What is Tissue Culture?
Tissue culture is a biological research method in which tissue pieces of animals and plants are transferred to an artificial environment to survive and function. Cultured tissue can consist of a single cell, group of cells, or all or part of an organ. Cells in culture can proliferate. Changes in size, morphology, or function; exhibiting special activity (eg, muscle cells can contract) or interacting with other cells.
Historical Developments in 1885
In 1885, German zoologist Wilhelm Roux attempted tissue culture early. He cultured the tissue from chicken embryos in a warm salt solution. However, the first real success was in 1907, when American zoologist Ross G. Harrison showed the growth of frog neuronal processes in the coagulation of lymph. Later, French surgeon Alexis Carrel and his assistant Montrose Burrows improved Harrison’s technique and reported their first progress in a series of treatises published in 1910-11. Carrel and Burroughs coined the term tissue culture and defined this concept.
Since then, many experimenters have succeeded in using a variety of body fluids (lymph, serum, plasma, tissue extracts, etc.) as media for culturing animal cells. In the 1980s and 1990s, various methods were developed to enable researchers to successfully culture mammalian embryonic stem cells under artificial conditions. These breakthroughs ultimately enabled the establishment and maintenance of human embryonic stem cell lines, facilitated researchers’ understanding of human biology, and significantly facilitated advances in therapeutic and regenerative medicine.
Cells can grow in biologically induced media such as serum or tissue extracts, chemically defined synthetic media, or a mixture of the two. The medium should contain the proper proportions of nutrients needed by the cells under study and should be properly acidic or alkaline. Cultures typically grow as a monolayer of cells on a glass or plastic surface, or as a suspension in a liquid or semi-solid medium.
To start culturing, disperse a small portion of the tissue sample on or in the medium and incubate the culture flask, tube, or culture plate at a temperature usually close to the normal environment of the tissue. Keep sterile to prevent microbial contamination. Cultures may begin with a single cell, resulting in a unified biological population called a clone. Single cells usually colonize within 10-14 days under culture conditions.
Primary Cultures And Established Cell Lines
There are two main types of culture. Primary (lethal) culture and established (immortal) cell line culture. Primary cultures consist of normal cells, tissues, or organs that have been resected directly from biopsy-collected tissue. Primary culture is advantageous because it basically mimics the natural function of the cell, tissue, or organ under study. However, the longer the sample is cultured, the more mutations will accumulate in the sample, which can lead to changes in chromosomal structure and cell function.
In addition, Aboriginal culture is usually deadly. Because cells go through an aging process, they can only proliferate for 50 to 100 generations, after which they slow down significantly. The point at which cells in primary culture stop growing or undergo replication aging indicates the so-called Hayflick limit (named after its discoverer, American microbiologist Leonard Hayflick).
In contrast, established cell lines can continue indefinitely. Such cell lines can usually be derived from a patient’s tumor biopsy or can be generated from mutated primary cells that allow Hayflick limits to be overcome and replication to continue. Like cells in primary culture, cells of established lineage can accumulate mutations over time, which can change their properties. Therefore, in order for researchers in different laboratories to compare the results of experiments using the same cell line, it is necessary to confirm the identity of the cells used. Cell identity is verified through a process called validation in which the DNA profile of cultured cells is compared to a known or standard profile of the cell line.
Processing Of Cultured Cells And Tissues
Living cultures can be examined directly under a microscope or observed in photographs or movies taken under a microscope. Cells, tissues, and organs can also be killed, fixed (preserved), and stained for further examination. After fixation, the sample can be embedded (for example, in resin) and cut into thin slices to reveal other details under a light microscope or electron microscope.
Cells in tissue culture undergo extensive experimental processing. For example, viruses, drugs, hormones, vitamins, pathogenic microorganisms, or chemicals suspected of being carcinogenic can be added to the culture. Scientists then look at cells for changes in specific molecules, such as overall changes in cell behavior or function, or changes in the expression of specific proteins or genes.