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Fig. 3. Lack of - and ß-cell fate specification resulting in promotion of a somatostatin-producing cell destiny in Arx/Pax4 double mutant embryos. Co-staining of E12 (A,B), E15 (C-F), E18 (G-N,Q-X) and P0 (O,P) pancreas. The genotypes examined and the different antibody combinations used are indicated. A quantification of the endocrine modifications between the two genotypes, estimated using Student's t-test, is provided in percent under each set of pictures (n3, P<0.05; U, unchanged). (A,B) At E12, no alteration in the hormone-expressing cell numbers could be detected between wild type and double mutants. (C-L) A loss of mature glucagon- (C,D) and insulin- (C-J) expressing cells, and a dramatic increase in the somatostatin-producing cell content (G,H,K,L) is already obvious as soon as cells begin to express hormone; the number of Ngn3⁺ cells is not modified (C-F). Importantly, in embryos, the number of PP-expressing cells is not altered by Arx/Pax4 co-depletion (I-L). The supernumerary somatostatin-producing cells found in the double mutants do not express the PP hormone at E18 (K,L). (M-X) In Arx- and Pax4-deficient pancreas, the expression of the ß-cell-specific transcription factors Nkx6.1 and Glut2, is dramatically reduced (N,P; compare with wild type in M,O). Interestingly, the number of ghrelin-expressing cells is also reduced (R, compare with Q) and these cells produce neither somatostatin nor insulin. (S,T) Similarly, the expression of Nkx2.2 appears to be severely diminished in the double mutants; it is found in the remaining PP-cells, but is excluded from the somatostatin-producing cells (U,V). Finally, Pax6 labelling can be seen in all endocrine cells in the double mutants (W,X).

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