I never specifically synchronized cells for migration assays. I just didn't use confluent cells.

Thanks for your rapid answer. I am comparing two cell lines (on is the native cell line, the other is a mutated version for a specific gene). Because of this mutation and clonal selection, these two cell lines do not have the same doubling time and I was wondering if this could be a point of criticism while comparing their migration properties. Fab

You may block cell division using mytomycin

Hi. Is the mutated cell line derived from the native cell line?

Yes it is.

Good. Is the mutated gene a knock-in?

If not, I think it will be difficult for you to state that whatever differences you observe are due solely to the mutated gene and nothing else.

I suggest to serum starve cells to synchronize them and then give them shorter migration time with higher density of cells to prevent doubling time being a factor to affect migration . for example in 4-6 hour after serum starvation count the migrating cells.

I agree with Parisa. I've always serum starved to synchronize cells and used a migration time that is shorter than their doubling time and seeding at a high density will help.

Yes, serum starve in the flask  at least 24 hours prior to seeding at a confirmed density for migration.  If you use the xCELLigence DP system with the electronic "transwell", you will be able to monitor migration continuously which enables you to calculate kinetics of migration easily without fixing, staining or counting cells.