Fig. 1. Increase in the population of somatostatin- or PP-producing cells at the expense of insulin- and glucagon-expressing cells in Arx/Pax4 double-mutant pancreas. Sections of P2 mice were examined for pancreatic hormones in wild-type (A-I), Arx/Pax4 double-heterozygous (J-R) and Arx/Pax4 double-deficient (S-Z2) animals by co-immunofluorescence. Islets were stained with antibodies directed against insulin (A-C,J-L,S-U), and antibodies recognizing either glucagon- (D,M,V), somatostatin- (E,N,W) or PP-producing cells (F,O,X), and sections were counter-stained with DAPI (merged in G-I,P-R,Y-Z2). Note the loss of the insulin- (A-C,S-U) and glucagon- (D,V) producing cell population, and the dramatic increase of the somatostatin- (E,W) or PP- (F,X) expressing cell numbers in the double mutants. The simultaneous lack of a single Arx and Pax4 allele does not provoke any significant endocrine alteration when compared with wild-type animals (A-I,J-R).