Patricia and Megan to present at Student Seminar Thursday (28.Jan) at noon in 106 BBE
Background for Patricia’s talk
Wnt ligands have pleiotropic effects during development, consequently, multiple negative regulators function to precisely control Wnt activity. While many genes such as DKK, Axin and Naked are induced by Wnt/β-catenin to negatively regulate β-catenin stabilization, the integration of signals from different arms of the Wnt network, potentially regulated by different classes of Wnt ligands, is emerging as an equally important control mechanism. I have a special interest in understanding how Wnt signaling controls the formation of the embryonic axis in vertebrates. I use zebrafish and Xenopus laevis to unravel the mechanisms behind axis formation. In our lab, we utilize gene knockdown as well as transgenic lines to dissect the function of members of this signaling pathway during embryonic stages.
Project 1. Axin is a key player in the degradation complex, as it serves as the scaffold for proteins involved in the phosphorylation of β-catenin. Axin contains four critical domains: a β-catenin binding domain, a GSK3 binding domain, a Regulator of G-protein (RGS) domain and a DIX domain (protein interaction domain shared with Dsh). RGS domains are typical of RGS proteins, which were originally identified as regulators of the active half-life of G-protein signaling. However, it is not known whether the Axin-RGS domain functions in G-protein signaling. My work focuses on the function of the Axin-RGS domain during maternal and zygotic stages.
Project 2. The means by which Wnt/Ca2+ signaling negatively regulates the Wnt/β-catenin signaling is unknown, but it likely requires a Ca2+ sensor protein. Among candidate mediators, Nkd displays the distinctive property of affecting both β-catenin-dependent and -independent arms of the Wnt signaling network. Nkd functions as a Wnt/Wg antagonist by binding to the basic/PDZ domain of Dvl. Vertebrate Nkd overexpression results in convergence and extension (CE) movement defects.
Whereas the precise mechanism underlying Nkd-mediated Wnt antagonism is unresolved, it is well established that Nkd interacts with Dvl and impacts β-catenin-dependent and -independent Wnt signaling networks. My focus on this project is to understand the role of the NKD cuticle during axis formation and how this protein functions in the context of β-catenin stabilization.
Background for Megan’s talk
Otosclerosis has a prevalence of 0.2 – 1% among white adults making it the single most common cause of hearing impairment in persons of northern European ancestry. Histologically, it is characterized by the replacement of discrete areas of endochondral bone in the otic capsule by otosclerotic bone. We have shown that a large number of genes are differentially expressed in otosclerotic stapes footplate samples as compared to normal footplate samples. To identify small molecules that may be potentially useful to treat otosclerosis, we have compared our expression data to the Connectivity Map (cmap) provided by the Broad Institute. This resource allows the user to compare gene expression data in a biological sample/disease with 7,000 expression profiles from 1,309 different small molecules. Negative connectivity of a query profile with cmap data can be used to test specific small molecules that might be therapeutically important based on the disease profile.
Arachidonic acid has the best negative connectivity compared to otosclerosis expression data across all instances (cell lines and doses tested for the cmap project) (p=0.00018). When genes involved in inflammation or interleukin signaling are removed from the otosclerosis expression data and the Connectivity Map is re-queried, arachidonic retains the best negative connectivity (p=0.0002). These findings are noteworthy because arachidonic acid increases osteoclastogenesis by reducing the OPG/RANKL ratio secreted by osteoblasts and is converted to PGE2; PGE2 signaling affects BMP2 expression; and BMP2 is associated with otosclerosis.
In addition to BMP2, TGF-β1 and BMP4 have been shown to be associated with otosclerosis. TGF-β1, BMP2 and BMP4 are present in the otospongiotic phase of otosclerosis as are their receptors. We have failed to replicate these associations in a German population, however, lack of power and differences in LD may account for lack of replication. Rather than looking for common variants associated with otosclerosis in this population, we are testing the common disease-rare variant hypothesis, by sequencing TGF-β1, BMP2 and BMP4 in >250 German patients with otosclerosis and in 250 matched controls. We have found a number of variants that will be used for further functional studies including affects on osteoclast and osteoblast function in the presence of arachidonic acid.