General and Tissue Specific Gene Regulation by the WNT Signaling Pathway in Drosophila.

[摘要] Secreted proteins of the Wnt family act through a conserved signaling cascade to regulate gene expression.While many genes are regulated by this pathway in a cell-specific manner, some targets are ubiquitously activated.This thesis explores both modes of regulation by Wnt signaling using the fruit fly, Drosophila melanogaster as a model.The naked cuticle (nkd) gene is activated by Wnt signaling in all tissues examined and encodes a feedback antagonist of the pathway.To learn more about its activation by Wg, we identified several cis-regulatory Wg response elements (WREs) in the nkd locus.These nkd-WREs, two from the upstream intergenic region and another from the first intron of the nkd gene, are named UpE1, UpE2 and IntE, respectively.When the three WREs are tested simultaneously in flies, they largely recapitulate the pattern of endogenous nkd in multiple tissues.The individual WREs show distinct but overlapping patterns in various tissues.These data suggest that nkd requires multiple tissue-specific WREs to fully respond to the Wg signal.The importance of the WREs was confirmed by generating flies with a deletion in these elements, which significantly reduces the expression of nkd in several tissues. To explore the mechanism of gene-specific regulation by Wnt signaling, I characterized two related nuclear proteins, Split ends (Spen) and Spenito (Nito).Spen was previously shown to be required for regulation of some Wnt targets but the role of Nito had not been explored.I found that simultaneous depletion of spen and nito by RNA interference resulted in a greater reduction in activation of some Wnt targets than knockdown of either gene alone.This suggests that Spen and Nito act redundantly in Wnt signaling.Even with simultaneous knockdown of spen and nito, several Wnt targets are still activated normally.Biochemical analysis in cultured cells indicates that Spen and Nito are not required for formation of the TCF-Armadillo complex that is known to activate target gene expression.These data indicate that Spen and Nito are gene-specific regulators of the pathway that act downstream of TCF-Armadillo.

[发布机构] University of Michigan

[效力级别] Wg

[关键词] Wnt;Wg;Spenito;Naked Cuticle;Molecular;Cellular and Developmental Biology;Science;Molecular, Cellular, and Developmental Biology