These cells are isolated from the distal region of the E10.5 forelimb bud. These cells are isolated by microdissection of the E10.5 forelimb. After proteolytic digestion, cells are filtered through a cell strainer to obtain a single-cell suspension and then resuspended at a density of 2x10^7 cells/ml. Then, five 10 μl aliquots of this suspension are plated into a 35 mm tissue-culture dish and allowed to adhere for 1 hour. Following this period, 2 ml culture medium are added to each well.