Comparative Gene Mapping in the DomesticCat (Felis catus)S. J. O'Brien, S. J. Cevario, J. S. Martenson, M. A. Thompson,W. G. Nash, E. Chang, J. A. M. Graves, J. A. Spencer, K.-W. Cho,H. Tsujimoto, and L. A. Lyons

From the Laboratory of Genomlc Diversity, NationalCancer Institute, Frederick Cancer Research and De-velopment Center, Frederick, MD 21702-1201 (O'Brien,Cevario, Martenson, Thompson, and Lyons), H&W Cy-togenetlc Services, Inc., Lovettsvllle, Virginia (Nash),the Lombardl Cancer Center, Georgetown University,Washington, D.C. (Chang), the Department of Geneticsand Human variation. La Trobe University, Bundoora,Victoria, Australia (Graves and Spencer), and the De-partment of Veterinary Internal Medicine, University ofTokyo, Tokyo, Japan (Tsu)lmoto, Cho). This paper wasdelivered at a symposium entitled "Interspedes Hy-brids In Mammals" In association with the New Zea-land Genetical Society and Australasian Gene MappingWorkshop In Dunedln, New Zealand, from November30-December 1, 1995.

Journal of Heredity 1997^8:408-414; 0022-1503/97/15.00

The genetic map of the domestic cat has been developed as a model for studyingboth feline analogues of human genetic disease and comparative genome organi-zation of mammals. We present here the results of syntenic mapping of 35 genesbased upon concordant occurrence of feline gene homologues with feline chro-mosomes and previously mapped loci in a panel of 41 rodent x cat somatic cellhybrids. These somatic cell hybrids retain rodent chromosomes and segregate fe-line chromosomes, but in different combinations in each hybrid cell line. Thirty-three of the 35 new locus assignments extend and reaffirm conserved chromosomesegment homologies between the human and cat genomes previously recognizedby comparative mapping and zoo-FISH. These results demonstrate the extensivesyntenic conservation between the human and feline genomes and extend the fe-line gene map to Include 105 assigned loci.

Genetic mapping of homologous loci in di-verse species reveals that genomic orga-nization is not a random process (Com-parative Genome Organization 1996; Co-peland et al. 1993; DeBry and Seldin 1996;Nadeau et al. 1995; O'Brien et al. 1988).Blocks of linked genes have been shownto be preserved throughout evolution andthese blocks can exist intact in species asdiverse as humans and flies. This conceptis best exemplified by the comparison ofgenomic localizations of homologousgenes that have been mapped in both hu-mans and mice. Approximately 130 chro-mosomal segments are shown to be con-served when homologous genes arealigned in the two species [ComparativeGenome Organization 1996; Copeland etal. 1993; DeBry and Seldin 1996; Nadeau etal. 1995; Mouse Genome Database (MGD)].The conserved segments likely reflect anancestral genomic organization that hasbeen inherited throughout the evolutionof rodents and primates. Similar conclu-sions were reached when comparison ofhuman and cattle gene maps revealed ex-tensive conserved syntenic segments(Barendse et al. 1994; Bishop et al. 1994;Ma et al. 1996; Womack and Kata 1995).

The feline genome has also proven tohave a genomic organization highly con-served relative to human. This conserva-tion has been evident by both compara-tive gene mapping and G-banded cytolog-

ical comparisons (Lyons et aJ. 1994, 1997;Nash and O'Brien 1982, O'Brien and Nash1982; O'Brien et al. 1993, 1997). More re-cently, reciprocal chromosome paintingusing individual probes from flow-sortedhuman and feline metaphase chromo-somes has demonstrated by direct obser-vation the conservation between the fe-line and human genome organizations(O'Brien et al. 1997; Wienberg et al., inpress).

Pathological analogues of over 30 inher-ited human diseases have been describedin the domestic cat (Migaki 1982; Nicholasand Harper 1996; Nicholas et al. 1996). Fe-lines are also an excellent model for infec-tious and acquired diseases, specificallyfeline leukemia virus (Hardy et al. 1980)and feline immunodeficiency virus (Car-penter and O'Brien 1995; Pedersen 1993).Feline leukemia is an extensively studiedmodel for virus-induced cancer, while fe-line immunodeficiency virus induces felineAIDS. Extension of the cat gene map willfacilitate disease gene analyses and the fe-line genome can serve as the carnivorerepresentative for genome evolutionarystudies.

We are continuing to develop the genet-ic map of the cat using both type 1 (codinggene) and type n (microsatellite markers)loci (Menotti-Raymond and O'Brien 1995;O'Brien 1991; O'Brien et al. 1993). In thepresent study, 35 genes are assigned to fe-

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Table 1. Molecular gene c lone* used to track fel ine homologues In Southern blot analyses

Gene symbol

ABUARAF1CD8ACOL1A1CSF1REGFREGR1F9FESFGF1FGF3FOSFYNGUH0XA4HRASHRASPILIAIL8JUNKITKRAS2MOSMYBMYCMYCNNRAS

orePDGFBPIM1ROS1SRCTHRA1WNT1YES1

Clone

pAOglSAraQ81pT8FlHf677

pAEBamRIEGR1pf9pA08gEGG177p39Ap(os-lpFynpKK36plHox 1.4pUC EJ6.6pBR-NTIL-laIL8pHJphcldt-171pSWll-1pABc-mybpHSR-1pNB-1-Subp52CpOTCpPHS-1phplm5R]pROSphu-csrcpHE-AlpMT2.5pXEyes

Vector

pUC19pUC19pSP6pBR322

pBR322pUC13pGEMpAT153pDH15pUC12pBR322pucl9pGem3pBR322pUC13pBR322pBR322pucl9

pUC19pUC13pBR322pUC18pBR322pGem3pUC12pUC9pUC18pytpBR322pUC8pBR322pBR322pUC19

Insert (Kb) R.E.-

1.2&ORII.6&0RI1.7£coRI1.8£coRl

BamHl/EcoW3.1 £coRI1.5tf/ndUI/£coRI2.2 EcoRl0.6 7a<7l0.9 ft/I1.6 tfincIU/fcoRl1.55 ft/10.98 Windlll6.6 BamHI10.7 BamHI1 7 EcoRl/HwdlW0.5, 1.2&ORI0 9ftrt1.25 Ssl\0.6, 0.5 ft/I/£coRI0.6 Aval/BamHl0.5£coRl9.0 EcoRl1.0£coRI/BamHI1.5£coRl1.31.3 BamHl3.6 £coRl0.8 PvM/EcoRl\.7 Hindm/EcoRl3.9 £coRJ2.5 BamHl/firoRI0.55 £coRJ/ftrt

Species oforigin

FelineMouseHumanHuman

AvianMouseHumanFelineHumanMouseMouse

HumanHumanHumanHumanHumanHumanHumanHumanHumanMouseMouseHumanHumanHumanRatFelineHumanAvianHumanHumanMouseHuman

R.E. Mouse/Hamster

Bg/UBg/UBamHlBg/1

BamHIBg/IIPsAKpn\EcoKi/Bgl IIBamHI

ftrl/BamHIBgill/Bamrfl6:oRISad

BamVAEcoNflg/IIftrt/Bg/ISadEcofQBg/II

Bg/DSadft/IBglOSsl\Hindin/HindlUBgiflBamHl/SstiSsfift/I

Reference/Source

Blochlmica et Blophysica Acta 824:104-112, 1985Mol Cell Biol 6:2655-2662, 1986Cell 40:241, 1985ATCC #61322

ATCC #41019Sukhatme (unpublished)Nature 299:178-180, 1982Gene 35:33-43, 1985Science 233:541-545, 1986R. CardiffJ. Virol 44:674, 19??ATCCScience 236.70-73, 1987Genomics 5:250-258, 1989ATCC #41028ATCC #41001DA1NIPPON Pharmaceutical CO:LTDJ Exp Med 167:1883, 1988BohmanATCC #59492ATCC #41027G. Vande WoudePNAS 835010-5014, 1986ATCC #41010ATCC #41011ATCC #41030Eur J Blochem 143:183-187, 1984Gene 3533-43, 1985ATCC #59168B. VogelsteinMol Cell Blol 5:831-338, 1985J Virol 36(2):575-585, 1980Cell 31:99-109, 1982ATCC #57582

• Restriction eiuymes used to release the Insert from the vector.

line chromosomes by Southern blot anal-yses using a panel of somatic cell hybridsbetween rodent and feline cells (O'Brienand Nash 1982). Each hybrid cell line hasbeen karyotyped to identify the retainedfeline chromosomes. Seventy genes havebeen previously mapped using this samehybrid panel. Thirty-three of the new geneassignments could be predicted by previ-ous mapping data that delineated blocksof chromosomal segments that are con-served between felines and humans. Thenew genes increased the genetic map ofthe cat to 105 loci, which encompasses 18of the 19 feline chromosomes (27V = 38),showing 15 multigene blocks of conservedchromosomal segments with humans.

Materials and Methods

Molecular clones and probes for the 35genes are described in Table 1. The iden-tity of each probe was verified by confirm-ing that the expected fragment size fromhuman DNA for each probe was obtainedby a Southern blot analysis. The develop-ment of the hybrid cell lines has been de-scribed (Berman et al. 1986; Gilbert et al.1988; Masuda et al. 1991; O'Brien 1986;

O'Brien and Nash 1982). Hybrid lines werecharacterized by chromosomal G-bandingand isozyme typing, which has been de-scribed (Berman et al. 1986; Gilbert et al.1988; Masuda et al. 1991; Nash and O'Brien1982; O'Brien and Nash 1982). The felinechromosomal constitution of a single pas-sage for each hybrid cell line Is presentedin Table 2. Genotypes for all passages ofevery member of the cell panel are includ-ed in the Web site for the Laboratory ofGenomic Diversity (http://www.nci.nih.gov/intra/lgd/lgdpage.html).

DNA was purified from the parental andthe 42 hybrid cell lines by standard phenoland chloroform extraction methods (Man-iatis et al. 1982). Southern blots of the pa-rental samples were used to determinewhich enzymes would distinguish hybrid-ization patterns that would be diagnosticbetween the cat, the mouse, and the ham-ster. Each sample (10 ng) was digestedwith seven different enzymes—BamHI,Bglll, EcoRl, Hindm, ft/I, Sst\, and Kpn\—using conditions as recommended by themanufacturer (GIBCO BRL). Digested sam-ples were separated by electrophoresis In1.0% agarose gels at 40 V for 18 h. DNAblotting and hybridization were performed

following standard protocols (Modi et al.1987) with the following modifications.Southern blots were hybridized for 40 h at37°C in 50% formamide, 1 M NaCl, 50 mMPIPES (pH 6.8), 200 ng/ml denatured salm-on sperm DNA, 10 mM EDTA, and 10XDenhardt's solution (0.2% Ficoll, 0.2% po-lyvinylpyrrolidone, and 0.2% bovine se-rum albumin). The gene-specific insert foreach probe was isolated from the vectorusing the appropriate restriction enzymes(Table 1). The inserts were separatedfrom the vectors by agarose-gel electro-phoresis and the inserts were isolated byexcision from the gels followed by purifi-cation with GeneClean (Bio 101). Vectorinserts were radiolabeled by randompriming following manufacturer's recom-mendations (Boehringer Mannheim). Thefilters were initially washed in 2x SSC,0.1% SDS for 30 min at 50°C; the final washwas lx SSC for 30 min at 65°C. Washeswere changed every 30 min and washstringencies were increased as requiredfor each probe. Stringency was increasedby increasing temperatures and decreas-ing SSC concentration as required to re-duce background radiation on the filters.Blots were exposed to X-ray diagnostic

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Table 2. Chromosome constitution of cat x rodent somatic cell hybrid panel

Feline chromosomes

Hybrid

17T1G17T2F17T3E17T4E17T5H17T6D17T7D17T8F17T9D17T10C17T11D17T12G17T26D17T27D17T28E17T29D17T30C17T33E17T34D17T35F17T36E17T37D49C1E49C3E49C4B49C5C49C6D49C7D49C9C49C10B49C11C49C12D49C13F49C14F49C15E49C16G49C17A49C18F49C19E49C20D4OC21D49C22E49C23A49C24D49C25A

Al

++10035

+

80+

+

20+

1001005050

+

64+

2090

+

A2

+

65

9

+60

100+

+

+70

+

A3

80

5070

+

80

80

++

100100

Bl

++

25

+

60

10++80104050

++

14

70

40+

B2

++

30

+

++

+

+50

100

60100+

+

B3

++80

90

55060

+18

100+80

100++

100100

+70

+

B4

++80

+

+

+

4070

+

47

82

720

80100+

+

100

Cl

20

+

35

18

5080+

C2

++10050

+

10100

100

+5

+

10035

40

100++

6+100

+7167

100

100100++

100100

Dl

50

3020

+

+100

217

40

80100+

D2

2025

100

40

2015

++

713

+

+

D3

10

5

+

12

55+8633

80100+

D4

10060

+

++50

8070

+

53

18

767

+

4080

+

+50

+

El

30

+

304040

24

E2 E3 Fl

25+

+ +

+

++

60

5++

+ +

730

80

+

F2

++1004060

++

100100

100

+100++1001008070

++

18+100

+79

100

100

+

+

30

X

++

60

6090

10++100

4050

100100

+82

18+8667

100+100100++

100100

+60

+

Y

15

100

100

40

Each cell hybrid was karyoptyped using high-resolution G-trypsIn banding and scored for the presence of everycat chromosome. " + " Indicates ^30% of metaphases had Indicated chromosome. Numbers are actual percentagesof examined metaphase spread that retained the chromosomes In the specific cell hybrid passage 17T series aremouse RAG cell X feline lymphocyte hybrids. 49C series are Chinese hamster E36 X feline lymphocyte hybrids(O'Brien and Nash 1982).

film (Kodak X-OMAT XRP-5) for 2-7 daysand developed using a AFP Imaging Mini/Med 90 X-ray film processor. The purifiedDNA samples from the hybrid lines weredigested with diagnostic enzymes and thedigested products were separated, blot-ted, and hybridized as described above.

Each hybrid line was scored as positivefor a gene if a unique feline hybridizationpattern was seen and negative if no hy-bridization pattern for the cat was detect-ed. If hybridization signals were difficult toscore, the Southern blot was repeated us-ing DNA from a different culture passageof the same hybrid line. Scores werechecked for concordancy and discordancywith all other known markers typed in thehybrid lines including chromosomes, iso-zymes, and other genes (Table 2). Chi-

square values were calculated from a 2 x2 contingency table where marginal fre-quencies were used to estimate expectedvalues. Gene symbols are as determinedby the human nomenclature committee(Fasman et al. 1996; McAlplne et al. 1994).

Results

Thirty-five genes were assigned to chro-mosomes in the feline genome. The geneassignments were made by Southern blotanalyses of heterologous probes on a pan-el of DNA from 45 rodent x feline somaticcell hybrid lines. The assignments werebased upon concordant association ofeach gene hybridization signal with felinechromosomes and markers that were pre-viously mapped in the hybrid panel (Fig-

ure 1). Each gene produced a hybridiza-tion signal specific for the cat that was adifferent molecular size(s) than the signalsproduced by the mouse or the hamster(Figure 1). The chromosome assignment,range of discordant hybrid frequency, plusa chi-square test for gene chromosome as-sociation is presented in Table 3. An av-erage of 32 hybrid lines were scored to cal-culate concordancy and disconcordancyfrequencies.

Gene markers were assigned to chro-mosome based on concordance withG-banded chromosomes, by concordancewith gene markers previously assigned tothat chromosome, and by high discor-dance with other chromosomes and genemarkers. Thus the genes CD8A, ILIA,MYCN, and SRC were assigned to felinechromosome A3 with four supportivemarkers each, and FGF3 was assigned tofeline chromosome Dl with three support-ive markers (Table 3). These four genesalso displayed high discordancy frequen-cies with chromosomes and genes fromthe other feline chromosomes. For exam-ple, CD8A maps to feline chromosome A3concordant with four gene markers (ADA,ACPI, MDH1, and ITPA). The discordancyof CD8A versus chromosome A3 markersranged from 0.0 to 8.0% with the associ-ated chi-square values of 9.3-22.5. A highchi-square value, 11.2, was observed be-tween CD8A and a marker on feline chro-mosome B3, but the discordance washigh, 19%.

MYC, HMBS, and THRA1 had strong con-cordance and chi-square values for mark-ers on feline chromosomes F2, Dl, and A3,respectively. These three genes also had ahigh concordancy value with one markernot located on the designated chromo-some, but other markers from the othersyntenic group were highly discordant.For example, the concordance for THRA1to chromosome A3 and to nine othergenes on chromosome A3 was 87-92%with corresponding chi-square values of6.7-21.4. THRA1 was 88% concordant withthe feline X chromosome with a chi-squareof 11.36, but the only other X marker,G6PD, was 68% discordant with a chi-square of 7.77.

The 35 genes localized to 14 of the 19feline chromosomes (Figure 2). Thirty-onegenes mapped to positions within previ-ously known conserved syntenic seg-ments that occur between the feline andhuman genome. MYC is the first gene tobe mapped to feline chromosome F2.Three feline genes—THRA1, MOS, andPDGFB—were asyntenic with markers that

4 1 0 The Journal erf Heredity 1997:88(5)

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3 1_ —

O O O CD Q Qo n 2 m to r»eo (O rt co co o

Cat -». _

Hamster -». (

INT1

Kb

23.2

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Cat-

HamsterMouse

MYB

Kb

9.46.7

2.32.0

U . U U U O O O 0 Q O O

S S S S S P

Mouse -*.

Cat - •

Kb

. 23.1

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w ID i»• «* to o •

•= § 0 0 0 0 0 0 0 o o | -

Hamster t- 9.4<- 6.7

ARAF1 YES1• • - •

Cat-*.

Mouse - *

FGF3

:at

Mouse

m

7T12F

7T26C

|

7T27C

|m

7T28C

|m

7T29C

|m

7T30D

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7T33D

I

7T34C

1

7T35C

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7T36C

1

7T37D

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1. Kb

1 •« - 6.71 < - 4.4

1 < - 2.3• • - 2.0

Mouse - •

C a t - *

C a t - *

GLI

u o o o m u u0 ) o m v m ( D r

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Hamster -»

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UJ

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UJ

49C3

UJ

49C4

UJ

49C5

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49C7

—

O

49C9 106*

(J

49C1

O

49C1

• •

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£

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sO

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FES

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Hamster —»•Cat -»•Cat - »

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Hamster -»• w «

Cat-*. • •

JUN

Figure 1. Southern blot analyses of 10 genes In the feline and rodent somatic cell hybrid panel. Gene abbreviations follow human nomenclature (McAlpine et al. 1994;Fasman et al. 1996) and are defined In Table 3.

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Table 3. Syntenic assignments of 37 genes in the feline genome

Genesymbol

Chromosome location

Gene name Human Cat

DiscordancyDiscordancy range* No. of range/otherChi-square range* hybrids chromosomes'

ABL1 Abelson murine leukemia viral (v-abl) oncogene homologue 1 9q34.1 D4(iyARAF1 Murine sarcoma 3611 viral (v-raf) oncogene homologue 1 Xpll.3-pll.23 X(2)CD8A CD8 antigen, alpha polypeptlde (p32) 2pl2 A3(4)COL1A1 Collagen, type 1, alpha 1 17q213-q22 El(l)CSFIR Colony stimulating Factor Receptor FMS Oncogene 5q33.2q34 Al(2)EGFR Epidermal growth factor receptor (v-erb-b) 7pl2 A2(2)EGR1 Early growth response 1 5q23-q31 Al(2)F9 Coagulation lactor K Xq26.3^27.1 X(2)FES Feline sarcoma (Synder-Thellen) viral (v-fes)/Fujinaml avian sarcoma (PRCD) 15q26.1 B3<3)

viral (v-fps) oncogene homologueFCF1 FIbroblast growth factor 1 (acidic) 5q313-q33.2 A 1(2)FGF3 FIbroblast growth factor 2, murine mammary tumor Integration site (v-lnt-2) 1 Iq l33 Dl(3)

oncogene homologueFOS FBJ murine osteosarcoma viral (v-fos) oncogene homologue 14q24.3 B3(3)fflV FYN oncogene related to SRC, FGR, YES, SYR 6q21 B2(4)GU Glloma-assoclated oncogene homologue 12ql3 B4(4)H0XA4 HomeoboxA4 7pl5-pl4 A2(l)HRAS Harvey rat sarcoma viral (v-Ha-ras) oncogene homologue Ilpl5.5 Dl(4)HRASP Harvey rat sarcoma viral (v-Ha-ras) oncogene homologue pseudogene Xpl 1.3-pl 1^3 X(2)ILIA lnterleukln 1, alpha 2ql3 A3(4)US lnterleukln 8 4ql3-q21 Bl(2)JUN Avian sarcoma virus 17 (v-Jun) oncogene homologue Ip32-p31 Cl(4)KIT Hardy-Zuckerman 4 feline sarcoma viral (v-klt) oncogene homologue 4ql2 Bl(2)KRAS2 Klrsten rat sarcoma 2 viral homologue (v-KI-ras2) oncogene 12pl2.1 B4(3)MOS Moloney leukemia sarcoma virus (v-mos) oncogene homologue 8qll B2(4)MYB Avian myelobastosls viral (v-myb) oncogene homologue 6q23.3-q24 B2(4)MYC Avian myelocytomatosis viral (v-myc) oncogene homolog 8q24.12-q24.13 F2(l)MYCN Avian myelocytomatosis viral related oncogene 2p24.3 A3(4)NRAS Neuroblastoma Ras viral (v-ras) oncogene homologue Ipl3 Cl(4)OTC Ornlthlne transcarbomoyi-transferase Xp21.1 X(2)PDGFB Platelet-derived growth factor beta polypeptlde (sis oncogene) 22ql2.3-ql3.1 B4(4)PIM1 Plm-1 oncogene 6p21 B2(4)ROS1 Avian UR2 sarcoma virus oncogene (v-ros) homologue 6q21-q22 B2(4)SRC Avian sarcoma (Schmldt-Ruppln A-2) viral (v-src) oncogene homologue 2Oqll.2 A3(4)THRA1 Thyroid hormone receptor, alpha 1 (avian erythroblastlc leukemia viral • 17qll.2-o.12 A3(9)

(v-erb-a) oncogene homologue 1, (ERBA1)WNT1 Murine mammary tumor Integration site (vMnt-1) oncogene homologue 12ql3 B4(4)YES1 Yamaguchl sarcoma viral (v-yes-1) oncogene homologue 18pll.31-pll.22 D3(l)

0.05/25.40.10-0.13/19.8-18.90.00-8.0/22.5-9.30.10/550.00-0.03/29.2-14.20.03-0.10/25.4-16.20.06-0.17/8.5-12.80.03-0.05/30.1-25.80.03/32.4-30.5

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• Discordancy range: Range of measured frequency of hybrids' discordance for tested gene versus Implicated chromosome by G-banded karyology plus test gene vs. othergene markers previously mapped to that chromosome.

kChl square: Test for random occurrence of hybrids In four categories with respect to gene/marker combinations: +/+, + / - , — /+ , and — /—.' Discordancy range: Range of hybrids discordant for gene versus all other cat chromosomes.' In paretheses Is number of gene markers previously mapped to implicated chromosome that were typed for concordance with the mapped gene

are syntenic in humans. THRA1, a gene onhuman chromosome 17, mapped to A3.Two other human chromosome 17 mark-ers—TP53 and COL1A1—mapped to felinechromosome El. Feline chromosome A3now has markers from three different hu-man chromosomes—17, 20, and 2. MOSmapped to feline chromosome B2 in con-trast to the other human chromosome 8markers, GSR and MYC, which are locatedon feline chromosomes C2 and F2, respec-tively. Feline chromosome B2 has an ex-tensive human chromosome 6 gene clus-ter and MOS is the only marker on B2 thatis from a different human chromosome.PDGFB is the only marker on feline chro-mosome B4 that is not from human chro-mosome 12. YES] from human chromo-some 18 and ABL1 from human chromo-some 9 are the only markers mapped inthe cat from these human chromosomes.ABL1 represents the third human chro-mosome with gene homologues on feline

chromosome D4. The 35 assignments in-crease the syntenic map of the cat to 104loci, representing 18 of the 19 feline chro-mosomes. Ninety-six of the genes mappedin the cat have a human homologue. Onlytwo small chromosomes, Fl and E2, do nothave genes localized to them.

Discussion

We have added 35 genes to the feline ge-netic map by Southern blot analyses of afeline x rodent somatic cell hybrid panel.These assignments increase the markerdensity of the syntenic map of the cat to105 loci; 36 isozymes (Berman et al. 1986;Gilbert et al. 1988; O'Brien and Nash 1982),35 oncogenes (Okuda et al. 1993; Tsuji-moto et al. 1993), 12 genes involved withimmune response (Cho KW, Youn HY, Cev-ario S, O'Brien SJ, Watari T, Tsujimoto H,and Hasegawa A, submitted; Okuda M, Mi-nehata K, Setoguchl A, Nishigaki K, Watari

T, Cevario S, O'Brien SJ, Tsujimoto H, andHasegawa A, submitted; Yuhki and O'Brien1988), 2 homeobox genes (Masuda et al.1991), 1 gene encoding an rRNA (Yu et al.1980), 2 genes encoding coat-color phe-notypes (O'Brien et al. 1986), 4 copies ofthe endogenous retrovlrus RD114 (Reeveset al. 1985), and 13 miscellaneous genes.This increase in markers on the feline mapaids disease gene analyses, the study offunctional genome organization, and theextent of possible genome comparisons.

The 35 genes localized to 14 different fe-line chromosomes. Each feline chromo-some, except for E2 and Fl, now has atleast one genetic marker with a homolo-gous gene mapped in humans. Only hu-man chromosomes 16 and 19 are not rep-resented in the feline map. Human chro-mosomes 9, 13, and 18 are represented inthe cat genome by one marker each. Hu-mans have 24 chromosomes, including Y,thus 24 different syntenic groups. A direct

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Figure 2. Syntenlc map of the domestic cat (Felis calus). Ideograms depict the 19 feline chromosomes (2N =38). Gene assignments do not convey distance, order, or regional localization on the feline chromosomes, butparallel the order found In humans, as determined cytogenetlcally. Human localizations are boxed to the right ofgene symbols. Asterisks Indicate genes mapped In this study. Gene symbols reflect human nomenclature (McAlplneet al. 1994, Fasman et al. 1996).

correspondence of these 24 syntenicgroups to the 20 chromosomes (includingY) in the feline genome would require fourfeline chromosomes to represent at leasttwo human syntenic groups each. Ourdata shows that 11 feline chromosomesare represented by markers from at leasttwo different human chromosomes. Only2 of these 11 feline chromosomes, A3 andB3, are represented by more than onemarker from two different human syntenicgroups. A majority of the feline chromo-somes that have markers from more thanone human chromosome have only onemarker representing the second syntenicgroup. Most of these isolated markers arefrom extremely telomeric or centromeric

regions of the human chromosomes. Theoverall conservation of syntenic groupsbetween humans and cats is strong andmost of the asyntenic genes are fromregions with high potential for rearrange-ment.

An exception is observed with humanchromosome 8 syntenic groups. Threechromosome 8 markers have beenmapped in the cat and each localizes to adifferent feline chromosome. The threechromosome 8 markers—GSR, MOS, andMYC—are from three different regions ofhuman chromosome 8—8p, 8cen, and8q—which may explain the disruption.But most of the larger blocks of conservedsynteny between cats and humans has ex-

tended from the short arm to the long armof the human chromosome. For example,chromosome B4 has four human 12pgenes and four human 12q genes. Conser-vation of synteny across the human cen-tromere is also reflected by feline chro-mosomes Al, A2, A3, Bl, B2, B4, Dl, El,andX.

Ninety-one of the 105 genes mapped inthe cat are also localized In the mouse andhuman genomes. These 91 genes arefound on 21 different human chromo-somes, 18 different feline chromosomes,and 19 of 21 mouse chromosomes. Felinechromosome A3 genes disperse to threehuman chromosomes and to four differentmouse chromosomes (2, 6, 11, and 12). Fe-line chromosome B2 has genes from twohuman chromosomes and these genes arefound on four different mouse chromo-somes (4, 9, 10, and 17). Markers on felinechromosome B4 are found on three differ-ent mouse chromosomes. All mouse andhuman X-linked gene homologues weremapped to the feline X chromosome. Theconserved localization of genes on the Xchromosome by over 19 eutherian mam-mal species is considered a selectivemechanism to compensate for X-chromo-some inactivation (DeBry and Seldin 1996;Mouse Genome Database).

Seventy-four feline genes are Included inblocks of two or more markers from thesame human chromosome representing 15conserved syntenic segments between hu-man and cat genomes. The same 74 genehomologues are found on 17 mouse chro-mosomes; but the segments are often sepa-rated by genes from a second human chro-mosome, disrupting conserved blocksseen in the cat to 30 conserved segmentsbetween mouse and human (Copeland etal. 1993; DeBry and Seldin 1996). Thesedata suggest that the cat is two to threetimes less genomically rearranged thanthe mouse when compared to humans.

The addition of markers to the feline ge-netic map and the strong genomic conser-vation to the human genome makes thecat a valuable animal model for studyinginherited diseases. The comparative genemapping approach for disease studies is amore efficient method for candidate geneidentification than genome-wide linkagestudies, particularly in species with smallmapping projects. The cat is a model forover 30 inherited diseases found In hu-mans (Nicholas et al. 1996; Migaki et al.1992). Many of these feline disease modelscomplement murine models, and severaldisease models are unique to cat and hu-mans. The current genetic map of the cat

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provides an important resource for dis-ease research and in a carnivore represen-tative for comparative genome analyses(Modi et al. 1987; O'Brien et al. 1988).

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