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Transcriptional Genomics and Genetics of Van Buchem Disease

Gabriela G. Loots, PhD

Lawrence Livermore National Laboratory.

 

Mutations in distant regulatory elements can negatively impact human development and health,
 yet due to the difficulty of detecting these critical sequences we predominantly focus on coding 
sequences for diagnostic purposes.  Using comparative genomics and transgenesis we are sieving through
 the human genome to identify and characterize tissue-specific enhancer elements.  In particular 
we are focused on regulatory elements that drive expression during skeletal development.  As an example
 of the biomedical applications of our work, I will illustrate how we used comparative sequence-based 
approaches to characterize a large noncoding region deleted in patients affected by Van Buchem disease (VB),
 a severe sclerosing bone dysplasia.  Using BAC recombination and transgenesis we characterized 
the expression of human sclerostin (sost) from normal (hSOSTwt) or Van Buchem (hSOSTvbD) alleles.  
Only the hSOSTwt allele faithfully expressed high levels of human sost in the adult bone and impacted
 bone metabolism, consistent with the model that the VB noncoding deletion removes a sost-specific 
regulatory element.  By exploiting cross-species sequence comparisons with in vitro and in vivo enhancer 
assays we were able to identify an enhancer element that drives human SOST expression in osteoblasts 
and osteocytes, in vivo, and discover a novel function for Mef2 transcription factors during SOST regulation. 
Our approach represents a framework for characterizing distant regulatory elements associated with 
abnormal human phenotypes.