Ralph Hazlewood and Xitiz Chamling will present their research on 15th Nov 2012

Ralph Hazlewood presentation abstract

Identification and characterization of genetic factors responsible for cavitary optic disc anomalies

Excavation of the optic disc leading to retinal ganglion cell death is a chief feature of optic nerve disease and blindness. Although risk factors for optic nerve diseases are known, such as the elevated intraocular pressure (IOP) observed in some glaucoma subjects, the molecular events of optic nerve degenerations are poorly understood. Patients with congenital malformations collectively called cavitary optic disc anomalies (CODA) have optic nerve head excavation that, in some, progressively deteriorates in the absence of elevated IOP. Interestingly, this occurs in a manner similar to that observed in normal tension glaucoma (NTG) patients. Since the only therapy is geared at lowering IOP and these patients have normal IOP, our central hypothesis that genes involved in Mendelian forms of CODA would also be involved in a subset of NTG cases because of the similar clinical phenotypes and provide insight into glaucomatous optic neuropathy. To address this clinically relevant problem, previous work in the laboratory revealed a novel locus on chromosome 12 via linkage analysis and positional cloning of a large autosomal dominant family with CODA; examination of this locus revealed a copy number variation (CNV). Comparative genomic hybridization experiments identified two extra copies of a 6kb segment of DNA that segregates with disease in this family and this copy number variation (CNV) was not detected in unaffected family members or in normal controls. This finding was confirmed by qPCR. Subsequent reporter gene analysis revealed a 774bp transactivating domain within the CNV that drives expression 8-fold higher when subcloned into HEK293T mammalian cells. Moreover, immunohistochemical experiments revealed ubiquitous expression of a matrix metalloprotease gene in retinal sections. We report a CNV within the previously linked region that is co-inherited with CODA in our family. We hypothesize that this CNV leads to dysregulation of gene expression and ultimately to the development of CODA. Ongoing research includes generating animal models.

 

Xitiz Chamlings presentation abstract

The centrosomal protein AZI1 interacts with BBS4 and is involved in ciliary trafficking of BBSome to the cilia

The centrosome is the site of microtubule organization and centriole nucleation, and is essential for cilium formation. Primary cilia, microtubule-based subcellular organelles protruding from the surface of cells, have been shown to be essential for tissue homeostasis, photoreceptor function, olfaction, and several signaling pathways including Hedgehog, Wnt and PDGFR. Defects in cilia or centrosome function lead to phenotypically related syndromes called ciliopathies. Bardet-Biedl syndrome (BBS) is a well-known ciliopathy and most of the BBSome (complex of seven BBS proteins) is known to localize to the centrosome as well as to cilia. In the centrosome, many BBS proteins are thought to interact with centrosomal proteins; for example, BBS4 has been shown to interact with PCM1 and CEP290. Due to the pleiotropic nature of the disease and the abundance of proteins at the centrosome and transition zone where BBS proteins localize, we hypothesized that there are other centrosomal proteins that interact with the BBSome, which have not been identified. Moreover, the functional role of the interaction between BBS and centrosomal proteins has not been fully investigated. Here, we identify a novel BBSome interacting protein, AZI1 (also known as Cep131), which directly interacts with BBS4. We show that AZI1 is involved in ciliary trafficking of the BBSome complex. We also show that AZI1 is required for cilia formation. Under conditions in which the BBSome does not traffic normally to cilia, such as in BBS3 or BBS5 depleted cells, knock down of AZI1 with siRNA restores BBSome trafficking to cilia. Finally, using morpholino knockdown of Azi1 in zebrafish, we were able to show that Azi1 knockdown results in zebrafish phenotypes seen in other Bbs gene knock down, which suggests the possibility that AZI1 might be a new BBS gene.

 

 

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Posted on November 12, 2012, in Student Seminar. Bookmark the permalink. Leave a comment.

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