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Terminology Associated with Cell, Tissue and Organ Culture, Molecular Biology and Molecular Genetics

When areas of research become interdisciplinary their jargon, techniques and bodies of information are utilized widely in diverse disciplines. At such times, reciprocal use of terminology by individuals who had not previously used it is often misused and, therefore, confusion occurs. This confusion is especially acute in the field of vertebrate, invertebrate and plant cell culture. There is hardly a field of biological investigation in which culturing of such cells is not employed. Similarly, molecular biology and molecular genetics are lending their technology to an ever widening group of researchers who are communicating in a more global sense via scientific presentations, publications and research proposals. Unfortunately often the writer and reader represent different areas of specialization who have been brought together by the common technology used in their work. As such, misuse of terminology can prove unfortunate indeed; anything from inability to repeat a piece of research to problems in publishing a paper or obtaining funding of a research proposal. The following glossary, approved by the Society for In Vitro Biology, Terminology Committee is published in an effort to increase communication between scientists and between scientists and the lay community.

Adventitious: Developing from unusual points of origin, such as shoots or root tissues from callus or embryos from sources other than zygotes. This term can also be used to describe agents which contaminate cell cultures.

Anchorage-dependent cells or cultures: Cells, or cultures derived from them, which will grow, survive, or maintain function only when attached to a surface such as glass or plastic. The use of this term does not imply that the cells are normal or that they are or are not neoplastically transformed.

Aneuploid: The situation which exists when the nucleus of a cell does not contain an exact multiple of the haploid number of chromosomes; one or more chromosomes being present in greater or lesser number than the rest. The chromosomes may or may not show rearrangements.

Asepsis: Without infection or contaminating microorganisms.

Aseptic technique: Procedures used to prevent the introduction of fungi, bacteria, viruses, mycoplasma or other microorganisms into cell, tissue and organ cultures. Although these procedures are used to prevent microbial contamination of cultures, they also prevent cross contamination of cell cultures as well. These procedures may or may not exclude the introduction of infectious molecules.

Attachment efficiency: The percentage of cells plated (seeded, inoculated) which attach to the surface of the culture vessel within a specified period of time. The conditions under which such a determination is made should always be stated.

Autocrine cell: In animals, a cell which produces hormones, growth factors or other signalling substances for which it also expresses the corresponding receptors. (See also endocrine and paracrine)

Axenic culture: A culture without foreign or undesired life forms. An axenic culture may include the purposeful cocultivation of different types of cells, tissues or organisms.

Callus: An unorganized, proliferative mass of differentiated plant cells; a wound response.

Cell culture: Term used to denote the maintenance or cultivation of cells in vitro including the culture of single cells. In cell cultures, the cells are no longer organized into tissues.

Cell generation time: The interval between consecutive divisions of a cell. This interval can best be determined, at present, with the aid of cinephotomicrography. This term is not synonymous with "population doubling time ".

Cell hybridization: The fusion of two or more dissimilar cells leading to the formation of a synkaryon.

Cell line: A cell line arises from a primary culture at the time of the first successful subculture. The term cell line implies that cultures from it consist of lineages of cells originally present in the primary culture. The terms finite or continuous are used as prefixes if the status of the culture is known. If not, the term line will suffice. The term "continuous line" replaces the term "established line". In any published description of a culture, one must make every attempt to publish the characterization or history of the culture. If such has already been published, a reference to the original publication must be made. In obtaining a culture from another laboratory, the proper designation of the culture, as originally named and described, must be maintained and any deviations in cultivation from the original must be reported in any publication.

Cell strain: A cell strain is derived either from a primary culture or a cell line by the selection or cloning of cells having specific properties or markers. In describing a cell strain, its specific features must be defined. The terms finite or continuous are to be used as prefixes if the status of the culture is known. If not, the term strain will suffice. In any published description of a cell strain, one must make every attempt to publish the characterization or history of the strain. If such has already been published, a reference to the original publication must be made. In obtaining a culture from another laboratory, the proper designation of the culture, as originally named and described, must be maintained and any deviations in cultivation from the original must be reported in any publication.

Chemically defined medium: A nutritive solution for culturing cells in which each component is specifiable and, ideally, is of known chemical structure.

Clonal propagation: Asexual reproduction of plants that are considered to be genetically uniform and originated from a single individual or explant.

Clone: In animal cell culture terminology a population of cells derived from a single cell by mitoses. A clone is not necessarily homogeneous and, therefore, the terms clone and cloned do not indicate homogeneity in a cell population, genetic or otherwise. In plant culture terminology, the term may refer to a culture derived as above or it may refer to a group of plants propagated only by vegetative and asexual means, all members of which have been derived by repeated propagation from a single individual.

Cloning efficiency: The percentage of cells plated (seeded, inoculated) that form a clone. One must be certain that the colonies formed arose from single cells in order to properly use this term. (See "Colony forming efficiency")

Colony forming efficiency: The percentage of cells plated (seeded, inoculated) that form a colony.

Complementation: The ability of two different genetic defects to compensate for one another.

Contact inhibition of locomotion: A phenomenon characterizing certain cells in which two cells meet, locomotory activity diminishes and the forward motion of one cell over the surface of the other is stopped.

Continuous cell culture: A culture which is apparently capable of an unlimited number of population doublings; often referred to as an immortal cell culture. Such cells may or may not express the characteristics of in vitro neoplastic or malignant transformation. (See also "immortalization")

Crisis: A stage of the in vitro transformation of cells. It is characterized by reduced proliferation of the culture, abnormal mitotic figures, detachment of cells from the culture substrate, and the formation of multinucleated or giant cells. During this massive cultural degeneration, a small number of colonies usually, but not always, survive and give rise to a culture with an apparent unlimited in vitro lifespan. This process was first described in human cells following infection with an oncogenic virus (SV40). See also "cell line", "in vitro transformation" and "in vitro senescence".

Cryopreservation: Ultra-low temperature storage of cells, tissues, embryos or seeds. This storage is usually carried out using temperatures below 100° C

Cumulative population doublings: See "population doubling level".

Cybrid: The viable cell resulting from the fusion of a cytoplast with a whole cell, thus creating a cytoplasmic hybrid.

Cytoplast: The intact cytoplasm remaining following the enucleation of a cell.

Cytoplasmic hybrid: Synonymous with "cybrid".

Cytoplasmic inheritance: Inheritance attributable to extranuclear genes; for example genes in cytoplasmic organelles such as mitochondria or chloroplasts, or in plasmids, etc.

Density dependent inhibition of growth: Mitotic inhibition correlated with increased cell density.

Differentiated: Cells that maintain, in culture, all or much of the specialized structure and function typical of the cell type in vivo.

Diploid: The state of the cell in which all chromosomes, except sex chromosomes, are two in number and are structurally identical with those of the species from which the culture was derived. Where there is a Commission Report available, the experimenter should adhere to the convention for reporting the karyotype of the donor. Commission Reports have been published for mouse (1), human (2) and rat (3). In defining a diploid culture, one should present a graph depicting the chromosome number distribution leading to the modal number determination along with representative karyotypes.

Electroporation: Creation, by means of an electrical current, of transient pores in the plasmalemma usually for the purpose of introducing exogenous material, especially DNA, from the medium.

Embryo culture: In vitro development or maintenance of isolated mature or immature embryos.

Embryogenesis: The process of embryo initiation and development.

Endocrine cell: In animals, a cell which produces hormones, growth factors or other signalling substances for which the target cells, expressing the corresponding receptors, are located at a distance. (See also autocrine and paracrine)

Epigenetic event: Any change in a phenotype which does not result from an alteration in DNA sequence. This change may be stable and heritable and includes alteration in DNA methylation, transcriptional activation, translational control and posttranslational modifications.

Epigenetic variation: Phenotypic variability which has a nongenetic basis.

Epithelial-like: Resembling or characteristic of, having the form or appearance of epithelial cells. In order to define a cell as an epithelial cell, it must possess characteristics typical of epithelial cells. Often one can be certain of the histologic origin and/or function of the cells placed into culture and, under these conditions, one can be reasonably confident in designating the cells as epithelial. It is incumbent upon the individual reporting on such cells to use as many parameters as possible in assigning this term to a culture. Until such time as a rigorous definition is possible, it would be most correct to use the term epithelial-like.

Euploid: The situation which exists when the nucleus of a cell contains exact multiples of the haploid number of chromosomes.

Explant: Tissue taken from its original site and transferred to an artificial medium for growth or maintenance.

Explant culture: The maintenance or growth of an explant in culture.

Feeder layer: A layer of cells (usually lethally irradiated for animal cell culture) upon which are cultured a fastidious cell type. (See also "nurse culture"}

Fibroblast-like: Resembling or characteristic of, having the form or appearance of fibroblast cells. In order to define a cell as a fibroblast cell, it must possess characteristics typical of fibroblast cells. Often one can be certain of the histologic origin and/or function of the cells placed into culture and under these conditions, one can be reasonably confident in designating the cells as fibroblast. It is incumbent upon the individual reporting on such cells to use as many parameters as possible in assigning this term to a culture. Until such time as a rigorous definition is possible, it would be most correct to use the term fibroblast-like.

Finite cell culture: A culture which is capable of only a limited number of population doublings after which the culture ceases proliferation. (See in vitro senescence)

Friability: A term indicating the tendency for plant cells to separate from one another.

Gametoclonal variation: Variation in phenotype, either genetic or epigenetic in origin, expressed by gametoclones.

Gametoclone: Plants regenerated from cell cultures derived from meiospores, gametes or gametophytes.

Habituation: The acquired ability of a population of cells to grow and divide independently of exogenously supplied growth regulators.

Heterokaryon: A cell possessing two or more genetically different nuclei m a common cytoplasm, usually derived as a result of cell-to-cell fusion.

Heteroploid: The term given to a cell culture when the cells comprising the culture possess nuclei containing chromosome numbers other than the diploid number. This is a term used only to describe a culture and is not used to describe individual cells. Thus, a heteroploid culture would be one which contains aneuploid cells.

Histiotypic: The in vitro resemblance, of cells in culture, to a tissue in form or function or both. For example, a suspension of fibroblast-like cells may secrete a glycosaminoglycancollagen matrix and the result is a structure resembling fibrous connective tissue, which is, therefore, histiotypic. This term is not meant to be used along with the word "culture". Thus, a tissue culture system demonstrating form and function typical of cells in vivo would be said to be histiotypic.

Homokaryon: A cell possessing two or more genetically identical nuclei in a common cytoplasm, derived as a result of cell-to-cell fusion.

Hybrid cell: The term used to describe the mononucleate cell which results from the fusion of two different cells, leading to the formation of a synkaryon.

Hybridoma: The cell which results from the fusion of an antibody producing tumor cell (myeloma) and an antigenically-stimulated normal plasma cell. Such cells are constructed because they produce a single antibody directed against the antigen epitope which stimulated the plasma cell. This antibody is referred to as a monoclonal antibody.

Immortalization: The attainment by a finite cell culture, whether by perturbation or intrinsically, of the attributes of a continuous cell line. An immortalized cell is not necessarily one which is neoplastically or malignantly transformed.

Immortal cell culture: See continuous cell culture.

Induction: Initiation of a structure, organ or process in vitro.

In vitro neoplastic transformation: The acquisition, by cultured cells, of the property to form neoplasms, benign or malignant, when inoculated into animals. Many transformed cell populations which arise in vitro intrinsically or through deliberate manipulation by the investigator, produce only benign tumors which show no local invasion or metastasis following animal inoculation. If there is supporting evidence, the term "in vitro malignant neoplastic transformation" or "in vitro malignant transformation" can be used to indicate that an injected cell line does, indeed, invade or metastasize.

In vitro propagation: Propagation of plants in a controlled, artificial environment, using plastic or glass culture vessels, aseptic techniques and a defined growing medium.

In vitro senescence: In vertebrate cell cultures, the property attributable to finite cell cultures; namely, their inability to grow beyond a finite number of population doublings. Neither invertebrate nor plant cell cultures exhibit this property.

In vitro transformation: A heritable change, occurring in cells in culture, either intrinsically or from treatment with chemical carcinogens, oncogenic viruses, irradiation, transfection with oncogenes, etc. and leading to the acquisition of altered morphological, antigenic, neoplastic, proliferative or other properties. This expression is distinguished from "in vitro neoplastic transformation" in that the alterations occurring m the cell population may not always include the ability of the cells to produce tumors in appropriate hosts. The type of transformation should always be specified in any description.

Juvenile: A phase in the sexual cycle of a plant characterized by differences in appearance from the adult and which lacks the ability to respond to flower-inducing stimuli.

Karyoplast: A cell nucleus, obtained from the cell by enucleation, surrounded by a narrow rim of cytoplasm and a plasma membrane.

Line: See cell line.

Liposome: A closed lipid vesicle surrounding an aqueous interior; may be used to encapsulate exogenous materials for ultimate delivery of these into cells by fusion with the cell.

Meristem culture: In vitro culture of a generally shiny, dome-like structure measuring less than 0.1 mm in length when excised, most often excised from the shoot apex.

Microcell: A cell fragment, containing one to a few chromosomes, which is formed by the enucleation or disruption of a micronucleated cell.

Micronucleated cell: A cell which has been mitotically arrested and in which small groups of chromosomes function as foci for the reassembly of the nuclear membrane thus forming micronuclei the maximum of which could be equal to the total number of chromosomes.

Micropropagation: In vitro clonal propagation of plants from shoot tips or nodal explants, usually with an accelerated proliferation of shoots during subcultures.

Morphogenesis: (a) The evolution of a structure from an undifferentiated to a differentiated state. (b) The process of growth and development of differentiated structures.

Mutant: A phenotypic variant resulting from a changed or new gene.

Nurse culture: In the culture of plant cells, the growth of a cell or cells on a contiguous culture of different origin which in turn is in contact with the tissue culture medium. The cultured cell or tissue may be separated from the feeder layer by a porous matrix such as filter paper or membranous filters. (See also "feeder layer")

Organ culture: The maintenance or growth of organ primordia or the whole or parts of an organ in vitro in a way that may allow differentiation and preservation of the architecture and/or function.

Organized: Arranged into definite structures.

Organogenesis: The evolution, from dissociated cells, of a structure which shows natural organ form or function or both.

Organotypic: Resembling an organ in vivo in three dimensional form or function or both. For example, a rudimentary organ in culture may differentiate in an organotypic manner, or a population of dispersed cells may become rearranged into an organotypic structure and may also function in an organotypic manner. This term is not meant to be used along with the word "culture" but is meant to be used as a descriptive term.

Paracrine: In animals, a cell which produces hormones, growth factors or other signalling substances for which the target cells, expressing the corresponding receptors, are located in its vicinity, or in a group adjacent to it. (See also autocrine and endocrine)

Passage: The transfer or transplantation of cells, with or without dilution, from one culture vessel to another. It is understood that any time cells are transferred from one vessel to another, a certain portion of the cells may be lost and, therefore, dilution of cells, whether deliberate or not, may occur. This term is synonymous with the term "subculture".

Passage number: The number of times the cells m the culture have been subcultured or passaged. In descriptions of this process, the ratio or dilution of the cells should be stated so that the relative cultural age can be ascertained.

Pathogen free: Free from specific organisms based on specific tests for the designated organisms.

Plant tissue culture: The growth or maintenance of plant cells, tissues, organs or whole plants in vitro.

Plating efficiency: This is a term which originally encompassed the terms, "Attachment ("Seeding") efficiency", "Cloning efficiency", and "Colony forming efficiency" and which is now better described by using one or more of them in its place as the term "plating" is not sufficiently descriptive of what is taking place. (See "Attachment, Seeding, Cloning, Colony forming efficiency")

Population density: The number of cells per unit area or volume of a culture vessel. Also the number of cells per unit volume of medium in a suspension culture.

Population doubling level: The total number of population doublings of a cell line or strain since its initiation in vitro. A formula to use for the calculation of "population doublings" in a single passage is: number of population doublings = Log (N/No ) X 3.33 where: N=number of cells in the growth vessel at the end of a period of growth. No=number of cells plated in the growth vessel. It is best to use the number of viable cells or number of attached cells for this determination. Population doubling level is synonymous with "cumulative population doublings".

Population doubling time: The interval, calculated during the logarithmic phase of growth in which, for example, 1.0 X 106 cells increase to 2.0 X 106 cells. This term is not synonymous with "cell generation time".

Primary culture: A culture started from cells, tissues or organs taken directly from organisms. A primary culture may be regarded as such until it is successfully subcultured for the first time. It then becomes a "cell line".

Protoplast: A cell from which the entire cell wall has been removed. This term is used to describe such plant, bacterial or fungal cells. (See spheroplast for comparison. )

Protoplast fusion: Technique in which protoplasts are fused into a single cell.

Pseudodiploid: This describes the condition where the number of chromosomes in a cell is diploid but, as a result of chromosomal rearrangements, the karyotype is abnormal and linkage relationships may be disrupted.

Recon: The viable cell reconstructed by the fusion of a karyoplast with a cytoplast.

Reconstituted cell: Synonymous with "Recon".

Reconstructed cell: Synonymous with "Recon".

Reculture: The process by which a cell monolayer or a plant explant is transferred, without subdivision, into fresh medium. (See also "Passage")

Regeneration: In plant cultures, a morphogenetic response to a stimulus that results in the production of organs, embryos or whole plants.

Saturation density: The maximum cell number attainable, under specified culture conditions, in a culture vessel. This term is usually expressed as the number of cells per square centimeter in a monolayer culture or the number of cell per cubic centimeter in a suspension culture.

Seeding efficiency: (See "Attachment efficiency")

Senescence: (See "In vitro senescence")

Shoot apical meristem: Undifferentiated tissue, located within the shoot tip, generally appearing as a shiny dome-like structure distal to the youngest leaf primordium and measuring less than 0.1 mm in length when excised.

Shoot tip (apex) culture: A structure consisting of the shoot apical meristem plus one to several primordial leaves, usually measuring from 0.1-1.0 mm in length; in instances where more mature leaves are included, the structure can measure up to several centimeters in length.

Somaclonal variation: Phenotypic variation, either genetic or epigenetic in origin, displayed among somaclones.

Somaclone: Plants derived from any form of cell culture involving the use of somatic plant cells.

Somatic cell hybrid: The cell or plant resulting from the fusion of animal cells or plant protoplasts respectively, derived from somatic cells which differ genetically.

Somatic cell genetics: The study of genetic phenomena of somatic cells. The cells under study are most often cells grown in culture.

Somatic cell hybridization: The in vitro fusion of animal cells or plant protoplasts derived from somatic cells which differ genetically.

Somatic embryogenesis: In plant culture, the process of embryo initiation and development from vegetative or nongametic cells.

Spheroplast: A cell from which most of the cell wall has been removed. (See "protoplast" for comparison.)

Stage I: A step in in vitro propagation characterized by the establishment of an aseptic tissue culture of a plant.

Stage II: A step in in vitro plant propagation characterized by the rapid numerical increase of organs or other structures.

Stage III: A step in in vitro plant propagation characterized by preparation of propagules for successful transfer to soil, a process involving rooting of shoot cuttings, hardening of plants and initiating the change from the heterotrophic to the autotrophic state.

Stage IV: A step in in vitro plant propagation characterized by the establishment in soil of a tissue culture derived plant, either after undergoing a Stage III pretransplant treatment or, in certain species, after the direct transfer of plants from Stage II into soil.

Sterile: (a) Without Life. (b) Inability of an organism to produce functional gametes.

Strain: See "cell strain".

Subculture: See "passage". With plant cultures, this is the process by which the tissue or explant is first subdivided, then transferred into fresh culture medium.

Substrain: A substrain can be derived from a strain by isolating a single cell or groups of cells having properties or markers not shared by all cells of the parent strain.

Surface or substrate dependent cells or cultures: See "anchorage dependent cells".

Suspension culture: A type of culture in which cells, or aggregates of cells, multiply while suspended in liquid medium.

Synkaryon: A hybrid cell which results from the fusion of the nuclei it carries.

Tissue culture: The maintenance or growth of tissues, in vitro, in a way that may allow differentiation and preservation of their architecture and/or function.

Totipotency: A cell characteristic in which the potential for forming all the cell types in the adult organism is retained.

Transfection: The transfer, for the purposes of genomic integration, of naked, foreign DNA into cells in culture. The traditional microbiological usage of this term implied that the DNA being transferred was derived from a virus. The definition as stated here is that which is in use to describe the general transfer of DNA irrespective of its source. (See also "transformation".)

Transformation: In plant cell culture, the introduction and stable genomic integration of foreign DNA into a plant cell by any means, resulting in a genetic modification. This definition is the traditional microbiological definition. For animal cell culture, see "in vitro transformation", "in vitro neoplastic transformation" and "transfection".

Type I callus: A type of adventive embryogenesis found with gramineous monocots, which has been induced on an explant where the somatic embryos are arrested at the coleptilar or scutellar stage of embryogeny. The embryos are often fused together especially at the coleorhizal end of the embryo axis. The tissue can be subcultured and maintain this morphology.

Type II callus: A type of adventive embryogenesis found with gramineous monocots, which has been induced on an explant where the somatic embryos are arrested at the globular stage of embryogeny. The globular embryos often arise individually from a common base. The tissue can be subcultured and maintain this morphology.

Variant: A culture exhibiting a stable phenotypic change whether genetic or epigenetic in origin.

Vegetative propagation: Reproduction of plants using a nonsexual process involving the culture of plant parse such as stem and leaf cuttings.

Undifferentiated: With plant cells, existing in a state of cell development characterized by isodiametric cell shape, very little or no vacuole, and a large nucleus, and exemplified by cells comprising an apical meristem or embryo. With animal cells, this is the state wherein the cell in culture lacks the specialized structure and/or function of the cell type in vivo.

Virus-free: Free from specified viruses based on tests designed to detect the presence of the organisms in question.

1. Committee on Standardized Genetic Nomenclature for Mice. 1972. Standard karyotype of the mouse, Mus musculus. J. Hered. 63:69-72.
2. Paris Conference (1971), Supplement (1975). Standardization in Human Cytogenetics. Birth Defects: Original Article Series, XI, 9, 1975. The National Foundation, New York (Reprinted in: Cytogenet. Cell Genet. 15:201-238,1975).
3. Committee for a Standardized Karyotype of Rattus norvegicus. 1973. Standard karyotype of the Norway rat, Rattus norvegicus. Cytogenet. Cell Genet. 12: 199-205.