Blocking Rac1 activation results in impaired migration of β cells. Frozen sections of P3 (A,C) and adult (B,D) pancreata were stained with antibodies against the ductal marker DBA (red) and insulin (green). The endocrine clusters in the RIP-RacN17 mice (C,D) are found more closely associated with the ducts both at P3 and in the adult compared to wild-type (A,B). (E) Quantification of the percentage of islet circumference in contact with a duct at P3 shows an increase in transgenic mice compared to wild-type littermates, marking a closer association between islets and ducts in transgenic animals (n = 4). (F) Quantification of the distance between the islet and its closest duct in the adult pancreata shows a reduced distance in the transgenic animals compared to wild-type littermates (n = 4). Error bars represent standard deviation from the mean (± s.d.) and significant values are indicated as **p < 0.01 and ***p < 0.0001 determined by Student's t-test. Bars, 50 μm.