The purpose of this experiment was to assess global changes in gene expression pattern in the pancreas from Sox4-/- embryos vs. pancreas from Sox4 wild-type embryos at embryonic day 12.5. [Sox4 gene knock-out (Schilham, M. W. et al. (1996) Defects in cardiac outflow tract formation and pro-B-lymphocyte expansion in mice lacking Sox-4. Nature 380, 711-4.)]

Investigate the role of Sox transcription factors in the development of the pancreas.

Temporal expression (e10.5 - e16.5) of Sox factors were followed using TaqMan RT-PCR. Sox2 and sox4 were investigated further. Sox2-lacZ knock-in mice were harvested (e9.5, e10.5, e16.5) and stained for beta-galactosidase actvitiy and for pdx1. Sox4 expression was monitored in adult mice by in situ hybridization and immunofluorescent staining. Developing pancreas was examined up to e12.5 in Sox4 -/- mice by morphology and immunohistochemical staining; pancreatic explants from e11.5 were used to follow further development. Microarrays based on the FANTOM1 clone set and selected additional clones were hybridized with labeled amplified RNA from separate pools of sox4-/- and sox4+/+ pancreatic buds (2 each from 3 independent amplifications).

Sox 2, 11, and 12 mRNAs were found at e10.5 but then declined with modest levels of sox12 persisting in islets. Sox4 and sox9 had peaks after the secondary transition (e13) and sox4 and sox13 mRNA levels were high in islets. Sox2 expression was specifically excluded from the pancreatic buds. In contrast, Sox4 was detected broadly in the early pancreatic buds and eventually became restricted to the nuclei of all islet cells in the adult mouse. Microarray studies detected reduction in sox4-/- pancreatic buds for both ins1 and ins2, Nkx6.1, peroxiredoxin 2, and glutathione peroxidase 1 mRNAs. Increases were found in the mutants for Sox11, Neurogenin3, and NeuroD1 mRNAs.

Sox2-expressing stems cells are rare or do not exist in the mouse pancreas. By contrast, Sox4 is required for the proper expansion of the endocrine cell population, especially beta cells, after the secondary transition.

• islet morphology: 2944, 3386,