MCF-7 passage number - (Apr/20/2010 )

I have a few questions.

I have heard that after freezing and thawing cells (say at passage 9) that MCF-7 cells sort of 'reset' back to passage 0. Is this true? I have also heard that immortal cell lines like MCF-7 can be subcultured indefinitely without any changes to the characteristics of the cells..is this true?
What are the best passage numbers for experimentation? Is it anything from passage 2 - 9? And if immortal cell lines can indeed be indefinitely subcultured, then why are these the optimal passage numbers?

Thanks in advance!

brilletjies on Apr 20 2010, 12:09 PM said:

Not true! laboratory evolution is a very real process - minor variations in your technique from those used elsewhere in the lab/country/world will result in changes in the cells over time. For example: if every time you split/lift your cells you don't quite wait for all the cells to detach, you are gradually selecting for cells that detach easily - so the time needed for trypsin to work will slowly decrease. These cells can no longer be truly called MCF-7. This is the reason it is a good idea to freeze down cells at each passage, so that you minimise the amount of change over time, without depleting the tubes that are "true" MCF-7. You can also see with careful observation cells that have been up for 10-20 passages behave differently to freshly thawed cells.

Cells do not reset back to passage 0 during freezing for the reasons above. You can also observe this in primary cells with the Hayflick limit.

The best numbers will be as low as possible as these are the most similar to the original line. However, always make sure you have some low passage number tubes in storage, so that you can take a new one out and use them for several passages before the phenotypes change.