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Target Discovery and Validation Reviews and Protocols

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Keratin Transgenics <strong>and</strong> Knockouts 243<br />

4. Notes<br />

1. It is important to keep ES cell passage number as low as possible to maximize<br />

germline competence <strong>and</strong> to minimize genetic <strong>and</strong> epigenetic alterations. It is recommended<br />

to prepare a sufficiently large stock of frozen vials <strong>and</strong> to exp<strong>and</strong> a vial<br />

every time for a new experiment. In general, ES cells should be split at rates<br />

between 1:6 <strong>and</strong> 1:12. High- <strong>and</strong> low-density plating carries the risk of differentiating<br />

the cells. Their growth rate (typical doubling time is 20–22 h) should be<br />

carefully monitored; significant changes in growth rate <strong>and</strong> morphological appearance<br />

signal chromosomal alterations <strong>and</strong> preclude further use of such cells for<br />

gene-targeting experiments.<br />

2. To retain their excellent germline transmission potential, it is essential to keep passage<br />

number of HM-1 cells as low as possible. Good germline transmission rates<br />

depend on (1) media, plasticware, <strong>and</strong> so on; (2) limiting passage number; <strong>and</strong> (3)<br />

experimental skills. We use cell culture plastic from BD Biosciences, cell culture<br />

grade water, <strong>and</strong> reagents.<br />

3. More details about human <strong>and</strong> mouse keratin clusters can be found in ref. 3.<br />

Acknowledgments<br />

We thank Ursula Reuter, Silke Loch, <strong>and</strong> Claudia Wohlenberg for excellent<br />

technical assistance. Work by the authors was supported by the Deutsche<br />

Forschungsgemeinschaft, the Bundesministerium für Bildung und Forschung,<br />

<strong>and</strong> the Thyssen foundation. We apologize to those colleagues whose work has<br />

not been cited because of space restrictions.<br />

References<br />

1. Omary, M. B., Coulombe, P. A., <strong>and</strong> McLean, W. H. (2004) Intermediate filament<br />

proteins <strong>and</strong> their associated diseases. N Engl J Med 351, 2087–2100.<br />

2. Hesse, M., Magin, T. M., <strong>and</strong> Weber, K. (2001) Genes for intermediate filament<br />

proteins <strong>and</strong> the draft sequence of the human genome: novel keratin genes <strong>and</strong> a<br />

surprisingly high number of pseudogenes related to keratin genes 8 <strong>and</strong> 18. J. Cell<br />

Sci. 114, 2569–2575.<br />

3. Hesse, M., Zimek, A., Weber, K., <strong>and</strong> Magin, T. M. (2004) Comprehensive<br />

analysis of keratin gene clusters in humans <strong>and</strong> rodents. Eur. J. Cell. Biol. 83,<br />

19–26.<br />

4. Magin, T. M., Reichelt, J., <strong>and</strong> J. C. (2005) The role of keratins in epithelial homeostasis,<br />

Elias review, submitted.<br />

5. Rogers, M. A., Langbein, L., Winter, H., et al. (2001) Characterization of a cluster of<br />

human high/ultrahigh sulfur keratin-associated protein genes embedded in the type I<br />

keratin gene domain on chromosome 17q12-21. J. Biol. Chem. 276, 19,440–19,451.<br />

6. Bawden, C. S., McLaughlan, C., Nesci, A., <strong>and</strong> Rogers, G. (2001) A unique<br />

type I keratin intermediate filament gene family is abundantly expressed in the<br />

inner root sheaths of sheep <strong>and</strong> human hair follicles. J. Invest. Dermatol. 116,<br />

157–166.

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