Identification of Glis1, a novel Gli-related, Kruppel-like zinc finger protein containing transactivation and repressor functions

In this study, we describe the identification and characterization of a novel Kruppel-like protein named Gli- similar 1 (Glis1). The Glis1 gene encodes an 84.3-kDa proline- rich protein. Its five tandem zinc finger motifs exhibit highest homology with those of members of the Gli and Zic subfamilies of Kruppel-like proteins. Glis1 was mapped to mouse chromosome 4C6. Northern blot analysis showed that expression of the 3.3-kb Glisl mRNA is most abundant in placenta and adult kidney and expressed at lower levels in testis. Whole mount in situ hybridization on mouse embryos demonstrated that Glisl is expressed in a temporal and spatial manner during development; expression was most prominent in several defined structures of mesodermal lineage, including craniofacial regions, branchial arches, somites, vibrissal and hair follicles, limb buds, and myotomes. Confocal microscopic analysis showed that Glis1 is localized to the nucleus. The zinc finger region plays an important role in the nuclear localization of Glis1. Electrophoretic mobility shift assays demonstrated that Glis1 is able to bind oligonucleotides containing the Gli-binding site consensus sequence GACCACCCAC. Although monohybrid analysis showed that in several cell types Glis1 was unable to induce transcription of a reporter, deletion mutant analysis revealed the presence of a strong activation function at the carboxyl terminus of Glis1. The activation through this activation function was totally suppressed by a repressor domain at its amino terminus. Constitutively active Ca2+- dependent calmodulin kinase IV enhanced Glis1-mediated transcriptional activation about 4-fold and may be mediated by phosphorylation/activation of a co-activator. Our results suggest that Glis1 may play a critical role in the control of gene expression during specific stages of embryonic development.

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