Contact-mediated myogenesis and increased acetylcholinesterase activity in primary cultures of mouse teratocarcinoma cells

The multiple biological roles of the cholinesterases

It is tacitly assumed that the biological role of acetylcholinesterase is termination of synaptic transmission at cholinergic synapses. However, together with its structural homolog, butyrylcholinesterase, it is widely distributed both within and outside the nervous system, and, in many cases, the role of both enzymes remains obscure. The transient appearance of the cholinesterases in embryonic tissues is especially enigmatic. The two enzymes' extra-synaptic roles, which are known as 'non-classical' roles, are the topic of this review. Strong evidence has been presented that AChE and BChE play morphogenetic roles in a variety of eukaryotic systems, and they do so either by acting as adhesion proteins, or as trophic factors. As trophic factors, one mode of action is to directly regulate morphogenesis, such as neurite outgrowth, by poorly understood mechanisms. The other mode is by regulating levels of acetylcholine, which acts as the direct trophic factor. Alternate substrates have been sought for the cholinesterases. Quite recently, it was shown that levels of the aggression hormone, ghrelin, which also controls appetite, are regulated by butyrylcholinesterase. The rapid hydrolysis of acetylcholine by acetylcholinesterase generates high local proton concentrations. The possible biophysical and biological consequences of this effect are discussed. The biological significance of the acetylcholinesterases secreted by parasitic nematodes is reviewed, and, finally, the involvement of acetylcholinesterase in apoptosis is considered.

Acetylcholinesterase involvement in apoptosis

To date, more than 40 different types of cells from primary cultures or cell lines have shown AChE expression during apoptosis and after the induction apoptosis by different stimuli. It has been well-established that increased AChE expression or activity is detected in apoptotic cells after apoptotic stimuli in vitro and in vivo, and AChE could be therefore used as a marker of apoptosis. AChE is not an apoptosis initiator, but the cells in which AChE is overexpressed undergo apoptosis more easily than controls. Interestingly, cells with downregulated levels of AChE are not sensitive to apoptosis induction and AChE deficiency can protect against apoptosis. Some tumor cells do not express AChE, but when AChE is introduced into a tumor cell, the cells cease to proliferate and undergo apoptosis more readily. Therefore, AChE can be classified as a tumor suppressor gene. AChE plays a pivotal role in apoptosome formation, and silencing of the AChE gene prevents caspase-9 activation, with consequent decreased cell viability, nuclear condensation, and poly (adenosine diphosphate-ribose) polymerase cleavage. AChE is translocated into the nucleus, which may be an important event during apoptosis. Several questions still need to be addressed, and further studies that address the non-classical function of AChE in apoptosis are needed.

Stem cells: The therapeutic role in the treatment of diabetes mellitus

The unlimited proliferative ability and plasticity to generate other cell types ensures that stem cells represent a dynamic system apposite for the identification of new molecular targets and the production and development of novel drugs. These cell lines derived from embryos could be used as a model for the study of basic and applied aspects in medical therapeutics, environmental mutagenesis and disease management. As a consequence, these can be tested for safety or to predict or anticipate potential toxicity in humans. Human ES cell lines may, therefore, prove clinically relevant to the development of safer and more effective drugs for patients presenting with diabetes mellitus.

Embryonic stem cells: prospects for developmental biology and cell therapy

Stem cells represent natural units of embryonic development and tissue regeneration. Embryonic stem (ES) cells, in particular, possess a nearly unlimited self-renewal capacity and developmental potential to differentiate into virtually any cell type of an organism. Mouse ES cells, which are established as permanent cell lines from early embryos, can be regarded as a versatile biological system that has led to major advances in cell and developmental biology. Human ES cell lines, which have recently been derived, may additionally serve as an unlimited source of cells for regenerative medicine. Before therapeutic applications can be realized, important problems must be resolved. Ethical issues surround the derivation of human ES cells from in vitro fertilized blastocysts. Current techniques for directed differentiation into somatic cell populations remain inefficient and yield heterogeneous cell populations. Transplanted ES cell progeny may not function normally in organs, might retain tumorigenic potential, and could be rejected immunologically. The number of human ES cell lines available for research may also be insufficient to adequately determine their therapeutic potential. Recent molecular and cellular advances with mouse ES cells, however, portend the successful use of these cells in therapeutics. This review therefore focuses both on mouse and human ES cells with respect to in vitro propagation and differentiation as well as their use in basic cell and developmental biology and toxicology and presents prospects for human ES cells in tissue regeneration and transplantation.

The neurula stage mouse embryo in control of neuroblastoma

The purpose of this study was to determine whether the neurula stage mouse embryo can regulate tumor formation of C-1300-3 neuroblastoma cells. Five neuroblastoma cells were injected into the second somite of neurula stage embryos, and their ability to form tumors was tested, 24 hr later, by transplanting the portion of the embryo containing the cancer cells into the testes of adult mice. Only one-third the number of tumors was obtained in comparison with controls in which (i) five neuroblastoma cells were injected into blocks of liver tissue that were then transplanted into the testes of adult animals or (ii) five C-1300-3 neuroblastoma cells were injected directly into the testes. When five C-1300-3 cells were injected into somites, which had been dissected from embryos, and the injected somites were placed in animals, significantly fewer tumors were obtained in relationship with controls. Although it is not known whether the neuroblastoma cells are induced to differentiate or are killed by the embryonic tissue, the effect appeared to be specific because the tumor-forming ability of L1210 leukemia, B-16 melanoma, embryonal carcinoma 247, and a parietal yolk sac carcinoma was unaffected by somites.

Isoenzyme studies of whole muscle grafts and movement of muscle precursor cells

Isoenzymes of glucose-6-phosphate isomerase (GPI: E.C. 5.3.1.9) were used as markers to determine the origin of cells which give rise to new muscle formed in allografts of whole intact muscle. GPI isoenzymes were also employed to see whether host precursor cells, which have been shown to contribute to muscle formation in grafts of minced muscle, can be derived from muscle lying adjacent to grafts. Excellent muscle regeneration was found in allografts of extensor digitorum longus (EDL) muscle examined after 58 days: 12 of 16 grafts contained 80% or more new muscle. Isoenzyme analysis showed that most, and in 2 instances all, new muscle was derived from implanted donor cells; however, there was strong evidence that in 5 grafts some, or all, new muscle must have resulted from host cells moving into the graft. Although hybrid isoenzyme was not detected this was attributed to factors associated with host tolerance which appear to interfere with fusion between host and donor myoblasts. Isografts of minced muscle were placed next to whole EDL muscle allografts to see if cells from allografts moved into adjacent regenerating tissue. Unfortunately, muscle regeneration in minced isografts was poor; only 3 contained 50% or more new muscle and most contained large amounts of fibrous connective tissue. Only a single isoenzyme band was detected in 11 isografts, but in five instances, the presence of a second band showed that cells from EDL allografts were also present. As no hybrid isoenzyme was detected, it is not known whether these cells which had moved into the regenerating minced grafts were muscle precursors, fibroblasts or some other cell types.

Differences in the cyclic AMP-dependent phosphorylation of plasma membrane proteins of differentiated and undifferentiated L6 myogenic cells

Differences in the cyclic AMP-dependent plasma membrane phosphorylation system of undifferentiated and differentiated L6 myogenic cells have been detected. Endogenous plasma membrane protein phosphorylation in undifferentiated L6 myoblasts was stimulated more than three fold by 5 x 10(-5) M cyclic AMP, whereas no statistically significant cyclic AMP-dependent phosphorylation of endogenous plasma membrane proteins was observed in differentiated L6 cells. In undifferentiated cells cyclic AMP promoted the phosphorylation of several proteins, the most prominent of which had a molecular weight of 110,000. In differentiated cells cyclic AMP did not selectively promote the phosphorylation of specific plasma membrane proteins. Both differentiated and undifferentiated L6 cells, however, contain a cyclic AMP-dependent protein kinase capable of catalyzing the phosphorylation of exogenous substrates, such as histone f2b. Therefore, the data show that differentiation in L6 cells is associated with a selective change in the activity of a plasma membrane cyclic AMP-dependent protein kinase which employs endogenous membrane proteins as substrate.

The characterization of SV40-transformed cell lines derived from mouse teratocarcinoma: growth properties and differentiated characteristics

Mouse teratocarcinoma cells derived from embryoid bodies of 129SVsl mice were cultured in vitro to permit their differentiation. These cells were then infected with simiam virus 40 (SV40) and 31 cloned cell lines (SVTER) were derived from these cultures. All 31 SVTER cell lines contained the SV40 tumor (T) antigen and grew as permanent lines in culture. Mock-infected embryoid body cultures did not give rise to permanent cell lines. The morphology of each SVTER cell line was distinct and did not change during successive subclonings. The growth properties and tumorigenic potential of all 31 SVTER cell lines were investigated. None of these lines produced tumors in 129SVsl mice. Each cell line was tested for its ability to (1) grow in medium containing 1% serum, (2) plate on cell monolayer, and (3) form clones in methocel suspension. Only three of the SVTER cell lines were transformed with respect to all three of these criteria. Most of these cell lines were minimal transformants. The SVTER cell lines were tested for creatine phospholinase (CPK), an enzyme activity chracteristic of mouse brain and muscle tissue, and the protease, plasminogen activator (PA) which is found in embryoid bodies and several differentiated cell types. Some of the SVTER cell lines contained high levels of CPK, while others had high levels of PA and a third group of cells contained neither enzyme activity. No SVTER cell line was found with high levels of both these enzyme activities. This result suggests that mutually exclusive sets of genes are expressed in these cells as might be expected from the distinct tissue distribution of the two enzyme activities studied. These SVTER cell lines may be useful in reconstructing developmental pathways of differentiating teratomas in vitro.

Biochemical markers of the progress of differentiation in cloned teratocarcinoma cell lines

The progeny of single teratocarcinoma cells will give rise to several different cell types in vitro, and the latter were shown to be functionally differentiated by biochemical criteria. In all these studies, cloned lines of mouse teratocarcinoma cells were assayed during the course of differentiation for some biochemical products characteristic of the tissues formed. The carcinoembryonic protein, alpha-foetoprotein, was not synthesized by undifferentiated embryonal carcinoma (EC) cells, but was synthesized in increasing amounts during their differentiation to endoderm-type cells in suspension culture. alpha-Foetoprotein was shown to be a product of endoderm cells, but not all endoderm cells synthesized this protein. During the course of further differentiation when EC cells or aggregates were grown in tissue-culture dishes, other biochemical products appeared. In cultures containing predominantly nerve-type cells, there was a 30-fold increase in the specific activity of acetylcholinesterase, with concomitant appearance of the aldolase isoenzyme characteristic of mouse brain. In some cultures, a small amount of muscle-type cell formation was marked by the appearance of the MB isoenzyme of creatine phosphokinase. Generally, biochemical differentiation was immature.

Intrathymic pathogenesis and dual genetic control of myasthenia gravis

We propose a two-step model for the pathogenesis of myasthenia gravis. In the first step, primitive intrathymic stem-cells are induced by abnormal stimuli to differentiate to (abnormal?) myogenic cells. In the second step, immunocompetent T lymphocytes start an autoimmune reaction against these newly differentiated myogenic cells. The clinical stage is reached when autosensitised effector T lymphocytes leave the thymus and either infiltrate the synaptic spaces of peripheral muscles or participate in the formation of autoantibodies, causing the neuromuscular symptoms. At two points the pathogenesis is under genetic control--the first at the differentiation of the stem-cells to myogenic cells and the second at the immune responsiveness of the lymphocytes to these atypical intrathymic muscle cells.

In vitro astrocytic differentiation from embryoid bodies of an experimental mouse testicular teratoma

Astrocytic differentiation in monolayer cultures of ascitic embryoid bodies from the experimental teratoma OTT-6050 was studied by conventional light microscopy and by indirect immunofluorescence with antisera to glial fibrillary acidic (GFA) protein, a protein specific for astorcytes. Primitive neuroepithelial cells were identified in 24-hour cultures. Within 72 hours, two cell types diverged. One cell type, with a flattened epithelial morphology in early cultures, demonstrated delicate GFA protein-positive fibrils within 48 hours. In later cultures, this type progressively displayed more typical stellate astrocytic features, with denser, more compact GFA protein-positive fluorescence in the perinuclear cytoplasm and cell processes. As indicated by GFA protein expression, the appearance of astrocytes of typical morphology therefore was preceded by biochemical differentiation. The second cell type, interpreted as neuroblastic, failed to demonstrate GFA protein and had a small perikaryon with slender bipolar processes that were argyrophilic with Bodian's protargol in late cultures. Divergent neuroepithelial differentiation occurred within mitotically active cell populations and proceeded without apparent tissue relationships to other germ layer derivatives.

Normal genetically mosaic mice produced from malignant teratocarcinoma cells

Malignant mouse teratocarcinoma (or embryonal carcinoma) cells with a normal modal chromosome number were taken from the "cores" of embryoid bodies grown only in vivo as an ascites tumor for 8 years, and were injected into blastocysts bearing many genetic markers, in order to test the developmental capacities, genetic constitution, and reversibility of malignancy of the core cells. Ninety-three live normal pre- and postnatal animals were obtained. Of 14 thus far analyzed, three were cellular genetic mosaics with substantial contributions of tumor-derived cells in many developmentally unrelated tissues, including some never seen in the solid tumors that form in transplant hosts. The tissues functioned normally and synthesized their specific products (e.g., immunoglobulins, adult hemoglobin, liver proteins) coded for by strain-type alleles at known loci. In addition, a tumor-contributed color gene, steel, not previously known to be present in the carcinoma cells, was detected from the coat phenotype. Cells derived from the carcinoma, which is of X/Y sex chromosome constitution, also contributed to the germ line and formed reproductively functional sperms, some of which transmitted the steel gene to the progeny. Thus, after almost 200 transplant generations as a highly malignant tumor, embryoid body core cells appear to be developmentally totipotent and able to express, in an orderly sequence in differentiation of somatic and germ-line tissues, many genes hitherto silent in the tumor of origin. This experimental system of "cycling" teratocarcinoma core cells through mice, in conjunction with experimental mutagenesis of those cells, may therefore provide a new and useful tool for biochemical, developmental, and genetic analyses of mammalian differentiation. The results also furnish an unequivocal example in animals of a non-mutational basis for transformation to malignancy and of reversal to normalcy. The origin of this tumor from a disorganized embryo suggests that malignancies of some other, more specialized, stem cells might arise comparably through tissue disorganization, leading to developmental aberrations of gene expression rather than changes in gene structure.

Differentiation of clonal lines of teratocarcinoma cells: formation of embryoid bodies in vitro

The differentiation in vitro of clonal pluripotent teratocarcinoma cells is reported. The first stage of this process is the formation of simple embryoid bodies which are identical to those found in animals bearing intraperitoneal teratocarcinomas. They consist of an inner core of embryonal carcinoma cells surrounded by a layer of endodermal cells which produce Reichert's membrane. The endodermal cells become apparent shortly after the embryonal carcinoma cells have formed aggregates which are loosely attached to the substratum. One clonal teratocarcinoma line was found to produce complex cystic embryoid bodies in vitro. Following formation of the endodermal cells, extensive differentiation to a wide variety of cell types occurs. There are similarities between the process of embryoid body formation and the early events of differentiation of the mouse embryo.