Primary culture of mouse mammary tumor epithelial cells embedded in collagen gels

Rebooting the collagen gel: Artificial hydrogels for the study of epithelial mesenchymal transformation

The collagen gel has been used to study epithelial-mesenchymal transformation (EMT) for over 30 years. With advances in the field of materials sciences, new options are available to design optically clear, three-dimensional nature-inspired matrix mimetics to study EMT. Here, we review the history of the collagen gel assay, discuss its current use and how newer artificial matrices can be built to simulate in vivo extracellular environments and investigate important current questions in the EMT field. We suggest that further collaborations between materials scientists and biologists will be critical to move the field of EMT forward. Developmental Dynamics 247:332-339, 2018. © 2017 Wiley Periodicals, Inc.

Live births from isolated primary/early secondary follicles following a multistep culture without organ culture in mice

Although the ovary has a large store of germ cells, most of them do not reach mature stages. If a culture system could be developed from early growing follicles to mature oocytes, it would be useful for biological research as well as for reproductive medicine. This study was conducted to establish a multistep culture system from isolated early growing follicles to mature oocytes using a mouse model. Early growing follicles with diameters of 60-95 μm corresponding to primary and early secondary follicles were isolated from 6-day-old mice and classified into three groups by diameter. These follicles contained oocytes with diameters of ~45 μm and one or a few layered granulosa cells on the basal lamina. Embedding in collagen gel was followed by first-step culture. After 9-day culture, the growing follicles were transferred onto collagen-coated membrane in the second step. At day 17 of the culture series, the oocyte-granulosa cell complexes were subjected to in vitro maturation. Around 90% of the oocytes in follicles surviving at day 17 resumed second meiosis (metaphase II oocytes: 49.0-58.7%), regardless of the size when the follicle culture started. To assess developmental competence to live birth, the eggs were used for IVF and implantation in pseudopregnant mice. We successfully obtained two live offspring that produced next generations after puberty. We thus conclude that the culture system reported here was able to induce the growth of small follicles and the resultant mature oocytes were able to develop into normal mice.

Postnatal mammary gland morphogenesis

Mammary glands develop postnatally by branching morphogenesis creating an arborated ductal system on which secretory lobuloalveoli develop at pregnancy. This review focuses on the interrelated questions of how ductal and alveolar morphogenesis and growth are regulated in the mouse mammary gland and covers progress made over approximately the last decade. After a brief overview of glandular development, advances in understanding basic structural questions concerning mechanisms of duct assembly, elongation, and bifurcation are considered. Turning to growth regulation, remarkable progress has taken place based largely on the study of genetically engineered mice that lack or overexpress a single gene. The use of mammary glands from these and wildtype animals in sophisticated epithelial-stromal or epithelial-epithelial recombination experiments are reviewed and demonstrate paracrine mechanisms of action for the classical endocrine mammogens, estrogen, progesterone, growth hormone, and prolactin. In addition, IGF-1, EGF, or related peptides, and elements of the activin/inhibin family, were shown to be necessary for ductal growth. The inhibition of ductal growth, and in particular, lateral branching, is necessary to preserve stromal space for later lobuloalveolar development. Excellent evidence that TGF-beta1 naturally inhibits this infilling, possibly by blocking hepatocyte growth factor synthesis, is reviewed along with evidence indicating that the action of TGF-beta1 is modulated by its association with the extracellular matrix. Finally, experimental approaches that may help integrate the wealth of new findings are discussed.

Investigation of mouse mammary ductal growth regulation using slow-release plastic implants

Mammary ductal development in the mouse is now thought to depend on an interplay of locally produced (glandular) and systemic mammogens. A novel plastic implant material, ethylene vinyl acetate copolymer (Elvax 40P), capable of the slow-release of undenatured, bioactive molecules in situ, now enables treatment of small regions of the mammary gland for extended periods with hormones and growth factors. Here we describe results obtainable with this technique. Specifically, the classical mammogens, estrogen, growth hormone, and prolactin, as well as the nontraditional mammogens, epidermal growth factor and cholera toxin, were shown to stimulate ductal growth in zones around an implant in ovariectomized animals. The possibility that these observations reflect the existence of multiple mammogenic pathways is discussed.

The interaction of melanoma cells with fibroblasts and endothelial cells in three-dimensional macromolecular matrices: a model for tumour cell invasion

Comparative quantitative data are presented concerning the adhesion, proliferation and invasive behaviour of RPMI-3460 melanoma cells on (1) plain collagen gels, (2) monolayer cultures of fibroblasts and endothelial cells growing on the gel surface, and (3) the exposed endothelial and fibroblast extracellular matrices (ECMs). Both types of ECMs enhanced melanoma cell adhesion and proliferation (compared with plain gels) and had marked, but distinctive, effects on melanoma morphology. The thickness and composition of the ECMs was altered by treatment of the matrices with enzymes (trypsin, elastase and chondroitinase ABC) or by using ECMs produced by endothelial cells at various times after confluence. Variations in the thickness and composition of the ECMs had no effect on the behaviour of melanoma cells growing on these matrices; our results suggest that the glycoproteins and glycosaminoglycan ECM constituents removed by digestion with the enzymes do not play an important role in melanoma cell attachment, proliferation and migration. Melanoma cells plated on the surface of a plain collagen gel rapidly migrated down into the collagen matrix, with approximately 30% of the cells found within the gel after 6 days of incubation. Fibroblast and endothelial ECMs significantly and distinctively inhibited melanoma invasion into the underlying collagen gel. The extensive invasion of melanoma cells into the gel was not accompanied by hydrolysis of the collagen fibres. Conversely, fibroblast and endothelial ECMs, which acted as effective barriers, were extensively hydrolysed by the melanoma cells. The possible use of ECMs deposited on collagen in the study of melanoma local invasion (on fibroblast ECMs) and extravasation (on endothelial ECMs) is discussed.

Similar growth pattern of mouse mammary epithelium cultivated in collagen matrix in vivo and in vitro

Mouse mammary ductal cells cultured in type I collagen gels give rise to three-dimensional multicellular outgrowths consisting of thin spikes which are often branched, and which may have pointed or blunt ends. The significance of these spikes to normal ductal morphogenesis has been unclear, since identical structures are not known to occur in vivo; conversely, it has not been possible to maintain in gel culture the highly structured end buds which are characteristic of ductal elongation in the animal. In order to evaluate whether the pattern of radiating spikes observed in collagen gel cultures results from chemical or physical peculiarities of the culture environment, a small volume of unpolymerized type I collagen solution was injected into mammary gland-free fat pads of young adult mice. After the bubble of collagen had polymerized, an implant of mammary ductal epithelium was introduced into the center of the gel. Histological examination of the implants after 3 to 6 days of growth revealed numerous small epithelial spikes, similar to those observed in gel culture, extending into the fibrous matrix. The early stages of regeneration of mammary implants placed in gland-free fat pads were then examined without the addition of exogenous collagen. In cases where the epithelium happened to contact a fibrous region of the fatty stroma, spikes were also seen to form in these natural collagenous substrates. Whether or not exogenous collagen was used, normal end buds were formed only when epithelial spikes contacted adipocytes. It was concluded that the three-dimensional pattern of radiating tubules in collagen gels in vitro is not merely an artifact of culture, but has a counterpart in vivo whereever regenerating mammary epithelium is surrounded by fibrous stroma. A model is presented in which the pattern of epithelial outgrowth is determined by the physical characteristics of the surrounding stroma; in collagen matrix a comparatively primitive and unspecialized type of morphogenesis occurs which may not require the participation of stromal cells. In contrast, epithelial-adipocyte interactions appear to be necessary for the formation of end buds and subsequent morphogenesis of fully structured mammary ducts.

Growth effect of lithium on mouse mammary epithelial cells in serum-free collagen gel culture

The effect of lithium on the growth of mammary epithelial cells from adult virgin and midpregnant BALB/c or BALB/cfC3H mice was tested in a serum-free collagen gel culture system. The serum-free medium consisted of a 1:1 mixture of Ham's F12 and Dulbecco's Modified Eagle's medium supplemented with insulin, transferrin, cholera toxin, epidermal growth factor (EGF), and bovine serum albumin fraction V (BSA V). A multifold increase in cell number occurred during 10-12 days of culture in this medium. In dose-response studies in which the concentration of each component of this serum-free medium was varied in turn, the addition of LiCL (10 mM) enhanced growth at most concentrations of each factor. However, LiCl could not enhance growth in the absence of insulin or BSA V, but could replace EGF. The optimal concentration of LiCl was 5-10 mM; higher concentrations (20-80 mM) were toxic. KCl (1-10 mM) when added to the serum-free medium slightly stimulated growth; the addition of NaCl to the medium had little effect on growth. LiCl did not enhance the growth of cells from spontaneous mammary tumors of BALB/cfC3H mice.

Growth of mammary epithelial cells from neonatally sex hormone-exposed mice in serum-free collagen gel culture

Neonatal sex hormone treatments are known to cause an increase in mammary tumors in female mice with expressed mammary tumor virus (MTV). The growth of mammary epithelial cells from mice treated neonatally with sex hormones was studied in response to growth-stimulatory factors in a serum-free collagen gel culture system which sustains the growth of normal mammary epithelial cells. Animals were treated with hormones or oil-vehicle for the first 5 days after birth. Cells from control mice at 2 and 3 months of age showed a maximal growth response to insulin at 5-10 micrograms/ml and LiCl at 5-20 mM. Cells responded to epidermal growth factor at all concentrations used (1, 10 and 50 ng/ml). In contrast, mammary epithelial cells from mice treated neonatally with estrogen (estradiol and diethylstilbestrol (DES] showed a reduced growth response to the growth factors tested.

The culture of chick embryo mesoderm cells in hydrated collagen gels

Chick embryo mesoderm cells are various stages of differentiation were cultured in three-dimensional matrices of hydrated collagen. The tissues used were: stage 5 mesoderm from regions adjacent to the primitive streak; stage 12 mesoderm, comprising somitic, unsegmented (segmental plate) and lateral plate mesoderm; and stage 18 sclerotome. Explants were examined by phase contrast microscopy, including time-lapse, and scanning and transmission electron microscopy. The cells showed an increased ability to adhere to, and move in, the collagen gel with advancing stage. Of the stage 12 tissues, the unsegmented mesoderm was initially the slowest to grow out of the explant. Sclerotome cells showed by far the greatest ability to move within the gel. Where the collagen fibrils were randomly oriented, the cell morphology was polypodial and advancing lamellipodia showed clear undulations at their leading edges. A distinction was drawn between these undulations and the classical major ruffles which are seen in two-dimensional culture to uplift and pass back along the cell surface. The latter were not seen in the collagen matrix and were presumably suppressed by the three-dimensional culture configuration while the leading edge undulations were not. Ultrastructural examination showed that the cells possessed patches of amorphous material on their surface, which was sometimes interposed between the plasma membrane and collagen fibrils. Addition of hyaluronic acid (2 mg/ml) had an effect only the segmented mesoderm, where outgrowth was enhanced. Although the addition of plasma fibronectin (50 micrograms/ml) to the cultures did not affect any of the tissues, the removal of this substance, by antifibronectin antiserum or by the use of fibronectin depleted serum, inhibited outgrowth in most cases. The only tissue not reproducibly inhibited in this way was sclerotome. Alignment of the collagen fibres by the explants was observed, accompanied by an elongation of the outgrowing cells which, in bipolar form, preferentially moved up and down the aligned tracts. Scanning electron microscopy suggested that cell processes attached to, and presumably exerted tension on, bundles of fibrils thereby pulling them into line. Cell-to-cell contact was not accompanied by contact paralysis as judged by time-lapse micrography.

Lymphocyte migration into three-dimensional collagen matrices: a quantitative study

Lymphocytes have been plated onto the surface of three-dimensional gels of native collagen fibers, and their distribution throughout the three-dimensional collagen matrix has been determined in a quantitative fashion at various times thereafter. Information regarding the total number of applied cells may be obtained by this means. Lymphocyte penetration into the collagen gel does not appear to involve the expression of collagenolytic activity, nor does it require the presence of serum. Analysis of the kinetics of lymphocyte penetration into the gel matrix indicates that lymphocytes are migrating in a "random-walk" fashion. Our objective has been to establish a model system for studying the cell-matrix and cell-cell interactions which influence the pattern of lymphocyte recirculation in vivo and the results presented here are discussed in this context.