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Analysis of the Gene Regulatory Program Induced by the Homeobox Transcription Factor Distal-less 3 in Mouse Placenta

Department of Biomedical Sciences, Cornell University, Ithaca, New York 14853

Address all correspondence and requests for reprints to: Mark S. Roberson Ph.D., T3-004d Veterinary Research Tower, Department of Biomedical Sciences, Cornell University, Ithaca, New York 14853. E-mail: msr14{at}cornell.edu.

Dlx3, a homeodomain transcription factor, is essential for placental development in the mouse. The Dlx3^–/– mouse embryo dies at embryonic d 9.5–10 putatively due to placental failure. To develop a more comprehensive understanding of the gene profile regulated by Dlx3, microarray analysis was used to determine differences in gene expression within the placenta of Dlx3^+/+ and Dlx3^–/– mice. Array analysis revealed differential expression of 401 genes, 33 genes in which signal to log ratio values of null/wild-type were lower than –0.5 or higher than 0.5. To corroborate these findings, quantitative real-time PCR was used to confirm differential expression for 11 genes, nine of which displayed reduced expression and two with enhanced expression in the Dlx3^–/– mouse. Loss of Dlx3 resulted in a marked reduction (>60%) in mRNA expression of placental growth factor (Pgf), a member of the vascular endothelial growth factor family. Consistent with these results, Pgf secretion from placental explants tended to be reduced in the Dlx3^–/– mice, compared with wild type. To investigate mechanisms of Dlx3 regulation of Pgf gene transcription, we cloned 5.2 kb of the Pgf 5' flanking sequence for use in reporter gene assays. Expression of the Pgf promoter luciferase reporter containing at least three Dlx3 binding sites was increased markedly by overexpression of Dlx3 supporting the conclusion that Dlx3 may have a direct effect on Pgf promoter activity. These studies provide a novel view of the transcriptome regulated by Dlx3 in mouse placenta. Dlx3 is specifically required for full expression and secretion of Pgf in vivo. Moreover, in vitro studies support the conclusion that Dlx3 is sufficient to directly modulate expression of the Pgf gene promoter in placental cells.