Cell fusion and some subcellular properties of heterokaryons and hybrids

Spontaneous Fusion with Transformed Mesenchymal Stromal Cells Results in Complete Heterogeneity in Prostate Cancer Cells

Tumor cells gain advantages in growth and survival by acquiring genotypic and phenotypic heterogeneity. Interactions with bystander cells in the tumor microenvironment contribute to the progression of heterogeneity. We have shown that fusion between tumor and bystander cells is one form of interaction, and that tumor-bystander cell fusion has contrasting effects. By trapping fusion hybrids in the heterokaryon or synkaryon state, tumor-bystander cell fusion prevents the progression of heterogeneity. However, if trapping fails, fusion hybrids will resume replication to form derivative clones with diverse genomic makeups and behavioral phenotypes. To determine the characteristics of bystander cells that influence the fate of fusion hybrids, we co-cultured prostate mesenchymal stromal cell lines and their spontaneously transformed sublines with LNCaP as well as HPE-15 prostate cancer cells. Subclones derived from cancer-stromal fusion hybrids were examined for genotypic and phenotypic diversifications. Both stromal cell lines were capable of fusing with cancer cells, but only fusion hybrids with the transformed stromal subline generated large numbers of derivative subclones. Each subclone had distinct cell morphologies and growth behaviors and was detected with complete genomic hybridization. The health conditions of the bystander cell compartment play a crucial role in the progression of tumor cell heterogeneity.

LUCA to LECA, the Lucacene: A model for the gigayear delay from the first prokaryote to eukaryogenesis

It is puzzling why life on Earth consisted of prokaryotes for up to 2.5 ± 0.5 billion years (Gy) before the appearance of the first eukaryotes. This period, from LUCA (Last Universal Common Ancestor) to LECA (Last Eucaryotic Common Ancestor), we have named the Lucacene, to suggest all prokaryotic descendants of LUCA before the appearance of LECA. Here we present a simple model based on horizontal gene transfer (HGT). It is the process of HGT from Bacteria to Archaea and its reverse that we wish to simulate and estimate its duration until eukaryogenesis. Rough quantitation of its parameters shows that the model may explain the long duration of the Lucacene.

Cancer cell's neuroendocrine feature can be acquired through cell-cell fusion during cancer-neural stem cell interaction

Advanced and therapy-resistant prostate tumors often display neural or neuroendocrine behavior. We assessed the consequences of prostate cancer cell interaction with neural cells, which are rich in the human prostate and resident of the prostate tumor. In 3-dimensional co-culture with neurospheres, red fluorescent human LNCaP cells formed agglomerates on the neurosphere surface. Upon induced neural differentiation, some red fluorescent cells showed morphology of fully differentiated neural cells, indicating fusion between the cancer and neural stem cells. These fusion hybrids survived for extended times in a quiescent state. A few eventually restarted cell division and propagated to form derivative hybrid progenies. Clones of the hybrid progenies were highly heterogeneous; most had lost prostatic and epithelial markers while some had acquired neural marker expression. These results indicate that cancer cells can fuse with bystander neural cells in the tumor microenvironment; and cancer cell fusion is a direct route to tumor cell heterogeneity.

Triggered Cell-Cell Fusion Assay for Cytoplasmic and Organelle Intermixing Studies

Different multicellular organisms undergo cell-cell fusion to form functional syncytia that support specialized functions necessary for proper development and survival. For years, monitoring the structural consequences of this process using live-cell imaging has been challenging due to the unpredictable timing of cell fusion events in tissue systems. Here we present a triggered vesicular stomatitis virus G-protein (VSV-G)-mediated cell-cell fusion assay that can be used to synchronize fusion between cells. This allows the study of cellular changes that occur during cell fusion. The process is induced using a fast wash of low pH isotonic buffer, promoting the fusion of plasma membranes of two or more adjacent cells within seconds. This approach is suitable for studying mixing of small cytoplasmic molecules between fusing cells as well as changes in organelle distribution and dynamics. © 2018 by John Wiley & Sons, Inc.

Growth of epithelium from a preneoplastic mammary outgrowth in response to mammary adipose tissue

We investigated the effects of conditioned media derived from mouse mammary fat pads on the proliferation of CL-S1 cells, an epithelial cell line originally isolated from a preneoplastic mammary outgrowth line. Cell proliferation in vitro in serum-free defined medium was compared to that in this medium conditioned using intact mammary fat pad pieces or isolated fat pad adipocytes. Culture medium was conditioned by incubating the conditioning material in defined culture medium for 24 h at 37 degrees C. Conditioned medium induced CL-S1 proliferation as much as 10- to 20-fold above the minimal levels of growth in control cultures after 13 d of culture. The growth-stimulatory factor(s) had an apparent molecular weight of greater than 10 kDa. This growth-stimulatory activity was both heat and trypsin stable. Because the role of adipose tissue is to store and release lipids, we next tested whether lipids are released during medium conditioning. The lipid composition of the fat pad conditioned medium was characterized using both thin layer and gas liquid chromatography. These lipid analyses indicated that the fat pad pieces released significant amounts of fatty acids and phospholipids into the medium during the conditioning period. The free fatty acid composition included both saturated and unsaturated molecules, and about 80% of the total fatty acids consisted of palmitate, stearate, oleate, and linoleate. These same fatty acids were a structural component of the majority of phospholipid found in the medium. The addition of palmitate or stearate to defined medium had no effect or was inhibitory for CL-S1 proliferation, depending on the concentration used. Defined medium supplemented with oleate, arachidonate, or linoleate induced CL-S1 proliferation, and the inhibitory effects of palmitate and stearate were overcome by addition of oleate and linoleate. These data indicate that both unsaturated and saturated fatty acids are released from intact adipose cells of the mouse mammary fat pad and that fatty acids can influence the growth of preneoplastic mouse mammary epithelium. Thus, unsaturated fatty acids, perhaps in conjunction with other substances released simultaneously, are candidate molecules for the substances that mediate the effect of adipose tissue on growth of epithelium.

Genome intermixing and sister chromatid exchange in newly-formed HeLa-3T3 Hybrid cells

Mouse and human genomes occupy distinct regions within hybrid interphase nuclei following division of HeLa-3T3 heterokaryons. With subsequent cell division the proportion of interphase cells displaying separation of human and mouse genomes decreases. Examination of several hundred hybrid colonies revealed a linear relation between the log of the fraction of interphase cells with separated genomes and the log of clone size. This indicates that there is a constant probability that separated genomes will intermingle at each mitosis. Human and mouse chromosomes can also occupy distinct sectors in metaphase spreads derived from heterokaryons. Computer analysis of the distribution of chromosomes within 548 hybrid metaphases showed that mouse and human chromosomes are randomly intermixed within several divisions and before the onset of rapid chromosome loss. Sister chromatid exchange (SCE) rates were also measured in mass populations of newly-formed HeLa-3T3 hybrid cells. For most hybrid metaphases there was not significant change in SCE rates within the human chromosome set. In a small minority of hybrid metaphases, characterized by asynchronous condensation of chromosome sets, there was a 50-fold increase in SCE. However, chromosomes are progressively lost from all hybrid cells. Thus, the two processes examined in the present studies, the distribution of human chromosomes at metaphase and SCE, are not implicated in the preferential loss of human chromosomes from HeLa-3T3 cells.

Macrophage polykarya

Multinucleated giant cells are commonly found in a wide variety of inflammatory reactions. They are formed at sites of tissue injury by fusion of freshly exuded monocytes, the rate of fusion being dependent on a range of extracellular and intracellular factors. Electron miscroscopy shows that the pooled components of the fused monocytes are not randomly dispersed in the syncytium, but are highly reorganized into a functioning unit. In addition, histochemical and biochemical profiles of cell populations containing these polykarya display a range of metabolic activities, including DNA synthesis, which, on occasions, is followed by successful mitotic division and the formation of polyploid daughter cells. Fusion results in the loss of some surface receptors which in turn interferes with the phagocytic performance of polykarya, which is generally less pronounced than their mononuclear precurses. In addition, polykarya are not as actively motile as macrophages although phenomena of contact inhibition are less obvious. On the other hand, the multinucleate giant cells display prominent exocytosis which may aid in the degradation of extracellular material. The properties of macrophage polykarya contrast with macrophage homokarya produced in vitro. The latter are actively phagocytic, do not synthesize DNA, and have a longer half-life than the syncytia produced in chronic inflammatory reactions. It may well be that the polykarya in such reactions are not true homokarya.

A comparison of cAMP phosphodiesterases in normal, malignant, and somatic cell hybrids

Hybrids (PCM) between a malignant mouse lymphoma suspension cell line (P388F-36) and a normal Chinese hamster fibroblastic cell line (Ch23) have already been isolated in this laboratory. Investigations were carried out on the cAMP phospodiesterases of the parents and two of these hybrids--PCM2 and PCM3. PCM3 shows a rather unusual growth characteristic in that a considerable proportion of the cells exist at any one time either in suspension or only loosely attached to the substratum, the remaining cell population existing in a monolayer form. It was found that each cell line exhibited multiple forms of the enzyme with varying affinities for cAMP. Both parents, although different, contained high-, low-, and extra-high apparent Km forms of the enzyme. The hybrids exhibited characteristics of both parental systems but were different from each other. Neither hybrid exhibited a high-Km enzyme, but both exhibited two low-Km forms. There was also a slight variation between monolayer and suspension cells of PCM3 hybrid. An attempt has been made to explain these phenomena with respect to hybridization and the growth characteristics of the cells.

Membrane ultrastructural changes during calcium phosphate-induced fusion of human erythrocyte ghosts

Nascent calcium phosphate promotes the agglutination and fusion of human erythrocyte ghosts. Membrane phospholipids of erythrocyte ghosts treated with Ca2+ and phosphate ions become exposed to attack by phospholipase C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3) (Bacillus cereus). Freeze-fracture pictures of fused erythrocyte ghosts show the presence of regions deficient in intramemebrane particles in the protoplasmic face which we believe to be regions of fusion. Discontinuous regions of the protoplasmic and exoplasmic faces are observed, which are apparently intermediate stages in the process of fusion. TH-in-section electron micrographs reveal deposits of calcium phosphate in areas of contact and fusion of ghosts. Ca2+ in the presence of N-[tris(hydroxymethyl)methyl]glycine (Tricine) buffer causes the formation of blebs in the membrane but does not cause changes in the intramembrane particle pattern or induce fusion. It is suggested that nascent calcium phosphate acts by forming protein-free regions of phospholipid bilayer which can fuse readily.

Human lymphocyte-mouse myeloma somatic cell hybrids: selective hybrid formation

Fusion of unfractionated human lymphocytes with mouse myeloma cells resulted in proliferating hybrid colonies, almost all producting human Ig. We examined whether this high frequency of Ig production was the result of selective formation of human B lymphocyte-mouse myeloma hybrids, rather than induction of Ig genes in T lymphocytes. Unfractionated peripheral lymphocytes and B lymphocytes from patients with the common variable form of agammaglobulinemia formed proliferating somatic cell hybrid colonies. In contrast, peripheral lymphocytes from a patient with agammaglobulinema who lacked B lymphocytes, as well as albumin gradient fractions of peripheral blood which do not contain B lymphocytes, failed to produce somatic cell hybrids with three different myeloma parent cell lines. B, T, and precursor lymphocytes all had Sendai virus receptors, as witnessed by viral agglutination. We conclude that fusion of human lymphocytes with mouse myeloma cells results in selective hybrid formation, rather than activation of Ig genes in disparate cell types. Only B lymphocyte-mouse myeloma heterokaryons form hybrid cells.

Electron microscope assessment of fertilization of rabbit ova treated with concanavalin A and wheat germ agglutinin

Zonaless rabbit ova, exposed to Concanavalin A or Wheat Germ Agglutinin, then to uterine capacitated sperm produce pronuclear, 2 and 4 stage embryos that are indistinguishable from controls. Absence of cortical granules indicates that the ova were fertilized and not merely activated. Survival of lectin-bearing receptors during the period necessary for fertilization was evaluated in ova marked with ferritin-conjugated lectin.

Failure of XX cells containing the sex reversed gene to produce gametes in allophenic mice

Allophenic mice have been produced by combining embryos from normal albino mice with embryos of normally pigmented mice carrying the autosomal dominent gene for sex reversed (Sxr) in order to determine the ability of XXSxr cells to differentiate either into sperm or eggs. Sixteen male and six female allophenes have thus far produced more than 1,200 offspring, none of which arose from an XXSxr primordial germ cell. Two allophenic mice were sterile hermaphrodites, and 13 others have yet to be tested. These results indicated that an XX cell is incapable of spermatogenesis even when supplied with the male determining Sxr gene, and that this gene also prevents XX cells from undergoing oogenesis. The latter result contrasts with a previous report of a functional sex reversed oocyte in the mouse.