1022-7954/05/4112- © 2005 Pleiades Publishing, Inc. 1425 Russian Journal of Genetics, Vol. 41, No. 12, 2005, pp. 1425–1427. Translated from Genetika, Vol. 41, No. 12, 2005, pp. 1714–1717. Original Russian Text Copyright © 2005 by Potapov, Chekunova, Shustrova, Lavrenchenko, Safronova. The mouse t complex consists of four nonoverlap- ping inversions with a total length about 20 cM occupy- ing the proximal third of chromosome 17 [1]. One of unique properties of t haplotypes is the preferential transmission of t-carrying chromosomes to the off- spring of heterozygous males. This accounts for their relatively wide distribution in the natural populations of the house mouse semispecies Mus domesticus, M. mus- culus, M. castaneus, and M. molossinus [2–5]. The structural organization of the t complex decreases the rate of recombination between the t-carrying chromo- some and its “wild-type” homolog in the given region by a factor of almost 200 compared to the normal value observed under natural conditions [6]. Recombination may occur mainly due to the repetitive nucleotide sequences contained in the t complex; most recombina- tions are nonequilibrium [6, 7]. Moderate repeats (10–30 copies) of the D17Leh66 sequence are of special interest in terms of both the ori- gin and evolution of the t complex and the evolution of the genus Mus and the family Muridae as a whole. This family of cross-hybridizing DNA elements is specific in that they are arranged in two clusters located 3 cM apart [8] in the “wild-type” chromosome of most spe- cies of mice, including M. domesticus, M. musculus, M. castaneus, M. molossinus [2–4], M. abbotti, and M. hortulanus [5]. In contrast, D17Leh66 elements are arranged in tandems in t-carrying chromosomes of these species, as well as M. spretus and the taxonomi- cally remote M. cervicolor and M. caroli [4]. Further studies on the distribution of t repeats in representatives of Muridae are of special interest for revising the taxo- nomic positions of some species from this family and determining the possible ways of its evolution. We used laboratory stocks of mice based on M. domesticus that carried t haplotypes, a “wild-type” chromosome 17, and the marker dominant mutation T (Brachyury) in different combinations, including geno- types +/t w5 , T/t w73 , and T/+, from the collection of the vivarium of the Laboratory of Microevolution (Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences). We also used M. musculus wag- neri (the Caspian Sea coast), Rattus norvegicus, and Phodopus campbelli (the vivarium of the Severtsov Insti- tute of Ecology and Evolution, Russian Academy of Sci- ences), and Lophuromys flavopunctatus (Ethiopia). DNA was isolated from frozen biological material (liver). The liver was homogenized in a buffer solution containing 50 mM Tris-HCl (pH 8.0), 20 mM EDTA, 1% SDS, 0.5 M NaCl, and 1% 2-β-mercaptoethanol; 10 μg/ml proteinase K was added, and the mixture was incubated at 42°C for 16 h. DNA was isolated by the standard phenol–chloroform method [9]. A sample of DNA (10 μg) of each animal was digested with TaqI restriction endonuclease in the corresponding buffer solution. The electrophoretic fractionation of the result- ant DNA fragments was performed in 0.8% agarose gel for 17 h at 45 V. Southern blot hybridization [10] was performed with the use of BA85 nitrocellulose mem- branes (Schleicher & Schull). Plasmids pBR322 con- taining the t-specific DNA sequence Tu66 (obtained by microdissection of metaphase chromosome 17) [11] was used as a blot-hybridization probe. Radioactive labeling of the probe was performed by the nick-translation method until a specific activity of 4 × 10 8 cpm/μg DNA. The hybridization solution con- tained 4× SSC, 1% SDS, 10× Denhardt’s solution, and 500 μg/ml salmon sperm DNA. After the end of hybrid- ization, the membranes were washed three times at 65°C for 15 min in a solution containing 2× SSC and 0.1% SDS and one time in a solution containing 1× SSC and 0.1× SDS. Autoradiography was performed at –70°C for seven days. As evident from the figure, all laboratory mice used as the control group exhibited a characteristic hybrid- ization pattern (lanes 3–5). Unfortunately, some slight t-Specific D17Leh66 DNA Elements in the Family Muridae S. G. Potapov 1 , A. I. Chekunova 2 , I. V. Shustrova 1 , L. A. Lavrenchenko 1 , and L. D. Safronova 1 1 Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, 119071 Russia; e-mail: safronova@sevin.ru 2 Kol’tsov Institute of Developmental Biology, Russian Academy of Sciences, Moscow, 119991 Russia; e-mail: idb@proxima.idb.ac Received April 21, 2005 Abstract—Blot-hybridization analysis with the use of the t-specific probe D17Leh66 has been used to study DNA of various representatives of family Muridae. Hamsters from genus Phodopus have no homologs of this probe, whereas African rats from genus Lophuromys have some homologous elements. This indicates that sequence D17Leh66 is ancient and was probably present in the common ancestor of family Muridae. SHORT COMMUNICATIONS