NIH VideoCast - Concentrating the fury of somatic hypermutation to immunoglobulin genes

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Concentrating the fury of somatic hypermutation to immunoglobulin genes

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Air date:	Wednesday, December 16, 2009, 4:15:00 PM Time displayed is Eastern Time, Washington DC Local
Views:	Total views: 148 * This only includes stats from October 2011 and forward.
Category:	Immunology
Runtime:	00:48:59
Closed captioning:	Check box to display CC outside of the video Note: You can drag the captioning window around and resize it
Description:	Dr. Patricia Gearhart received her Ph.D. in immunology from the University of Pennsylvania in 1974. She performed postdoctoral training at the Johns Hopkins University and was a staff associate at the Carnegie Institution of Washington until 1982. She then became a faculty member, and part of the Immunology Training Program, at the Johns Hopkins University until 1995, when, to the great fortune of the NIH, she moved to the National Institute on Aging. One of the most enigmatic questions in immunology is how the activation-induced deaminase (AID) protein is directed to a very small region of DNA in the immunoglobulin loci, where it causes mutation at a frequency that is a million times greater than in other genes. The purpose of this mutagenic fury is to generate high affinity antibodies and different heavy chain classes. Pat’s lab has used biochemical and genetic techniques to study this fascinating process that is initiated when the activation-induced cytidine deaminase (AID) protein deaminates cytosine in DNA to uracil. First, she and her colleagues demonstrated that uracil is present in the DNA of bacterial cells that express the AID protein. Using quantitative Southern and ligation-mediated PCR techniques, uracils were detected in actively transcribed genes. The uracils were made predominantly on the nontranscribed strand, in accord with the notion that AID acts on single-stranded DNA. Second, they have studied the spectra of mutations in mice lacking mismatch repair proteins and low-fidelity DNA polymerases. Mice deficient for the Msh2-Msh6 heterodimer and DNA polymerase eta have fewer mutations of A:T base pairs, whereas mutations of C:G base pairs can be directly caused by replication or repair of the uracils. Third, using biochemical techniques Pat has demonstrated that the uracil base is recognized by Msh2-Msh6, which then recruits DNA polymerase eta and stimulates its catalytic activity. Thus, synthesis of DNA by this error-prone polymerase can generate mutations downstream of the uracils, including mutations at A:T base pairs. Finally, a major question in antibody diversity concerns how hypemutation is targeted to the immunoglobulin loci, and is not found elsewhere in DNA from B cells. Mutations are localized to two distinct regions: two kilobases of DNA surrounding and including the rearranged variable gene, and four kilobases of DNA encompassing the switch regions. These regions are downstream of promoters, suggesting that transcription is involved in bringing AID to the locus. To address this question, Pat's lab is studying how transcription factors interact with the various enzymes involved in the hypermutation pathway. Understanding this process impacts not only immunology but also cancer biology as it is clear that mis-directed hypermutation can cause lymphomas. Through Pat's work it soon may be possible to assemble all the pieces of the enigmatic hypermutation puzzle. Pat is a keen scientist and exciting speaker. Come catch her enthusiasm for immunology! http://www.grc.nia.nih.gov/branches/lmg/pgearhart.htm The Immunology Interest Group

NLM Title:	Concentrating the fury of somatic hypermutation to immunoglobulin genes / Pat Gearhart.
Author:	Gearhart, P J. National Institutes of Health (U.S.). Immunology Interest Group.
Publisher:
Abstract:	(CIT): Dr. Patricia Gearhart received her Ph.D. in immunology from the University of Pennsylvania in 1974. She performed postdoctoral training at the Johns Hopkins University and was a staff associate at the Carnegie Institution of Washington until 1982. She then became a faculty member, and part of the Immunology Training Program, at the Johns Hopkins University until 1995, when, to the great fortune of the NIH, she moved to the National Institute on Aging. One of the most enigmatic questions in immunology is how the activation-induced deaminase (AID) protein is directed to a very small region of DNA in the immunoglobulin loci, where it causes mutation at a frequency that is a million times greater than in other genes. The purpose of this mutagenic fury is to generate high affinity antibodies and different heavy chain classes. Pat"s lab has used biochemical and genetic techniques to study this fascinating process that is initiated when the activation-induced cytidine deaminase (AID) protein deaminates cytosine in DNA to uracil. First, she and her colleagues demonstrated that uracil is present in the DNA of bacterial cells that express the AID protein. Using quantitative Southern and ligation-mediated PCR techniques, uracils were detected in actively transcribed genes. The uracils were made predominantly on the nontranscribed strand, in accord with the notion that AID acts on single-stranded DNA. Second, they have studied the spectra of mutations in mice lacking mismatch repair proteins and low-fidelity DNA polymerases. Mice deficient for the Msh2-Msh6 heterodimer and DNA polymerase eta have fewer mutations of A:T base pairs, whereas mutations of C:G base pairs can be directly caused by replication or repair of the uracils. Third, using biochemical techniques Pat has demonstrated that the uracil base is recognized by Msh2-Msh6, which then recruits DNA polymerase eta and stimulates its catalytic activity. Thus, synthesis of DNA by this error-prone polymerase can generate mutations downstream of the uracils, including mutations at A:T base pairs. Finally, a major question in antibody diversity concerns how hypemutation is targeted to the immunoglobulin loci, and is not found elsewhere in DNA from B cells. Mutations are localized to two distinct regions: two kilobases of DNA surrounding and including the rearranged variable gene, and four kilobases of DNA encompassing the switch regions. These regions are downstream of promoters, suggesting that transcription is involved in bringing AID to the locus. To address this question, Pat's lab is studying how transcription factors interact with the various enzymes involved in the hypermutation pathway. Understanding this process impacts not only immunology but also cancer biology as it is clear that mis-directed hypermutation can cause lymphomas. Through Pat's work it soon may be possible to assemble all the pieces of the enigmatic hypermutation puzzle. Pat is a keen scientist and exciting speaker. Come catch her enthusiasm for immunology! http://www.grc.nia.nih.gov/branches/lmg/pgearhart.htm The Immunology Interest Group.
Subjects:	Somatic Hypermutation, Immunoglobulin
Publication Types:	Lecture Webcast
NLM Classification:	QU 475
NLM ID:	101522202
CIT Live ID:	8328
Permanent link:	https://videocast.nih.gov/watch=8328

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