Current Research Projects

The Sonic hedgehog / Patched / Gli Signal Transduction Pathway

We established that GLI1 protein regulates a set of genes that coordinately control proliferation and may in part explain malignant transformation by mis-expression of GLI1. Our laboratory’s research is focused on the regulation of GLI promoters and microarray studies to identify gene targets that involve transformation and oncogenesis, particularly of rhabdomyosarcoma and medulloblastoma. The interaction of GLI with other proteins and any effect such interactions might have on transcriptional regulation is not well understood. In previous work, we have made major contributions to the understanding of the Shh pathway and its role in human disease. These discoveries include identifying a range of gene targets of GLI1 important in transformation, establishing important aspects of genetic regulation of GLI1, characterizing the biochemistry of GLI1 transregulation, describing mechanisms of translational repression of GLI1 and its homologues tra-1 and tra-, and identifying the role of GLI1 and Shh in prostate development and cancer. We were the first to show that non-canonical signaling via cMyc drives GLI1 during lymphomagenesis. In addition, we have investigated haplotypes of SNPs of GLI1 demonstrating they do not predispose Caucasians to basal cell carcinoma. We were the first to clone and sequence mouse GLI1 demonstrating nearly complete sequence identity with the human gene. We were the first to establish a role in development for GLI1. We discovered the conserved 3’ UTR element for post-transcriptional regulation of GLI1 translation. We created GLI1 ectopic expression models, establishing GLI1’s role in the GI tract and testes. We isolated human GLI1, and were the first to establish its genomic organization and to map the human GLI1 promoter. We proved that GLI1 is a transcription activator; we established an N-terminal negative modulator and further established that GLI1 could also repress genes. We were the first to establish that GLI1 contained a VP16 like domain that is necessary and sufficient for transactivation. We established co-localization of GLI1 with tubulin in mammalian cells along the mitotic spindle. However, significant unanswered questions remain including how GLI1 regulates key gene targets. In order to achieve this regulation, GLI1 must recruit a complex to the gene target and we propose to investigate those proteins. The protein complex requires that GLI1 bind to the target DNA yet despite a structural solution to the binding domain and a consensus DNA binding sequence little is known of what modulates the binding and its effect. We propose to develop a model of differential target binding.  Read more about the Shh/Patched/Gli signal transduction pathway.

Regulation of GLI1 Transcription

GLI1 has a complex transcriptional regulatory domain. The function of the human GLI1 promoter is conserved in transgenic mice.

Translational Regulation of GLI

Post-transcriptional regulation of protein levels of GLI1 occur via the 3’ UTR of the human gene and this is an active area of research in our lab. The 3’ UTR contains domains that bind translational repressors. Photomicrographs of transgenic C. elegans reporter expression is enhanced by deletion of the 3’ UTR of both tra-2, tra-1 (worm genes) and GLI1 (human gene) indicating that translational regulation is occurring through this region. We showed the translational repressors were gld-1  in the worm and Qk in human.

Genes Transcriptionally Regulated by GLI1

As a transcription factor that controls the expression of other genes and as an oncogene GLI1 regulates genes causing malignant transformation, both its onset and its maintenance. For cancer to be a problematic maintenance of the transformed phenotype is necessary. We used high-throughput gene expression profiling to establish some of the genes that GLI1 regulates as part of the transformation process. We have demonstrated non-canonical activation of GLI1 through c-myc is an important feature of lymphogenesis. GLI1 is a human oncogene that functions during development in a molecular pathway specifying morphogenesis of many organ systems including the brain, lung, GI system and the prostate. Given the importance of disease consequences of GLI1 mis-expression we need to understand what regulates its expression. Read more about GLI1 transcriptionally regulated genes.

Mosaic Pattern Analysis in Chimeras: An Approach to Tissue Growth

The term “chimera” is used to describe, in our case, animals that have been constructed to include genetic lineages from two different strains of animals. For example, by taking an 8-cell stage embryo from a black rat and another from a white rat, and combining them to produce an aggregate embryo and place it in a surrogate mother, the offspring will present features of the two different colored rats. These multizygotic mosaic animal offspring are called chimeric animals. The zebra-like patches of fur on the chimeric rats are the most obvious sign of feature blending. With appropriate markers, patches are also visible in the animal’s organ tissue, like the adrenal gland, liver and corneas. The patterns exhibited in tissues of chimeras could be explained by recursive and iterated cell division schemes. These schemes can then be represented with computer models. Based on this information the lab’s goals are to firmly establish a 3-D volumetric representation of the patch geometry in the chimera’s tissue, robust computer models which are predictive of patch tissue growth, and a volume based analysis of the fractal dimension of the patch tissue. We recently demonstrated that cornea superficial epithelial cell assortment occurs in response to global biomaterial properties of the cornea structure and intraocular pressure forming pinwheel patterns of mathematically definable spirals. We are working to refine the bioengineering models and data acquisition process from novel forms of genetic mosaics. By carefully characterizing the spiral curves that occur at the boundaries of patches of distinguishable cell lineages (patches) we can determine the validity of the models and gain insight to structural properties important in the normal cornea. This work was recently published in Biomechanics and Modeling in Mechanobiology. These data will help to advance the generation of bioengineered corneas.