Method of synchronizing epithelial cells into G.sub.0 phase

A method of culturing epithelial cells, comprising:

• culturing said cells in a growth medium until they reach confluence;
• removing said growth medium;
• adding a serum restricted medium, said serum-restricted medium having a concentration of serum of 5% or less;
• growing said epithelial cells in said serum-restricted medium for five days without replacing the medium, thereby producing G.sub.0 phase synchronized cells;
• and
• culturing said G.sub.0 phase synchronized cells.

A method of screening for a factor related to differentiation and/or maturation of cells, comprising:

• culturing cells in a growth medium until they reach confluence;
• removing said growth medium;
• adding a serum-restricted medium, said serum-restricted medium having a concentration of serum of 5% or less;
• growing said epithelial cells in said serum-restricted medium for five days without replacing the medium, thereby producing G.sub.0 phase synchronized cells;
• adding a candidate factor to said G.sub.0 phase synchronized cells;
• and
• determining whether said cells differentiate and/or mature.