Solid tissues can be manipulated ex vivo and used as vehicles for gene therapy.

BACKGROUND: Organ fragments can be cultured for weeks in vitro if they are prepared of microscopic thickness and if the basic organ structure is preserved. Such organ fragments, which we termed micro-organs (MOs), express in culture endogenous tissue-specific gene products. We have exploited this methodology to engineer MOs ex vivo by gene transfer. METHODS: MOs prepared from spleen, lung, colon and skin were infected using: herpes simplex type-1, adeno virus, vaccinia virus and murine leukemia virus (MuLV), carrying the reporter gene beta-galactosidase. RESULTS: All four viral vectors infected MOs in culture, with adeno infection giving significantly higher values. After optimization, high levels of expression (> 15% positive cells), comparable to those obtained with the adeno construct, were also obtained using the MuLV construct both in vitro and after implantation into syngeneic hosts. After implantation, the engineered tissue was found to remain localized, become vascularized, and to express the transduced gene for several months. CONCLUSIONS: The system can be used to study interactions between viruses and tissues both ex vivo and in vivo. Furthermore, the approach proposes a novel platform for ex vivo gene therapy. Such engineered structures could be used as autologous biological pumps for continuous secretion in vivo of gene products of clinical importance.

Expression pattern and secretion of human and chicken heparanase are determined by their signal peptide sequence.

Cleavage of heparan sulfate (HS) proteoglycans affects the integrity and function of tissues and thereby fundamental phenomena, involving cell migration and response to changes in the extracellular microenvironment. The role of HS-degrading enzymes, commonly referred to as heparanases, in normal development has not been identified. The present study focuses on cloning, expression, and properties of a chicken heparanase and its distribution in the developing chicken embryo. We have identified a chicken EST, homologous to the recently cloned human heparanase, to clone and express a functional chicken heparanase, 60% homologous to the human enzyme. The full-length chicken heparanase cDNA encodes a 60-kDa proenzyme that is processed at the N terminus into a 45-kDa highly active enzyme. The most prominent difference between the chicken and human enzymes resides in the predicted signal peptide sequence, apparently accounting for the chicken heparanase being readily secreted and localized in close proximity to the cell surface. In contrast, the human enzyme is mostly intracellular, localized in perinuclear granules. Cells transfected with a chimeric construct composed of the chicken signal peptide preceding the human heparanase exhibited cell surface localization and secretion of heparanase, similar to cells transfected with the full-length chicken enzyme. We examined the distribution pattern of the heparanase enzyme in the developing chicken embryo. Both the chicken heparanase mRNA and protein were expressed, as early as 12 h post fertilization, in cells migrating from the epiblast and forming the hypoblast layer. Later on (72 h), the enzyme is preferentially expressed in cells of the developing vascular and nervous systems. Cloning and characterization of heparanase, the first and single functional vertebrate HS-degrading enzyme, may lead to identification of other glycosaminoglycan degrading enzymes, toward elucidation of their significance in normal and pathological processes.

Validity study of the EDI-2 in Israeli population.

This study was designed to validate the EDI-2 (1) in an Israeli population. The sample consisted of 29 anorectic patients and 18 recovering anorectics, recruited from six hospitals, and 67 female control subjects matched by age. Results of the validity study indicate that the translated EDI-2 was reliable and valid. Anorectic patients scored higher than the recovering anorectics on most scales. Recovering anorectics resembled the control subjects on most scales except Perfectionism.

Activin can generate ectopic axial structures in chick blastoderm explants.

We have recently shown that activin can induce the formation of axial structures from chick blastulae and that activin beta-B is transcribed, in the hypoblast of the chick, at the same stage that axial mesoderm is being induced. It was not clear, however, whether activin was merely allowing the central epiblastic cells to express a differentiated phenotype for which they were already prepared. This report shows that activin-containing medium (ACM) can act as an instructive inductor, which can change the fate of competent cells and bring about the formation of an ectopic embryonic axis. Furthermore, we show data that suggest that during normal development only one axis is obtained as a result of a carefully controlled inhibitory process.

Activin can induce the formation of axial structures and is expressed in the hypoblast of the chick.

We show that PIF/activin can induce the formation of axial structures including a full-length notochord, segmented somites, and a neural tube in isolated epiblasts from chick blastulae. Using degenerate PCR primers, we have cloned a fragment of the activin beta B chain from chick hypoblast cDNA, and a fragment of the activin beta A chain from chick genomic DNA. Furthermore, we show that in the chick, activin is transcribed precisely when axial mesoderm is being induced. Since exogenous PIF/activin can induce the formation of axial structures and since activin beta B is transcribed at the time and place where the mesodermal axial structures are being induced, we propose that in the chick, activin B is the endogenous inducer of the body axis.

Fibroblast growth factor during mesoderm induction in the early chick embryo.

A chick genomic clone that reveals a high degree of homology to the mammalian and Xenopus bFGF gene has been isolated. The pattern of expression of bFGF has been examined during early chick embryogenesis. RNA blot analysis revealed that chick bFGF is already transcribed at pregastrula stages. Immunolabeling analysis indicated that bFGF protein is present at these early developmental stages and is distributed evenly in the epiblast, hypoblast and marginal zone of the chick blastula. Substances that can inhibit FGF action were applied to early chick blastoderms grown in vitro under defined culture conditions (DCM). Both heparin and suramin were capable of blocking the formation of mesodermal structures in a dose-dependent manner. Our results indicate that FGF-like substances may need to be present for axial structures to develop although they may be acting earlier during the induction of non-axial mesoderm.

Induction by soluble factors of organized axial structures in chick epiblasts.

Inductive action of soluble factors was tested on isolated chick epiblasts. An assay was developed wherein conditioned medium derived from the Xenopus XTC cell line induced the formation of a full-length notochord and rows of bilaterally symmetric somites. Basic fibroblast growth factor, epidermal growth factor, retinoic acid, and transforming growth factor type B1 and B2 were not capable of inducing axial structures. Thus, soluble factors can elicit the development of polarity stored in the epiblast and behave as true morphogens since they can induce the formation of the organized complex structures that constitute the embryonic axis.

Retinoic acid inhibits growth in agarose of early chick embryonic cells and may be involved in regulation of axis formation.

The mechanisms involved in the generation of axial structures in the chick are well documented, yet, little is known about the actual factors that generate such a complex pattern. The recent demonstrations that all-trans-retinoic acid (RA) acts as a morphogen during limb development (Thaller and Eichele, 1987) lead us to examine whether during axis formation in the developing chick, RA could be one of the factors involved. We now show that retinoic acid can block a very unusual property of normal early chick embryonic cells, mainly their capacity to grow in semisolid medium. We also present experiments that suggest that RA may play a direct role during axis formation in the developing chick.

Rous sarcoma virus is integrated but not expressed in chicken early embryonic cells.

We have developed a protocol that allows us to infect chicken early embryonic (CEE) cells with high efficiency. This was achieved by exposing the CEE cells to a semicontinuous dose of Rous sarcoma virus (RSV) for a period of 20 hr. Southern blot analysis indicated that an average of one proviral copy is integrated per embryonic cell. However, there was no production of infectious viral particles by the cells containing the proviral genome, although low levels of full-length genomic RNA could be detected by RNA transfer blot analysis. These low RNA levels contrast with the 100- to 1000-fold higher levels found in RSV-infected chicken embryo fibroblasts. We conclude that in cells derived from pregastrulating chicken embryos, RSV DNA is integrated into the cell genome but fails to be expressed in an efficient manner. These primary cells can therefore be used to identify factors involved in regulation of retroviral gene expression in normal cells. Such factors may also be instrumental in elucidating basic mechanisms involved in gene regulation during early development in higher vertebrates.

Restriction of cloning potential in agarose of early chick embryonic cells as development progresses.

Early chick embryonic cells, prior to the formation of the primitive streak, form colonies when cultured in soft agarose [Mitrani, E.: Exp. Cell Res. 152, 148-153 (1984)]. The present work is an attempt to determine at which stages of development this ability is expressed and which areas of the chick embryo harbour the colony-forming cells. We found that the capacity to form colonies decreases as development progresses and cells enter alternative differentiation pathways. At pre-primitive streak stages, the capacity is concentrated to the peripheral areas of the embryo and decreases towards the centre. With the onset of hypoblast formation only cells from Area Opaca and, to a lesser degree, the Marginal Zone, can form colonies in agarose. At post-primitive streak stages only extra-embryonic cells can form colonies in agarose. By 48 h of incubation all cells of the chick blastoderm seem to have lost the capacity to form colonies in agarose.

Developmental potencies of area opaca and marginal zone areas of early chick blastoderms.

The marginal zone, in pregastrulating chick blastoderms, has been defined as the intermediate ring between the epiblast proper and the most external region, the area opaca (Spratt & Haas, 1960). Azar & Eyal-Giladi (1979) have shown that the marginal zone of a stage XIII blastoderm has the capacity of regenerating an inductive layer which when in contact with a competent stage XIII epiblast can cause the formation of axial structures. The present work demonstrates that at stage X (Eyal-Giladi & Kochav, 1976) the marginal zone can both induce and respond to its own inductive stimulus by forming an embryonic axis. By stage XIII the marginal zone seems to have lost its competence to respond to an inductive stimulus and cannot form an embryonic axis. It is further shown that at stages X--XIII the area opaca is neither competent to develop any sort of axial structures nor has the capacity to generate an inductive layer.

Early chick embryonic cells can form clones in agarose cultures.

Early chick embryonic cells prior to the formation of the primitive streak, have been cultured in a two-layer soft-agarose system. Single, primary cells when grown in this system were capable of producing colonies ranging in size from 30 to 100 cells. The plating efficiency varied between 1 and 5% and the colonies remained viable for about 2 weeks. We believe this is the first report of normal, non-passaged cells which show anchorage-independent growth properties by forming colonies in a standard agarose culture in the absence of additional factors. The importance of being able to use normal monoclonal embryonic cell populations in studying early developmental processes is also discussed.

Is upward basal cell movement independent of mitosis in the normal epidermis?

An analysis has been made of the possible mechanisms by which cells leave the basal layer distally during cell replacement in the steady state mammalian epidermis. Etoh's concept (1975) of cells actively migrating from the basal layer is challenged. Computer experiments suggest that if basal cell migration is an active process, the rate of cell migration consistent with the kinetics of the process being examined would yield a depopulation value far higher than the one observed experimentally. We found by contrast that rates of migration comparable to those found experimentally after mitosis inhibition by irradiation were obtained in our computer simulation experiments if it was assumed that distal basal cell migration is a passive event resulting from cells being extruded from the basal layer. We believe that there is not at present sufficient data to support the concept of active cell migration from the basal layer. The evidence favours the concept that in normal steady state epidermal populations, cells are passively removed from the basal layer as a result of forces generated, directly or indirectly, by dividing cells.

Nature of the hypoblastic influence on the chick embryo epiblast.

Stage XIII chick blastoderms deprived of the marginal zone, the area opaca and the posterior half of the hypoblast, when incubated further developed axes whose orientation in 50% of the cases was according to the original blastoderm's orientation, whilst in 50% of the cases they developed at 90 degrees from the posterior side. Those results illustrate the quantitative differences in inductivity between the anterior and the posterior hypoblastic halves. Normally the posterior region has the highest effect but other regions can also bring about the development of an embryonic axis if allowed to act upon the epiblast for a sufficiently long period of time. The possible ways in which a chick hypoblast influences the epiblast to develop an embryo are examined in the light of recent findings and of new experiments described below.

A general method for evaluating the cell cycle time in mammalian epidermis.

A method is proposed for the evaluation of the cell cycle time of in vivo steady state populations. It requires only an accurate estimation of either the labelling index or the mitotic index and an approximate evaluation of the period between the initiation of the S phase and the completion of mitosis. The method proposed takes into account the fact that the cell cycle is non-deterministic, the angle at which cells divide and the effect of cell extrusion from the basal layer, plus the fact that the cells can only be extruded when in certain phases of the cell cycle. Limitations of other methods recently reported are discussed.

Procollagen localisation in normal, premalignant and malignant lesions of the epidermis.

The distribution of procollagen in normal hyperplastic, preneoplastic or neoplastic human epidermal lesions has been analysed in indirect immunofluorescence tests with the antibodies to procollagen raised in sheep to extracted procollagen, synthesised by newborn rat skin explants in culture. These antiprocollagen antibodies produced indirect immunofluorescence staining only of the papillary dermis of human skin. We reacted serial dilutions of the antibody with each skin lesion and recorded the maximum dilution at which a positive reaction was observed. All lesions examined displayed essentially the same procollagen immunofluorescence pattern. The fluorescence was localised as a fibrillar/diffuse area just under the epidermis. In conditions in which the epidermis is highly convoluted, the fluorescent band was found to follow the pattern of the epidermis and to surround epidermal 'islands' in the deeper dermis. Our observations suggest that in the neoplastic lesions a new dermal topography, resembling the stratum papillare of normal human skin, is found in the deeper dermis surrounding the epidermal islands produced as the epidermal mass increases and invaginates further into the stroma. Malignant epidermal lesions were found to show a positive procollagen immunofluorescent staining at tenfold lower concentrations of the antibody than normal human skin in subepidermal regions.

Hypoblastic cells can form a disk inducing an embryonic axis in chick epiblast.

The primitive streak of the chick embryo develops from one of the two layers of cells of the stage XIII blastoderm, the epiblast. The other layer of cells, the hypoblast, seems to be necessary for the induction of the primitive streak and also determines its orientation--rotation of the hypoblast by 90 degrees is followed by a similar rotation of the embryonic axis. After stage XIII, the hypoblast is replaced by the invaginating endoderm and plays no further part in the development of the embryo. By means of a technique for disaggregation and reconstituting cells of stage XIII hypoblasts, we have been able to show that the two functions, induction and orientation are independent and that with reconstituted hypoblasts, the orientation of the primitive streak is determined by the epiblast.