Allison Cox and Hannah Seberg to present at Student Seminar 7/26/2016
Genes involved in bone remodeling are mutated in chronic recurrent multifocal osteomyelitis (CRMO)
Chronic recurrent multifocal osteomyelitis (CRMO) is a rare, pediatric, autoinflammatory disease characterized by bone pain due to sterile osteomyelitis, and is often accompanied by psoriasis or inflammatory bowel disease. Via whole-exome sequencing, we detected a homozygous mutation in the filamin-binding domain of FBLIM1 in an affected child with consanguineous parents. Microarray analysis of bone marrow macrophages from the CRMO murine model determined that the Fblim1 ortholog is the most differentially expressed gene, further implicating it in disease pathogenesis. We sequenced FBLIM1 in 96 CRMO subjects and found a second proband with a novel frameshift mutation in exon 6 and a rare regulatory variant. In two other families, we detected a shared rare mutation in a related gene, PLCG2. FBLIM1 and PLCG2 are both directly involved in β-integrin activation, which was recently implicated in sterile inflammation via Bruton tyrosine kinase signaling. Additional work involves functional validation of the FBLIM1 and PLCG2 mutations, and pathway analysis of exomes from a cohort of individuals with CRMO. Our data suggest CRMO is a disorder of integrin activation and imbalanced bone remodeling.
TFAP2A drives melanocyte gene expression in parallel with MITF
Hannah E. Seberg, Eric Van Otterloo, Stacie K. Loftus, Greg Bonde, Ramakrishna Sompallae, Juan F. Santana, J. Robert Manak, William J. Pavan, Robert A. Cornell
Disruption of the transcription factor network governing melanocyte differentiation contributes to the pathogenesis of pigmentation disorders and melanoma. Transcription factor activator protein 2 alpha (TFAP2A) is expressed in melanoblasts, and mutations in this gene cause pigmentation phenotypes in humans, mice, and zebrafish. However, the the transcriptional targets of TFAP2A, and the extent to which they are shared with MITF, a master regulator of melanocyte biology and melanoma progression, have been unclear. To determine the position of TFAP2A in the melanocyte gene regulatory network, we conducted anti-TFAP2A ChIP-seq to create profiles of TFAP2A-bound loci in melan-a cells and human primary melanocytes. We then used microarray analysis in zebrafish and mouse immortalized melanocytes (melan-a cells) to profile genes that are downregulated in the absence of TFAP2A. Genes at the intersection of the microarray and ChIP-seq profiles are likely direct targets of TFAP2A. These include mc1r and several melanin synthesis or melanosome structural genes, most of which are also thought to be direct targets of MITF. Comparison of our TFAP2A ChIP-seq profile with a published MITF ChIP-seq profile showed that TFAP2A peaks overlap MITF peaks at a large fraction of promoters and enhancers. In reporter assays, deletion of TFAP2A binding sites decreased activity of a minimal TRPM1 promoter, similar to published results for deletion of MITF binding sites from this element. We also observed a genetic interaction between tfap2a and mitfa in zebrafish. The significance of these findings is, first, they show that TFAP2A and MITF work in parallel to promote gene expression in melanocytes. Second, they show that a widely-expressed transcription factor, TFAP2A, co-operates with a more tissue-restricted transcription factor, MITF, to directly regulate expression of lineage-specific melanocyte genes. Third, they suggest that the reduction of TFAP2A expression levels observed in advanced melanoma is a cause and not an effect of melanoma progression, as such a reduction would be expected to decrease the pro-differentiation effect mediated by TFAP2A.