home > faculty > schatz

DAVID SCHATZ

The B and T lymphocytes that constitute the adaptive immune system make use of an extraordinarily diverse array of antigen receptor molecules (immunoglobulins and T cell receptors) to combat viral and bacterial infections.  The Schatz lab is interested in understanding the two major processes that generate this diversity:  V(D)J recombination and somatic hypermutation.

V(D)J Recombination

V(D)J recombination assembles immunoglobulin and T cell receptor genes from component V (variable), D (diversity), and J (joining) gene segments.  In the first phase of the reaction, two DNA segments are bound by the recombination machinery, brought into close physical proximity, and the DNA is cleaved.  In the second phase, the DNA ends are processed and joined by the cellular DNA repair machinery to form the reaction products.  One major interest of the lab is the enzymatic mechanism of the first phase, which is catalyzed by the proteins encoded by the recombination activating genes, RAG1 and RAG2.  We are studying how the RAG proteins bend and twist the substrate DNA in order to execute DNA cleavage and have developed fluorescence resonence energy transfer (FRET) as a method to study the structure of protein-DNA complexes formed by the RAG proteins.  We are currently using FRET to characterize the conformational changes that accompany DNA binding by RAG1/RAG2 and X-ray crystallography to study RAG-DNA interactions.

Recently, we have used chromatin immunoprecipitation (ChIP) to demonstrate that the RAG proteins associate with one small, focal region of each antigen receptor locus.  We propose that these "recombination centers" are specialized sites within which the two recombining gene segments are brought together.  Interestingly, each RAG protein has the ability to be recruited into recombination centers in the absence of the other, suggesting several distinct levels of regulation of RAG binding.

Somatic Hypermutation

Somatic hypermutation introduces point mutations into the variable regions of immunoglobulin genes (which encode antibodies) in B cells during an immune response.  These mutations allow for the generation of B cells expressing antibodies with high affinity for an invading microorganism, which helps protect individuals from recurrent infections with the same microorganism, and underlies the success of many vaccines.

Somatic hypermutation is initiated by activation induced deaminase (AID), which deaminates cytosine to create uracil in immunoglobulin genes. The uracil is then processed by DNA repair pathways to create mutations.  We have demonstrated that mutations can spread approximately 30 base pairs in both directions from the site of deamination and that this spreading process occurs in a strand asymmetric manner.  A major interest of the lab is to understand how somatic hypermutation is targeted to immunoglobulin loci.  Recently, we have discovered that the genome is protected from damage due to somatic hypermutation by two distinct mechanisms:  specific targeting of AID and gene-specific high-fidelity DNA repair.  Surprisingly, a large number of non-immunoglobulin genes are hit by AID but fail to accumulate  mutations because of high-fidelity DNA repair.  These genes include many, such as Myc, that have been implicated in the development of B cells malignancies.  An important implication is that anything that undermines high-fidelity repair would be expected to allow for widespread accumulation of mutations, with potentially disastrous consequences.

Selected Publications

Yang, S. Y., Fugmann, S. D. and Schatz, D. G. Control of gene conversion and somatic hypermutation by immunoglobulin promoter and enhancer sequences.  J. Exp. Med. 203, 2919-2928 (2006)

Drejer-Teel, A. H., Fugmann, S. D. and Schatz, D. G. The beyond 12/23 restriction is imposed at the nicking and pairing steps of DNA cleavage during V(D)J recombination.  Mol. Cell. Biol. 27, 6288-6299 (2007)

Ciubotaru, M., Kriatchko, A. N., Swanson, P. C., Bright, F. V. and Schatz, D. G. Fluorescence resonance energy transfer analysis of recombination signal sequence configuration in the RAG1/2 synaptic complex.  Mol. Cell Biol. 27, 4745-4758 (2007)

Unniraman, S. and Schatz, D. G. Strand-biased spreading of mutations during somatic hypermutation.  Science 317, 1227-1230 (2007)

Liu, M., Duke, J. L., Richter, D. J., Vinuesa, C. G., Goodnow, C. C., Kleinstein, S. H. and Schatz, D. G.  Two levels of portection for the B cell genome during somatic hypermutation.  Nature 451, 841-845 (2008)

Last Updated 09-22-08