embryogenesis will yield insights into how liver regeneration can be promoted and how functional liver replacement tissue can be engineered. Recent studies of animal models have identified key signaling pathways and complex tissue interactions that progressively generate liver progenitor cells, differentiated lineages and functional tissues. In addition, progress in understanding how these cells interact, and how transcriptional and signaling programs precisely coordinate liver development, has begun to elucidate the molecular mechanisms underlying this complexity. Here, we review the lineage relationships, signaling pathways and transcriptional programs that orchestrate hepatogenesis.

Mammary epithelial cells are embedded in a unique extracellular environment to which adipocytes and other stromal cells contribute. Mammary epithelial cells are critically dependent on this milieu for survival. However, it remains unknown which adipocyte-secreted factors are required for the survival of the mammary epithelia and what role these adipokines play in the process of ductal carcinoma tumorigenesis. Here, we take a systematic molecular approach to investigate the multiple ways adipocytes and adipokines can uniquely influence the characteristics and phenotypic behavior of malignant breast ductal epithelial cells. Microarray analysis and luciferase reporter assays indicate that adipokines specifically induce several transcriptional programs involved in promoting tumorigenesis, including increased cell proliferation (IGF2, FOS, JUN, cyclin D1), invasive potential (MMP1, ATF3), survival (A20, NFjB), and angiogenesis. One of the key changes in the transformed ductal epithelial cells associated with the cell cycle involves the induction of NFjB (five-fold) and cyclin D1 (three-fold). We show that by regulating the transcription of these molecules, the synergistic activity of adipocyte-derived factors can potentiate MCF-7 cell proliferation. Furthermore, compared to other stromal cell-secreted factors, the full complement of adipokines shows an unparalleled ability to promote increased cell motility, migration, and the capacity for angiogenesis. Adipocyte-secreted factors can affect tumorigenesis by increasing the stabilization of pro-oncogenic factors such as b-catenin and CDK6 as a result of a reduction in the gene expression of their inhibitors (i.e. p18). An in vivo coinjection system using 3T3-L1 adipocytes and SUM159PT cells effectively recapitulates the host-tumor interactions in primary tumors. Type VI collagen, a soluble extracellular matrix protein abundantly expressed in adipocytes, is further upregulated in adipocytes during tumorigenesis. It promotes GSK3b phosphorylation, b-catenin stabilization, and increased b-catenin activity in breast cancer cells and may critically contribute towards tumorigenesis when not counterbalanced by other factors.

Development of the ductal network in the mammary gland is dependent in part on the presence of macrophages. Here we utilize multi-photon microscopy and second harmonic generation to describe terminal end bud 3-dimensional structure and the organization of the surrounding collagen matrix. We have applied this approach to analyze the effect of macrophage deficiency on terminal end bud structure and collagen organization, using mice homozygous for a null mutation in the colony stimulating factor-1 gene (Csf1 op /Csf1 op ). Primary terminal end buds have an oblong shape, with long collagen I fibers close to the neck of the terminal end bud and radiating upwards in the direction of growth. Around the terminal end buds, the amount of total collagen I detected by antibody staining was not affected by macrophage deficiency. However the amount of collagen I organized into long fibers, detected by second harmonic generation signal, was reduced in Csf1 op /Csf1 op mice. Macrophage deficiency also caused terminal end buds to be rounder and shorter. These studies reveal a role for macrophages in collagen fibrillogenesis and in organization of the structure of terminal end buds. Developmental Dynamics 235:3222-3229, 2006.

155CSF-1 = colony-stimulating factor 1 or macrophage-colony-stimulating factor; CSF-1R = colony-stimulating-factor-1 receptor; IL = interleukin; MEC = mammary enriched chemokine; MMTV = mouse mammary tumor virus; RANK(-L) = receptor activator of nuclear factor κB (ligand); TEB = terminal end bud; TNF = tumor necrosis factor. Available online http://breast-cancer-research.com/content/4/4/155 IntroductionIt is well established that epithelial/mesenchymal interactions are important for postnatal development of the mammary ductal tree and its differentiation during pregnancy into a milk-producing structure [1]. The mesenchyme contains a heterogeneous group of cells [2] and several of these, such as fat cells and fibroblasts, are capable of producing factors that can promote the growth of epithelial cells [3][4][5][6]. This review focuses on the role of two types of migrant hematopoietic cells, macrophages and eosinophils, that have been recently found to accumulate extensively around terminal end buds (TEBs) during the pubertal burst of ductal growth [7]. Their chemoattractant factors and their roles in mammary cancer are also discussed. Leukocyte homing to the mammary gland AbstractEpithelial/mesenchymal cell interactions are necessary for proper ductal morphogenesis throughout all stages of mammary gland development. Besides the well-established stromal components, such as adipocytes and fibroblasts, the mammary stroma is also infiltrated with migrating blood cells, mostly macrophages and eosinophils. The focus of this review is on the role of macrophages and their growth factor colony-stimulating factor 1 (CSF-1) in promoting branching morphogenesis during postnatal mammary gland development through to lactation. The more restricted role of eosinophils and their chemoattractant eotaxin during pubertal ductal morphogenesis is also discussed. A possible interaction between macrophages and eosinophils in ductal morphogenesis is considered, along with the roles of other chemokines. This role of macrophages in normal development also appears to be subverted by tumors of the mammary gland to promote the escape of the tumor cells from the local environment and enhance their rate of metastasis. These data emphasize the dual role of macrophages in the promotion of epithelial growth in normal and cancer states.

Macrophages play an important role in organ development, tissue homeostasis, and remodeling. Thus, we monitored the presence of F4/80-positive macrophages in the pancreas of wild-type mice, and some developmental features of this complex tissue were compared throughout life in wild-type and macrophage-deficient Csf1op/Csf1op (op/op) mice. The combined use of immunohistochemistry, morphometry, and cell quantification allows us to evaluate insulin and glucagon cell mass, total and insulin cell proliferation, and apoptosis in fetuses (E18.5), weanings (postnatal day 21), nonpregnant adults, and adults in late pregnancy (18.5 days). F4/80-positive macrophages were found in pancreases recovered from Csf1op/Csf1+ (op/+) mice but were extremely scarce or absent in pancreas recovered from op/op ones at all studied time-points. The macrophage-deficient op/op phenotype was clearly associated with a major insulin mass deficit in fetuses and adults, abnormal postnatal islet morphogenesis, and impaired pancreatic cell proliferation at weaning and late pregnancy. We also obtained indirect evidence of increased neogenesis in this model at time-points when pancreatic remodeling does occur. The demonstration of the colony-stimulating factor 1-dependent macrophage involvement in life-time pancreas development/remodeling allows us to pinpoint the tissue-modeling and remodeling functions of this leukocyte lineage.

The recent identification of progenitor populations that contribute to the developing heart in a distinct spatial and temporal manner has fundamentally improved our understanding of cardiac development. However, the mechanisms that direct atrial versus ventricular specification remain largely unknown. Here we report the identification of a progenitor population that gives rise primarily to cardiovascular cells of the ventricles and only to few atrial cells (<5%) of the differentiated heart. These progenitors are specified during gastrulation, when they transiently express Foxa2, a gene not previously implicated in cardiac development. Importantly, Foxa2+ cells contribute to previously identified progenitor populations in a defined pattern and ratio. Lastly, we describe an analogous Foxa2+ population during differentiation of embryonic stem cells. Together, these findings provide insight into the developmental origin of ventricular and atrial cells, and may lead to the establishment of new strategies for generating chamber-specific cell types from pluripotent stem cells.