REGENERATING (REG) AND INSULIN GENES ARE EXPRESSED IN PREPANCREATIC MOUSE EMBRYOS

The pancreatic regenerating (reg) gene is proposed to be involved in p ancreatic beta-cell growth. Up- or down-regulation of reg gene express ion has been shown to parallel variations in beta-cell mass and functi on in the adult pancreas. In several species at least two nonallelic r eg genes have been identified. In this study we investigated the expre ssion of each individual reg gene (reg-I and reg-II) during embryogene sis in the mouse. Single mouse embryos were harvested at 8.5, 9, 10, a nd 12 days of development, homogenized and subjected individually to r everse transcription (RT)-PCR, with a single primer pair to amplify bo th reg-I and -II mRNAs. Southern blot analysis of the RT-PCR products revealed the presence of reg mRNA at day 9 of embryogenesis, just befo re the beginning of pancreatic organogenesis. Slot-blot analysis with internal oligonucleotide probes that specifically recognize reg-I or - II sequences demonstrated that only reg-I mRNA was present in day 9 an d day 10 prepancreatic embryos. Reg-II mRNA was not detected until day 12, a stage corresponding to late organogenesis. RT-PCR for insulin m RNA from the same samples used for the amplification of reg mRNA showe d that the earliest insulin expression occurred at day 8.5, and coinci ded with the onset of reg-I expression. Hybridization with gene-specif ic oligonucleotide probes revealed that only insulin-II mRNA was detec table at this time. Insulin-I mRNA was not detectable until day 12 and coincided with early reg-II expression. These results suggest that th e two nonallelic reg genes and the two insulin genes are expressed dif ferentially during early embryogenesis. Differential expression of reg -I and -II suggests that they may be induced by different and independ ent stimuli and have distinct functions.