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I'm translating one Russian text where a cell line is transfected to produce a drug. I wonder if I can sometimes use "cell strain" or simply "strain" instead of "cell line" or instead of "producer" (продуцент, meaning "the producer of the drug", i.e. the cells that produce the drug).

I googled and found this answer on Yahoo answers:

Cells in culture can be passaged a finite number of times before reaching a crisis which can be compared with aging. The number of passages, before reaching crisis, has been termed the Hayflick limit and is related to the longevity of the species from which the tissue was originally derived.

Within the Hayflick limit, the cells are referred to as a cell strain.

Cells that survive the crisis and continue to grow are referred to as a cell line. Cell lines can also be derived directly from cancer cells. There are many properties that distinguish cell lines from cell strains, including altered chromosome number, changes at the cell membrane, and reduced requirement for certain growth factors.

Therefore:

A cell strain is defined as an euploid population of cells subcultivated once or twice in vitro, lacking the property of indefinite serial passage. Cell strains ultimately undergo degeration or death (senescence). A cell line is an aneuploid population of cells that can be grown in cultures indefinitely.

Is this true? Is a cell line always aneuploid and capable of indefinite growth, as opposed to being euploid and incapable of indefinite growth?

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"Strain", in general, is usually used for whole organisms (whether they are unicellular or multicellular). For example, there are mouse strains.

"Cell line", on the other hand, is a very specific term that is used to refer cultured cells obtained from a multicellular organism. They need not be necessarily aneuploid.

Is a cell line always aneuploid and capable of indefinite growth, as opposed to being euploid and incapable of indefinite growth?

Aneuploidy does not have any causative relationship with indefinite growth. Most cancerous cells evade the cell cycle checkpoints, which allows them to grow out of control. Some of these checkpoints also ensure proper segregation of chromosomes. Bypassing them leads to aneuploidy.

Are cell lines essentially immortal?

Usually primary cell cultures are not referred to as "cell lines" these days. However, originally, any cultured cell that grows in vitro is called cell line. From Freshney (Basic Principles of Cell Culture):

When cells are isolated from donor tissue, they may be maintained in a number of different ways. A simple small fragment of tissue that adheres to the growth surface, either spontaneously or aided by mechanical means, a plasma clot, or an extracellular matrix constituent, such as collagen, will usually give rise to an outgrowth of cells. This type of culture is known as a primary explant, and the cells migrating out are known as the outgrowth (Figs. 1.1, 1.2, See Color Plate 1). Cells in the outgrowth are selected, in the first instance, by their ability to migrate from the explant and subsequently, if subcultured, by their ability to proliferate. When a tissue sample is disaggregated, either mechanically or enzymatically (See Fig. 1.1), the suspension of cells and small aggregates that is generated will contain a proportion of cells capable of attachment to a solid substrate, forming a monolayer. Those cells within the monolayer that are capable of proliferation will then be selected at the first subculture and, as with the outgrowth from a primary explant, may give rise to a cell line.

Elsewhere, a cell strain is defined as positively selected subpopulation of cells:

A cell strain is a subpopulation of a cell line that has been positively selected from the culture, by cloning or some other method. A cell strain will often have undergone additional genetic changes since the initiation of the parent line. Individual cell strains may, for example, have become more or less tumorigenic than the established line, or they may be designated as a separate strain following transfection procedures.

This definition does not say anything about what kind of selection was used. You can select for cell that express GFP, for instance. So that strain would be simply designated as GFP+.

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