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Inverted Repeat Structure of the Sry Locus in Mice

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Inverted Repeat Structure of the Sry Locus in Mice Proc. Natl. Acad. Sci. USA Vol. 89, pp. 7953-7957, September 1992 Genetics Inverted repeat structure of the Sry locus in mice (testis determination/Tdy-1/deletion/Y chromosome) JOHN GUBBAY*, NIGEL VIVIAN*, ANDROULLA ECONOMOU*, DAVID JACKSONt, PETER GOODFELLOWt, AND ROBIN LOVELL-BADGE*t *Laboratory of Eukaryotic Molecular Genetics, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom; and tHuman Molecular Genetics Laboratory, Imperial Cancer Research Fund, Lincoln's Inn Fields, London WC2A 3PX, United Kingdom Communicated by Mary F. Lyon, April 20, 1992 (receivedfor review February 12, 1992) ABSTRACT The testis-determining gene Siy is located on Toward understanding the Sry genomic organization as the short arm of the mouse Y chromosome in a region known well as the regulation of its transcription unit, we have to have undergone duplications and rearrangements in com- compared this genomic region among normal, variant, and parison with the equivalent portion of the human Y chromo- mutant mouse strains. We have analyzed approximately 30 some. Detailed analysis of the Sry genomic locus reveals a kb surrounding Sry in M. musculus musculus and M. mus- further difference in that the mouse Sry open reading frame lies culus domesticus and determined the extent ofthe deletion in within 2.8 kilobases of unique sequence at the center of a large Tdym' XY females. This analysis includes the complete DNA inverted repeat. This repeat, which is found in both Mus sequence ofthe 14.5-kb fragment that must contain the entire musculus musculus and Mus musculs domesticus Y chromo- Sry gene,§ and it reveals a number offeatures about the locus somes, is not present at the human SRY locus. Recombination that allow us to speculate on the mechanism of the deletion. involving the repeat region may have led to an lI-kilobase deletion, precisely excising Sry in a line of XY female mice. MATERIALS AND METHODS Mice. For simplicity, the Y chromosome carrying the There is now abundant evidence that Sry (SRYin humans) is Tdyml mutation is referred to as * in the text. It is of 129 the testis-determining gene on the mammalian Y chromo- strain origin, and therefore ofM. musculus musculus type. It some (1, 2). The gene has many properties consistent with is maintained by breeding XX*f females as described previ- being a switch gene responsible for initiating the male path- ously (13). These mice and normal 129 strain animals were way. For example, it encodes a DNA-binding protein (3, 4) from the colony at the National Institute for Medical Re- and is expressed for a brief period just prior to overt testis search. Animals carrying the Mus musculus poschiavinus Y differentiation (5). Conclusive proof that it is the only chromosome were obtained from stocks maintained by Paul Y-linked gene required for testis determination, and that it is Burgoyne at the Medical Research Council Mammalian De- equivalent to the classically defined locus Tdy (TDF in velopment Unit, London. humans), has come from the demonstration that chromosom- Southern Blotting. DNA samples were electrophoresed on ally female mice transgenic for a 14.5-kilobase (kb) Sry 0.7% agarose gels in 0.09 M Tris borate, pH 8.3/2 mM EDTA genomic DNA fragment can show normal male development (TBE) and transferred onto Hybond-N filters (Amersham) in (6). This experiment also revealed that all the sequences 0.5 M NaOH/1.5 M NaCl. Probes were labeled with necessary for Sry expression are present within this 14.5-kb [32P]dCTP by using a multiprime kit (Amersham), added to region. the filter in 3X SSC/0.1% sodium pyrophosphate/5x Den- Mutations are invaluable in the analysis gene structure hardt's solution/0.1% SDS/10% dextran sulfate containing of denatured herring testis DNA at 50 ,ug/ml and hybridized for and function. Human XY females have been found who 16 hr at 650C (lx SSC = 0.15 M NaCl/0.015 M sodium possess point mutations in the SRY open reading frame, citrate, pH 7.0; lx Denhardt's solution = 0.02% bovine proving that a functional SRY is necessary for testis deter- serum albumin/0.02% Ficoll/0.02% polyvinylpyrrolidone). mination (7, 8) and indicating regions ofthe protein important Filters were washed in 1x SSC/0.1% SDS at 650C for 1 hr and for recognition of target DNA sequences (3, 4). However, then exposed to x-ray film for 1-3 days. there are only a few cases where XY females have been Genomic Library Construction and Screening. DNA from reported in the mouse. In one set of cases, specific Y the appropriate mouse strain was partially digested with the chromosome variants from Mus musculus domesticus sub- restriction enzyme Sau3a and, following methods previously species fail to interact correctly with autosomal loci provided described (2), DNA in the size range 18-23 kb was obtained by the C57BL/6 strain, and this leads to high frequencies of by gel purification. The ends ofthis DNA were partially filled XY females and hermaphrodites (9, 10). The Y variants are in by incubating 50 ,.g for 15 min at room temperature in 50 presumed to have an altered Sty gene compared with that of mM NaCl/10 mM Tris HCl, pH 7.5/1 mM dGTP/1 mM dATP Mus musculus musculus, but this could be in any aspect of containing 15 units of the Klenow fragment of DNA poly- structure or regulation (11). The best case of a mutation merase. Then 0.4 pg of this DNA was ligated to a A FixII directly involving Sry is that provided by the Tdyml mutation vector (Stratagene). The reaction products were packaged by present in a line of XY females (12). This arose in an using Gigapack gold packaging extract (Stratagene) accord- experiment designed to obtain insertion of a retroviral vector ing to the manufacturer's instructions. Phage were plated in into Tdy; however, no retroviral sequences could be found 0.7% top agarose containing 10 mM MgSO4 after adsorption associated with the mutation. Instead, initial findings dem- to plating bacteria for 15 min at 370C (ref. 14, p. 63). Plating onstrated that at least part of the Sry open reading frame had bacteria were prepared by resuspending an overnight culture been deleted (2). of strain DL652 in ice-cold 10 mM MgSO4. Phage DNA was The publication costs of this article were defrayed in part by page charge tTo whom reprint requests should be addressed. payment. This article must therefore be hereby marked "advertisement" §The sequence reported in this paper has been deposited in the in accordance with 18 U.S.C. §1734 solely to indicate this fact. GenBank data base (accession no. X67204). 7953 Downloaded by guest on September 26, 2021 7954 Genetics: Gubbay et al. Proc. Nati. Acad. Sci. USA 89 (1992) p2.3/A p2.3/A transferred to Hybond-N filters, denatured in 0.5 M NaOH/ f f 1.5 M NaCi, neutralized in 1 M ammonium acetate, and L741 hybridized as described in Southern Blotting. Sequencing. The dideoxy method of sequencing (15), using the T7 sequencing kit (Pharmacia), was performed according L823 to the manufacturer's instructions. Sequence analysis was performed by using software designed by the Genetics Com- puter Group at the University of Wisconsin (16). Polymerase Chain Reaction (PCR). For PCR analysis 0.1 jug 9.0 2.3 0.2 2.8 3.5 1.5 2.8 0.2 2.3 9.0 I Locus of genomic DNA was 'added to a 50-,IA reaction mix contain- I 0 ing 50 mM Tris*HCl at pH 9.0, 15 mM ammonium sulfate, 7 Li 041 mM MgCl2, bovine serum albumin at 0.17 mg/ml, 0.05% 0.4 Nonidet P-40, 3.75 mM each dATP/dCTP/dGTP/dTTP, 1 unit of Thermus aquaticus (Taq) DNA polymerase (Anglian), L951 and between 250 ng and 1 gg of each primer. Amplification L952 consisted of denaturation for 3 min at 940C followed by 30 L961 cycles of 960C for 40 s, 650C for 70 s, and 720C for 100 s in a Hybaid thermal reactor model HBTR1. PCRs were carried FiG. 1. Guide to Sry genomic clones and structure of the wild- out in duplicate on each sample: (i) with 1 jg of a single type and X* female locus. EcoRI restriction maps of the following primer (5'-GTGTCTCAAAGCCTGCTCTTC-3') designed to genomic phage inserts are shown: L741, L832, and L823, Sry locus amplify a 522-base-pair (bp) fragment across the deleted from a 129 mouse (M. musculus musculus Y chromosome); L951, region in L952, and L961, Sry locus from an M. musculus poschiavinus mouse genomic DNA from X1 female mice; (ii) with 500 (M. musculus domesticus Y chromosome); and L1041, Sry locus ng each of primers for the Sry box region (5'-GAGAGCATG- from an X* female mouse carrying the Tdym" mutation (the broken GAGGGCCAT-3' and 5'-CCACTCCTCTGTGACACT-3') line indicates deleted sequences). The Sry open reading frame is in and 250 ng each of primers for Zfy-1 (5'-GACTAGACAT- the 5'-to-3' orientation from left to right. The orientation ofthis clone GTCTTAACATCTGTCC-3' and 5'-CCTATTGCATGGAC- with respect to the Sry box is not known. Restriction sites are TGCAGCTTATG-3') (6). For visualization an 8-4 aliquot indicated by vertical dashes. The position ofthe Sry box is indicated was electrophoresed on a 2% agarose/TBE gel containing by a shaded box. The positions ofprobe p2.3/A are shown by arrows. ethidium bromide at 0.1 ,ug/ml. XY d Locus indicates the derived restriction map of the wild-type locus.
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