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Target Discovery and Validation Reviews and Protocols

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232 Vijayaraj, Söhl, <strong>and</strong> Magin<br />

3. http://genetics.med.harvard.edu/~dymecki/.<br />

4. http://www.ensembl.org/Mus_musculus/.<br />

2.2.2. Tables<br />

Conditional alleles in mice: tissue-specific knockouts, kkwan@mail.<br />

md<strong>and</strong>erson.org.<br />

2.2.3. Vendors<br />

1. http://www.invitrogen.com/.<br />

2. http://www.sigmaaldrich.com.<br />

3. http://www.rndsystems.com/.<br />

4. www.calbiochem.com.<br />

2.2.4. Vectors<br />

1. http://www.aldevron.com/vectors.php?vid=5.<br />

2. http://www.stratagene.com/lit/vector.aspx.<br />

3. http://www.genome.gov/10001852.<br />

4. Mutant Lox P vectors, hiroshi@genetics.hpi-uni-hamburg.de.<br />

3. Methods<br />

3.1. Routine Culture, Generation, <strong>and</strong> Characterization<br />

of Genetically Altered Mouse ES Cells<br />

Here, we describe culture of HM-1 cells, which are derived from the mouse<br />

strain 129/Ola <strong>and</strong> are HPRT-deficient. They are grown feeder-free <strong>and</strong> in gelatinized<br />

dishes. Other feeder-independent ES cell lines are grown essentially in<br />

the same way. For routine culture, cells should be passaged twice a week, splitting<br />

them between 1:6 <strong>and</strong> 1:12, depending on conditions. They should not<br />

be plated too thin because thin plating encourages excessive differentiation.<br />

Overconfluent cultures should be avoided for the same reason. Medium change<br />

should take place every other day as long as the culture is thin; later, medium<br />

should be changed every day. Any drastic change in cell doubling times or cell<br />

morphology is indicative of unwanted damage to the cells, e.g., chromosomal<br />

aberrations (see Note 2). Typical doubling time is approx 20–22 h (see Fig. 5).<br />

3.2. Thawing <strong>and</strong> Plating Cells<br />

1. Gelatinize flask by using enough gelatin to completely cover the flask or dish.<br />

2. Leave at room temperature (RT) for at least 10 min. Aspirate off before plating cells.<br />

3. If feeders are used, plate appropriate amount of cells together with ES cells or<br />

plate them 3 to 4 h earlier. Feeder-coated dishes can be used up to 7–10 d. Check<br />

for integrity of monolayer before using them to plate ES cells.<br />

4. Thaw cells quickly in 37°C bath <strong>and</strong> transfer into 10-mL prewarmed medium.<br />

Spin for 5 min at 250g.

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