Interspecific hybrid cells

TABLE 2. Intraspecific and interspecific hybrid cells of agricultural animals, obtained in the laboratory of biotechnology (1982 2004)... 

Isolation and characterization of monosomal mouse cell lines and interspecific hybrid cells with single mouse chromosomes... 

Thus, judging from these three nonselective enzymes, examined in a number of rat X mouse and hamster X mouse somatic hybrids, it can be stated that both parental genomes are indeed functional in these cells. Moreover, it appears that in the quoted cases, the products of homologous genes, in spite of the evolutionary divergence of the latter, are similar enough to form fully functional hybrid molecules such hybrid molecules are probably very common in interspecific hybrid cells since many proteins are composed of subunits. 

We should now like to suggest a more complete interpretation covering the coordination, in interspecific hybrid cells, of the replication and expression of homologous genes of the two species directing the syntheses involved in cell doubling and preliminary to cell division. This interpretation will be based on the following assumptions ... 

Some wild species have larger capacities for osmotic adjustment, a trait which may improve yield during drought (Table 3, Turner, 1986). Interesting examples of this are Dubautia species from Hawaii which differ in osmotic adjustment mainly as a result of differences in cell wall elasticity. Interspecific hybrids can be made which have intermediate properties (Robichaux, Holsinger Morse, 1986). Material such as this could make a basis for the molecular study of differences in cell wall elasticity. 

Mutant cell cultures gave the possibility to obtain intraspecific and interspecific hybrid cultures of cells with lymphocytes, enterocytes and other not growing or badly growing in vitro cells (Table 2). 

GPRT- defective cells appear in population. Using the method of the selective pressure by 5-BDU and 8-Ag, the mutant cultures of cells, defective by the indicated enzymes, are obtained. The intraspecific and interspecific hybrid cultures of cells are firstly obtained in the laboratory of the cellular biotechnology, A4H (SPEV TK- x lymphocytes of horse) and others. Hybrid cultures possess the unique properties. They are the ability to grow in the monolayer and in suspension, the high sensitiveness to the viruses. Hybrid cultures PO-TK-KHLO, PO-TK-KHSO are sensible to the agent scrappy, what allows using them for the study of diseases, caused by prions. 

Pugliesi, C., Megale, P., Cecconi, F., and Baroncelli, S., Organogenesis and embryogenesis in Helianthus tubemsus and in interspecific hybrid Helianthus annuus x Helianthus tuberosus, Plant Cell Tiss. Organ Cult., 33, 187-193, 1993b. 

Witrzens, B., Scowcroft, W.R., Downes, R.W., and Larkin, P.J., Tissue culture and plant regeneration from sunflower (Helianthus annuus) and interspecific hybrids (H. tuberosus X H. armuus), Plant Cell Tiss. Organ Cult., 13, 61-76, 1988. 

Elicitation of active defense responses does not require an exogenous elicitor, since physical treatments such as UV irradiation and chilling can be very potent elicitors. Spontaneous active defense reactions also occur extensively in interspecific hybrids of Gossypium undergoing genetic lethal reactions (92). Thus, alterations in membranes or activation of chemical reactions in cell walls or on membranes may ultimately control active defense. 

Fukuhara, N. (1978) Meiotic observation in the pollen mother cell of interspecific hybrid between Chamaecyparis obtusa and C, pisifera. J. Jpn. For. Soc., 60 437-441. 

Before doing so, we wish to call attention to the fact that the karyotypic and phenotypic characteristics of the interspecific somatic hybrids will be presented in the order in which they were observed accordingly, we will give consideration first to rat X mouse and hamster X mouse hybrids. The implications of the properties of these hybrids will be discussed, and an attempt will be made to evaluate their significance in contributing to a general speculative picture of the coordination of replication processes in mammalian cells. We shall see later (Section IV, E) that, in the light of recent observations on some other interspecific hybrids, some of our conclusions may have to be amended. 

The viability of these hybrid cells permits an inference of interest from both the embryological and evolutionary points of view. The continuous multiplication and apparent permanence of hybrids between somatic cells of species phylogenetically as remote as the hamster, the rat, and the mouse, shows that, between somatic cells, there is no incompatibility similar to that observed in sexual interspecific crosses. It will be recalled that this incompatibility, in the extreme cases, results in the elimination of the foreign chromatin from the fertilized egg. It is clear therefore that the inviabiUty of sexual hybrids between remote forms, when they do contain both parental genomes, is due to their inadequacy for directing development and differentiation rather than to the inability of hybrid genotypes to control the balanced metabolism involved in cell replication. 

If these assumptions are accepted, the initial hypothesis may be restated more completely as follows In interspecific hybrids, the replication and configurational changes of all chromosomes, as well as the transcription of the homologous genes governing the different syntheses tvhich result in cell doubling, are timed with reference to a single fixed point of the new cell cycle. 

All the inferences and speculations presented thus far are based upon observations of the first-discovered interspecific hybrids— those between rat X mouse cells, and between mouse and (Chinese and Syrian) hamster cells. Some more recent observations made on three other hybrid combinations, appear as exceptions to the rule of coordination emphasized in the preceding Sections and may call for a modification of some of the hypotheses formulated above. We shall therefore describe now the peculiar features of these three new types of hybrids (recorded in Table 2) and then briefly consider their possible causes. 

The cause of protracted and possibly lethal asynchrony may reside in the formation of some hybrid molecules. The data presented in Section III, C suggest that, in interspecific hybrids, numerous (interspecific) hybrid molecules are formed. If it is assumed that the establishment of a coordinated hybrid cell cycle requires, at some point, the intervention of hybrid molecules, then the fusion product, which is really a mosaic, may not be synchronized until the molecules of parental types are diluted out by hybrid ones (hybrid membranes as well as hybrid enzymes may possibly be significant). 

The use of protoplasts in studies of stress physiology and biochemistry expands the advantages of cell culture systems discussed in the preceding sections. Additional applications are related to the fusion of protoplasts. Intraspecifie and interspecific protoplast fusion greatly enhance genetic variability of the fused protoplasts (Kumar Cocking, 1987). The resulting somatic hybrids provide cells which can be used for selection of specific traits (e.g. environmental stress tolerance) provided by one or both donor cells and for basic studies on cytoplasmic and nuclear inheritance of desired characteristics. 

Hybrid cultures as well as other permanent lines of cells maintain the deep freezing (-196 C) and are saved this way. One of the problems of hybrid cultures maintenance and cultivation, especially interspecific, is the segregation of chromosomes. Therefore, the control of desirable correlation saving between hybridization partners chromosomes is obligatory. 

Interspecific cell hybrids between human and murine cells do not express the rDNA genes of both genes. Interspecific crosses in plants and between Xenopus species have also shown a gene-specific dominance effect. This phenomenon is known as nucleolar dominance and, depending on the chromosomal organization of the hybrid, the rDNA of either one of the species is expressed (Reeder, 1985). These findings indicated that there are some aspects of rDNA transcription that are species specific. The incompatibility between different species has then been... 

Regulation of the Cell Cycle in Mammalian Cells Inferences and Speculations Based on Observations of Interspecific Somatic Hybrids... 

Intercellular control of the functions of mammalian cells has been long since evidenced by observations of experimental embryologists and, in recent years, one form of it, contact inhibition, discovered by Abercrombie and Heayesman (1954), has been a most popular subject of study. Contact inhibition is certainly one type of control which is generally not found in bacteria and this difference must be directly correlated with differences between the structures of bacterial and mammalian cell surfaces. Other differences between the structures of bacterial and mammalian cells are the presence in the latter of a nuclear membrane and of an elaborate mitotic apparatus. We shall have little to say about the latter and shall consider mainly the nuclear membrane, to which, we think, are delegated certain functions assumed, in bacteria, by the cell membrane and concerned with die coordinated replication of the chromosomes (Jacob et al., 1963). This idea represents one of a number of inferences from recent observations made in our laboratories on interspecific somatic hybrids between mammalian cells, and it is the primary purpose of this paper to present the evidence on which it is based (Note 2). 

Returning to our speculations on the coordination of biochemical events in mononucleate interspecific somatic hybrids, we would like to go one step further and suggest that the synchronization of the two parental cell cycles to produce a single new cycle is in part the consequence of the attachment of (some or all ) chromosomes of both species to the single nuclear membrane and hence of their simultaneous response to the reaction of the nuclear membrane to the signal initiating DNA synthesis. 

Owing to the apparently frequent differences in physical properties of enzymes of remote mammalian species, similar experiments should be possible with interspecific somatic hybrids and should thus provide evidence on the vahdity of these speculations. In principle (and we emphasize in principle ), the approximate alignment due to linear transcription should result in more or less clearly spaced bursts of homologous enzymes in the cell cycle of synchronized populations. Coordination by an induction-repression mechanism should, on the contrary, result in the simultaneous synthesis of homologous enzymes. 

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