Plant and Mammalian Tissue Culture Mammalian Cell Culture
Tissue Culture • Tissue Culture: • The general term for the removal of cells, tissues or organs from an animal or plant and their subsequent placement into an artificial environment conducive to growth. • Can be used to prepare finite or continuous cell cultures • Will be similar biochemically and physiologically to parent tissue
Organ Culture • Organ Culture • The culture of whole organs or intact organ fragments with the intent of studying their continued function or development. • Can be maintained for hours or days by perfusion with oxygenated blood or serum. • Used for metabolism and drug studies • Provides most accurate reflection of organism’s physiology
Organ Culture • Organ Culture • U of Minnesota 2007 – heart perfusion w/stem cells created a “new heart”. (Click here for movie)
Cell Culture • Cell Culture • When cells are removed from the organ fragments prior to, or during cultivation, thus disrupting their normal relationships with neighboring cells. • General term explaining non-”in vivo” experiments • Non-tissue growth of plant and animal cells
Mammalian Cell Culture • Mammalian Cell Culture • Cell culture of mammalian cells. • Eukaryotic cells are much more difficult to culture than most prokaryotes. • They demand complex media • They are very susceptible to contamination and overgrowth by microbes such as bacteria, yeasts and fungi.
Cell Culture • Two types of cell culture • Primary Culture • Cell Line Culture • AKA – finite / continuous / established / secondary / subclone / immortalized cell culture
Primary Culture Come from the outgrowth of migrating cells from a piece of tissue or from tissue that is disaggregated by enzymatic, chemical, or mechanical methods. Formed from cells that survive the disaggregation process, attach to the cell culture vessel (or survive in suspension), and proliferate.
Primary Culture Primary cells are morphologically similar to the parent tissue. These cultures are capable of only a limited number of cell divisions, after which they enter a nonproliferative state called senescence and eventually die out.
Primary Culture Primary cells are considered by many researchers to be more physiologically similar to in vivo cells. Primary cell culture is generally more difficult than culture of continuous cell lines.
Primary Culture • Advantages • They are thought to represent the best experimental models for in vivo situations. • Have the same karyotype as the parent tissue normal or abnormal. • Not “dedifferentiated” • Disadvantages • Difficult to obtain. • Relatively short life span in culture. • Very susceptible to contamination • May not fully act like tissue due to complexity of media • Considerable variation in population and between preparations
Primary Culture • Tumor Primary Cell Culture • Easier to create as tumors cell cycle / growth regulators have been altered • Tumor cells often produce own growth factors (autocrine) • Mechanically disrupted tissue easily plates, binds and can thrive • Seeding density often must be high for primary culture of tumors.
Finite Cell Lines • AKA – secondary or subclone culture • Finite cell cultures are formed after the first subculturing (passaging) of a primary cell culture. • These cultures will proliferate for a limited number of cell divisions, after which they will senesce. • The factors which control the replication of such cells in vitro are related to the degree of differentiation of the cell
Finite Cell Lines The cells will proliferate for an extended time, but usually the culture will eventually cease dividing, similar to senescent primary cells. Use of such cells is sometimes easier than use of primary cell cultures, especially for generation of stably transfected clones.
Finite Cell Lines • MRC5 cells • Human embryonic lung fibroblasts • Undergo between 60-70 doublings before senescence.
Finite Cell Lines • Advantages • Can obtain a large population of similar cells. • Most cellular characteristics are maintained • Can transform cells to grow indefinatly • Disadvantages • Cells have a tendency to differentiate over time in culture. • Over time the culture tends to select for aberrant cell
Continuous Cell Line • A cell line that has demonstrated the potential to be subcultured indefinitely. • Infinite cell line • Immortal cells line • Immortalized cell lines are also known as transformed cells: • Cells whose growth properties have been altered.
Continuous Cell Line Finite cell cultures will eventually either die out or acquire a stable, heritable mutation that gives rise to a continuous cell line that is capable of unlimited proliferative potential. This alteration is commonly known as in vitro transformation or immortalization and frequently correlates with tumorigenicity.
Continuous Cell Line Continuous cell lines are generally easier to work with than primary or finite cell cultures. These cells have undergone genetic alterations and their behavior in vitro may not represent the in vivo situation.
HeLa Cells • Classic example of an immortalized cell line. • These are human epithelial cells from a fatal cervical carcinoma transformed by human papillomavirus 18 (HPV18).
Continuous Cell Line • Advantages • Easy to maintain in culture. • Easy to obtain large population of cells. • Typically easy to manipulate gene expression. • Disadvantages • The more aggressive the cell line the more it changes over time in culture. • Not clear how the function of these cells relates to that of other cells, healthy or diseased.
Transformed Cells • Transformed, Infinite or Established Cells • Changed from normal cells to cells with many of the properties of cancer cells. • Some of these cell lines have actually been derived from tumors or are transformed spontaneously in culture by mutations. • Chemical or gamma ray treated cells can become infinite with loss of growth factors • Viral infection with SV40 T antigen can insert oncogenes and lead to p58 and RB gene alteration • No matter how transformation occurred, the result is a cell with altered functional, morphological, and growth characteristics.
Know Your Cells The more you know about the cells and the more finely attuned you are to the cell’s quirks, the quicker and more clear the interpretation of results will be.
Know Your Cells • The more differentiated the cell line, the slower it will grow. Categories of cell cultures based on origins.
Know Your Cells Adherent or monolayer cells – must bind to solid surface to survive and propagate. Suspension cells – may need stirring or simply placed in flask.
Know Your Cells • Adherently cultured transformed cells are usually highly anchorage-independent and adhere lightly even to tissue culture dishes. Wash these cells very carefully, as the loose monolayer can be inadvertently aspirated away.
Characterization by Cell Growth Anchorage-Independent Attachment Cultures • To survive and grow, most cells require a surface to which they can attach • Without the surface attachment these cells cannot survive • Do not require attachment for cell proliferation • Growth of cells in tissue culture dishes looks more haphazard than the growth of anchorage dependent cells with cells only loosely attached to the surface.
Characterization by Cell Growth The advantages of adherent growth is the ability of the cells to adhere and spread on surfaces such as coverslips, making microscopy, hydribidizations, and functional assays more easily performed.
Characterization by Cell Growth • Suspension CulturesSome cells can survive and divide while being suspended in a fluid media and stirred or shaken. • Flasks • Spinner Cultures • Shaker Cultures • A limited number of cell types can be maintained and grown in either format.
Characterization by Cell Growth The advantages of suspension growth are the large numbers of cells that can be achieved, and the ease of harvesting.
Place cells in a culture dish. Give them nutrients, growth factors, keep them free from bacterial. Cells will grow to cover the surface of the dish. Can take cells out of this culture and start a new culture. Splitting cells from one dish to another is a passage. Growing Cells in Culture
Number of Cell Divisions • This ability to split cells and have them continue to divide is not without limits however. • Normal cells have a limit to the number of times which they can be passed in culture. • This number does vary from cell type to cell type, but commonly the limit is between 40 and 60 passages.
Cells will continue to grow and divide normally for a limited number of passages When they get to a certain point even if they are given the appropriate nutrients, they simply stop dividing and will eventually die. Cell Number Passage Number Hayflick’s Phenomenon
There appears to be a correlation between the maximal number of passages and aging. The number of passages decreases when cells are harvested from older individuals. 70 Passes 0 -0.5 100 Age (years) Hayflick’s Phenomenon and Aging
A collection of defects which causes premature aging. Genetic disorder which causes physical symptoms like gray hair, wrinkled skin, hair loss, muscle degeneration. Child of age 4 or 5 appears like they are 80. Cells from these individuals show dramatically decreased passage number. Progeria
The phenomenon observed in normal animal cells that causes them to stop dividing when they come into contact with one another. Cells in a culture flask with the appropriate nutrients and the cells grow and divide. Continues until the cells are covering the entire surface. At that point they stop dividing. Contact Inhibition
These cells can be triggered to begin dividing again by giving them more room. The cells now being in an environment where they are not in contact with one another begin to divide again. Contact Inhibition
Passage Number and Cancer • Cancer cells appear to be immortal. • In the early 1950’s cervical cancer cells were removed from a woman. • HeLa cells. • Helen Lang, Henrietta Lack. • These cells have been grown in culture and used extensively in science. • HeLa cells have been passed well over 1,000 times and show no sign of slowing their grow rate.
Cancer cells do not display contact inhibition. Put them in a culture dish, they will grow to create a single layer of cells Then they will continue to grow multiple layers and create piles of cells. Contact Inhibition
Eukaryotic cells in attachment culture have a characteristic growth cycle similar to bacteria. The growth cycle is typically divided into three phases. Lag Phase Log Phase Plateau Phase GROWTH CYCLE IN ATTACHEMENT CULTURE
GROWTH CYCLE IN ATTACHEMENT CULTURE Subculture Plateau Phase Feed Lag Phase
Lag Phase • This is the time following subculture and reseeding during which there is little evidence of an increase in cell number. • It is a period of adaptation during which the cell replaces elements of the glycocalyx lost during trypsinization, attaches to the substrate, and spreads out. • During spreading the cytoskeleton reappears and its reappearance is probably an integral part of the spreading process.
Log Phase • This is the period of exponential increase in cell number following the lag period and terminating one or two doublings after confluence is reached. • The length of the log phase depends on the seeding density, the growth rate of the cells, and the density at which cell proliferation is inhibited by density. • In the log phase the growth fraction is high (usually 90%-100%) and the culture is in its most reproducible form.
Log Phase • It is the optimal time for sampling since the population is at its most uniform and viability is high. • The cells are, however, randomly distributed in the cell cycle and, for some purposes, may need to be synchronized.
Plateau Phase • Toward the end of the log phase, the culture becomes confluent • All the available growth surface is occupied and all the cells are in contact with surrounding cells. • Following confluence the growth rate of the culture is reduced, and in some cases, cell proliferation ceases almost completely after one or two further population doublings.
Plateau Phase • At this stage, the culture enters the plateau (or stationary) phase, and the growth fraction falls to between 0 and 10%. • There may be a relative increase in the synthesis of specialized versus structural proteins and the constitution and charge of the cell surface may be changed.
The dilemma – passage number or how long can I use these cells? High number of subculturing will change cell biochemical and molecular properties, morphology, response to agonists, growth rates and other responses May be a cell response to changed conditions from tissue When doubling times significantly change, you may check other functions of the cells to see if these are now a “different strain” than you started with.