The purpose of this research is to investigate the molecular basis of birth defects, characteristic of diabetic embryopathy, resulting from maternal diabetes using an Islet-1 (Isl-1) transgenic mouse model. Expression of the transcription factor lsl-l is necessary for normal pancreatic development. We found that dysreguIation of Isl-1 causes sacral/caudal agenesis similar to human dIabetic embryopathy. These results suggest that embryonic lsl-1 expression may be dysregulated in diabetic pregnancies. The Isl-1 transgenic mouse model, therefore provides a suitable model for studying the genetic response and will be utilized to elucidate the molecular pathways and possible biological/transcriptional targets downstream of Is!-!. Using a binary transgenic mouse model to generate IsI- I transgenics. we have control over incremental differences in gene dosage, dependent on whether the embryo is hemizygous or homozygous for the transactivator or transresponder gene. This allows us to identify transcriptional targets of Isl-1 by focusing on two parameters, gene dosage and developmental tune point (E8.5-E 12.5).
Three specific aims will be pursued: I) Evaluation of candidate lsl-1 targets using quantitative RT-PCR and in situ hybridizations. 2) Identification of new Isl-1 targets by gene expression profiling. The 15K mouse developmental gene cDNA collection and an interpretation framework specifically designed for this project will be used. in particular. microarray analysis of transgenics with high gene dosage. resulting in a more severe phenotype, will help identify compulsory target genes to the defect. 3) Gene expression studies on candidate and new Isl-l targets will be used to compare the developmental defects in lsl-1 transgenics to chemically (Alloxan) induced diabetic embrvopathies. Comparison of the genetic and the pharmacological mode! will determine whether developmental defects in diabetic embryopathv and in our Isl-1 transgenic model arise through common molecular perturbations. This study will elucidate the molecular pathways leading to sacral/caudal agenesis. The information may be further used to devise treatment strategies for diabetic mothers during pregnancy to offset the molecular changes that Lead to diabetic embrvopathies and to reduce newborn morbidity due to the developmental defect.
