DNA Repair 12 (2013) 46–52 Contents lists available at SciVerse ScienceDirect DNA Repair j ourna l ho me pag e: www.elsevier.com/locate/dnarepair Tissue-specific mismatch repair protein expression: MSH3 is higher than MSH6 in multiple mouse tissues Stéphanie Tomé a , Jodie P. Simard a , Meghan M. Slean a,b , Ian Holt c,d , Glenn E. Morris c,d , Kamila Wojciechowicz e , Hein te Riele e , Christopher E. Pearson a,b,∗ a Genetics and Genome Biology, The Hospital for Sick Children, TMDT Building 101 College St., 15th Floor, Room 15-312 East Tower, Toronto, ON, M5G 1L7, Canada b Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada c Wolfson Centre for Inherited Neuromuscular Disease, RJAH Orthopaedic Hospital, Oswestry, Shropshire, SY10 7AG, UK d Institute for Science and Technology in Medicine, Keele University, Keele, Staffordshire, ST5 5BG, UK e The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Division of Biological Stress Response, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands a r t i c l e i n f o Article history: Received 20 June 2012 Received in revised form 11 October 2012 Accepted 17 October 2012 Available online 24 November 2012 Keywords: DNA mismatch repair Tissue-specific protein expression Trinucleotide repeats Huntinton’s disease Myotonic dystrophy CAG/CTG repeat instability MSH2, MSH3, MSH6 expression DNA repair genes/proteins a b s t r a c t Mismatch repair (MMR) proteins have critical roles in the maintenance of genomic stability, both class- switch recombination and somatic hypermutation of immunoglobulin genes and disease-associated trinucleotide repeat expansions. In the genetic absence of MMR, certain tissues are predisposed to mutations and cancer. MMR proteins are involved in various functions including protection from replication-associated and non-mitotic mutations, as well as driving programmed and deleterious muta- tions, including disease-causing trinucleotide repeat expansions. Here we have assessed the levels of MSH2, MSH3, and MSH6 expression in a large number of murine tissues by transcript analysis and simul- taneous Western blotting. We observed that MMR expression patterns varied widely between 14 different tissue types, but did not vary with age (13–84 weeks). MMR protein expression is highest in testis, thy- mus and spleen and lowest in pancreas, quadriceps and heart, with intermediate levels in liver, kidney, intestine, colon, cortex, striatum and cerebellum. By equalizing antibody signal intensity to represent levels found in mMutS and mMutS purified proteins, we observed that mMSH3 protein levels are greater than mMSH6 levels in the multiple tissues analyzed, with more MSH6 in proliferating tissues. In the intestinal epithelium MSH3 and MSH6 are more highly expressed in the proliferative undifferentiated cells of the crypts than in the differentiated villi cells, as reported for MSH2. This finding correlates with the higher level of MMR expression in highly proliferative mouse tissues such as the spleen and thymus. The relative MMR protein expression levels may explain the functional and tissue-specific reliance upon the roles of each MMR protein. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. 1. Introduction Mismatch repair (MMR) proteins typically function to maintain genome integrity by removing incorrect or mispaired nucleotides that arise during DNA replication or DNA damage. Eukaryotes have two heterodimeric protein complexes to recognize mismatched DNA: MutS (MSH2-MSH6), which is the major mismatch recog- nition complex and MutS (MSH2-MSH3) [1,2]. MSH2-MSH6 is required to repair base-base mismatches, while MSH2-MSH6 and MSH2-MSH3 are functionally redundant in repair of small inser- tion/deletion loops (1–12 nucleotides). Although MSH2-MSH3 can repair certain base-base mismatches it is preferentially involved in the repair of short CAG or CTG slip-outs [3–6]. Mutations in MMR ∗ Corresponding author at: TMDT Building, 101 College Street, 15th Floor, East Tower, Toronto, Ontario, M5G 1L7, Canada. Tel.: +1 416 813 8256; fax: +1 416 813 4931. E-mail address: cepearson.sickkids@gmail.com (C.E. Pearson). genes (MSH2, MSH6, MLH1 and PMS2) are responsible for a muta- tor phenotype and germ line mutations in these genes underlie hereditary non-polyposis colorectal carcinoma (HNPCC/Lynch syn- drome). MMR can also be pro-mutagenic: MSH2-MSH6 is involved in driving both class-switch recombination and somatic hypermu- tation (SHM) of immunoglobulin genes, programmed mutations for proper immunoglobulin production [7]; MSH2-MSH3 is required to mediate trinucleotide repeat expansions, locus-specific muta- tions that lead to neurodegenerative and neuromuscular diseases including Huntington’s disease and myotonic dystrophy [5,8]. The tissue-specific expression of DNA repair genes may correlate with susceptibility to mutations, genomic instability or tumorigen- esis occurring in certain tissues or cells. For example, expression of the highly mutagenic activation-induced cytidine deaminase (AID) occurs during B cell maturation, which coincides with its role in somatic hypermutation [7]. Other DNA repair proteins including the mismatch repair proteins MSH2 and MLH1 are overexpressed in pre-B germinal center cells, many of which are involved in SHM [9,10]. Thus, in a tissue-specific manner, repair proteins seem to flip 1568-7864/$ – see front matter Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.dnarep.2012.10.006