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Figure 2: Pax4 and Arx are necessary and sufficient to promote the beta- and alpha-cell fate/identity, respectively. Schematic describing the strategy used to conditionally force the expression of Pax4 or Arx in the pancreatic endoderm, in endocrine cells or in alpha- or beta cells, depending on the promoter used to drive the expression of the Cre recombinase. (1) Transgenic mice carrying a construct allowing the conditional activation of Pax4 or Arx expression under the control of beta-actin/CMV (promoter/Enhancer) display ubiquitous green fluorescent protein (GFP) expression. LoxP (L) sites (black bars) flanking GFP coding sequences and a stop codon allowing the activation of Pax4 or Arx only following the crossing of these mice with transgenic mice expressing the Cre recombinase under the control of pancreatic promoters (2) (Table 1). Double transgenic mice carrying the constructs (1) and (2) will undergo Cre-induced homologous recombination to express Pax4 or Arx in conjunction with the marker LacZ ((3) and (4)), allowing the tracing of Pax4-expressing cells.