Evaluating the Role of Senataxin in Class Switch Recombination: A Model for Biological Diversity

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Summary of Research Program The Immunoglobulin (Ig) locus is a fascinating example of a biological system that has evolved multiple strategies to achieve diversity. The evolution of this locus and its regulation can teach us a great deal about how diversity is generated and regulated biologically. Our research program is thus guided by three major questions: 1) What factors have evolved in metazoans to serve specialized roles in regulating Ig diversity? 2) What is the basis for the unique diversification strategies of Ig genes observed across species? 3) How is Ig diversity regulated at the somatic level? In the long term, these studies will provide important new evolutionary insight into how diversity is achieved and regulated at the Ig locus and the consequences of this diversity on multi-organism relationships (symbiotic vs. commensal vs. pathogenic/parasitic). Summary of Proposal Class switch recombination (CSR) is the process used by B cells to generate antibodies of various isotypes. Antibody class (or isotype) is determined by the heavy chain constant region (CH). CSR is mediated by a process of recombination that leads to intrachromosomal deletion. The recombination event occurs between switch (S) regions located upstream of each CH locus, and requires multiple rounds of cellular division. This process is coordinated by a complex set of enzymes including: activation-induced cytidine deaminase (AID), and proteins involved in the DNA damage response. Transcription of S regions is required for CSR and results in the formation RNA-DNA hybrids (R-loops). Senataxin (SETX) is an RNA-DNA helicase that has been shown to promote the resolution of R-loops. It also plays an important role in the DNA damage response. We have recently demonstrated that SETX plays an essential role in regulating the innate immune response to viral infection. Preliminary studies have also suggested that SETX-deficient mice undergo defective CSR in response to vaccination/infection. Using the SETX-/- mouse model we will characterize the role played by SETX during CSR in order to gain a deeper understanding of how the processes of transcription, DNA replication and recombination are concurrently regulated at the immunoglobulin locus. Hypothesis We hypothesize that SETX plays an important role in regulating CSR and that SETX deficiency will impair class switching. Significance These studies will provide important new evolutionary insight regarding how the Ig locus has taken advantage of general cellular factors to perform specific functions that are critical for the generation and regulation of diversity. In the long term, understanding the basic mechanisms governing the generation and regulation of diversity is likely to have broad applications in bioengineering and synthetic biology, wherein creation and regulation of biological diversity is of considerable importance.