A multipoint genetic linkage map of mouse chromosome 18

A Multipoint Genetic Linkage Map of Mouse Chromosome 18 KENNETH R. JOHNSON’ AND MURIEL T. DAVISON TheJackson

Laboratory, Received

February

600 Main Street, Bar Harbor, Maine 04609 17, 1992;

We have mapped 13 loci on mouse Chromosome 18 by Southern blot analysis of restriction fragment length polymorphisms among progeny from an interspecific backcross: (C57BL/6J X Mus spretus) X M. spretus. Complete haplotype analysis of 136 of these progeny was used., to establish gene order and estimate genetic distances’ between loci. The gene order (from centromere to telomere) and recombination distances (in centimorgans) were as follows: PGK-1 rs5-4.3-Tpi-1 O11.8-(Egr-1, Hmgl7-rs9)-2.1-Fgfa-2.2-Grl-l-10.1(Cdx-1, Csfmr, Pdgfrb, Pdea, Rpsl4)-2.l-Adrb-222.9-Mbp. Pgk-lrs5, Tpi-10, Hmgl7-rs9, and Rpsl4 had not been previously mapped in the mouse; Egr-1 had only been syntenically assigned to mouse Chr 18. Nine of the loci, spanning 18 CM, have homologs on the distal long arm of human Chr 5-a region rich in genes encoding growth factors and receptors. An additional previously unmapped gene, Drd-1, predicted to be on mouse Chr 18 based on its human chromosomal location, was mapped to the middle region of mouse Chr 13.

@ 1992 Academic

Press, Inc.

INTRODUCTION

The genetic map of mouse Chromosome 18 is not as well developed as the maps of most other mouse chromosomes (Davisson et uZ., 1991). The correlation between the cytologically identified Chromosome (Chr) 18 of the mouse and genes of linkage group XV (twirler, Tw; bouncy, bc; shaker-with-syndactylism, sy) was established only recently by Lane et ~2. (1981). The position of the Chr 18 centromere relative to these genes was also determined by Lane et al. (1981); additional genes have been mapped relative to these “anchor” loci. The advent of molecular methods for detecting gene polymorphisms coupled with the genetic diversity that can be exploited in interspecific and intersubspecific backcrosses has permitted multipoint linkage analysis of a large number ’

To whom

correspondence

should

be addressed. 1143

revised

April

30, 1992

of mouse genes (reviewed by Copeland and Jenkins, 1991). These new molecular methods have been used recently to improve the genetic map of Chr 18; however, no study to date has analyzed more than six genes from the same multipoint cross (Duprey et uZ., 1988; Sikela et ul., 1990; Sakai et al., 1991; Oakey et al., 1991; Cox et cd., 1991; Byrd et al., 1991). In this study, we have mapped 13 genes on mouse Chr 18 by Southern blot analysis of restriction fragment length polymorphisms (RFLPs) among progeny from an interspecific backcross between C57BL/6J and an inbred strain of Mu.s spretw (C57BL/6J X SPRET/Ei) X SPRET/Ei. Eight of the genes-fibroblast growth factor, acidic (Fgfa); glucocorticoid receptor-l (G&l); caudal type homeobox-1 (C&1); colony-stimulating factor 1 receptor (Csfmr); cGMP-phosphodiesterase alpha (Pdee); platelet-derived growth factor receptor, beta polypeptide (Pdgfrb); adrenergic receptor beta-2 (Adrb2); myelin basicprotein (Mbp)-hadbeenpositionedpreviously on mouse Chr 18 but not in a single multipoint cross. One gene-early growth response-l (Egr-1)-had been only syntenically assigned. Mouse Chr 18 (MMUl8) shares a large region of homology with the distal portion of the long arm of human Chr 5 (HSA5q)-a region rich in genes encoding growth factors and receptors. The homologs of 10 MMUl8 genes-Egr-1, Fgfa, Grl-1, Pdgfrb, Csfmr, Pdea, Adrb-2, calmodulin kinase IV (Camk4), Ia associated invariant chain (Ii), and CD14 antigen (Cd14)-have been mapped to HSA5q21-q34. We predicted that two previously unmapped genes-ribosomal protein Sl4 (Rpsl4) and dopamine Dl receptor @r-d-I)---would also map to MMUl8 based on the location of their human homologs on distal HSA5q. Here, we report our results that Rpsl4 is indeed on mouse Chr 18 but that Drd-1 is on mouse Chr 13. We also report the locations on Chr 18 of three additional previously unmapped loci that probably represent processed pseudogenes-phosphoglycerate kinase1 related sequence 5 (Pgk-1 rs5), trisephosphate isomerase-related sequence-10 (Tpi-lo), and high-mobility group protein 17 related sequence-9 (Hmgl7-rs9). 0888-7543/92 $5.00 Copyright 0 1992 by Academic Press, Inc. All rights of reproduction in any form reserved.

1144

JOHNSON

AND

TABLE DNA

Clones

and RFLPs

Used

to Map

Loci

DAVISSON

1

in the (C57BL/6J

X M. spretus)

X M. spretus

Backcross Restriction fragment sizes CkhY

Gene name

LOCUS

Che

Adrenergic receptor beta-2 Caudal type homeobox-I

Ad&Z

pTF3

Cdl-1

pBH8

Colony stimulating factor I receptor Early growth response-l

Csfmr

pcfmslO4

Egr-1

pRSV3.1

&fa

pDHl5

Fibroblast growth factor, acidic Glucocorticoid receptor-l Myelin

pSV2WREC

pHBP-1

basic protein

cGMPphosphodiesterase alpha Platelet derived growth factor receptor. beta polypept.ide High-mobility group protein 17

PI3

Insert HUman cDNA Mouse cDNA Human cDNA Mouse cDNA HUman cDNA Mouse cDNA Human cDNA Bovine cDNA

Clone source ATCC

Restriction enzyme

Reference

No. 57536

Kobilka et ~1. (19871 Duprey et al. (1988)

Dr. Peter Gruss Max Planck Inst., Gottingen, FRG ATCC No. 59292

co”ssens (1986) Sukhatme (1988)

Dr. Vikas P. Sukhatme, Howard Hughes Med. Inst., Univ. of Chicago ATCC No. 53336 Dr. Gordon M. Ringold, Stanford Univ., School Medicine ATCC No. 57458

Jaye

of

Dr. Meredithe L. Applebury, Eye Res. Lab., Univ. of Chicago ATCC No. 59734

Kamholz (1986) Danciger (1990)

s

P.91

4.2 -

2.5, 1.9

MspI

!g,g

3.6, 1.9

P&l

-2.4

1.3, 0.9

MspI

g5, -1.5

10.0

PstI

5.J, 3.5, 0.45

4.5, 3.5, 0.45

et al.

‘g, 2, z,

et al.

0.6 4.4,9, g, z, -2.1

4.6, 3.1, 2.7. 0.6 4.4, 4.0, 3.9, 3.1, 2.7, 2.5, 2.0 5.2, 2.8

et al. et al.

et al.

et a[.

pRP41

HUnIan cDNA

Hmg 17 and related sequences

pMl7c

MO”%? cDNA

Dr. Michael Bustin, NatI. Cancer Inst., Bethesda, MD

Landsman (19881

et aL.

P&l and related seq”E!nlx!s

pHPGK-7e

Human cDNA

ATCC

Michelson (1983)

et al.

Taql

Rpsl4 and related sequences

pcs14-1

Chinese hamster cDNA

Dr. Donald ,J. Roufa, Kansas State Univ., Manhattan, KS

Nakamichi (1983)

et al.

MS/II

Triose phosphate isomerase-1

Tpi-1 and related s‘que!nces

pMurTP1

Mouse cDNA

ATCC

Cheng et al. (1990)

PstI

Dopamine

D&l

G-36

Rat cDNA

O’Dowd et al. (1990)

PUUII

reductase

Dhfr

gamma

TCrg

pLTRdhfr26 pMtcrg

Mouse cDNA Mouse cDNA

Dr. Brian F. O’Dowd, Univ. of Toronto, Ontaria, Canada ATCC No. 37295

Phosphoglycerate kinase-l

Ribosomal

protein

Sl4

Dl receptor

Dihydrofolate T-cell receptor chain

No. 57222

No. 63090

Dr. cJ. G. Seidman, Harvard Medical

a Underlined fragments probes for Hmgl7, Pgk-I, are underlined.

School

Gronwald t 1988)

SPRET/Ei

&oRI

eta/z. (1986)

Danielsen (1986)

C57BL/6J

Chang et al. (1978) Owen et al. (1986)

MspI

MspI

2.6

c,‘&l 7.4, 6.0, 5.4, 5.1, 4.9, 4.7, 4.4, 4.3,4.2, 4.0, 3.6, 3.2, 2.9, 2.83 2.6, 2.4, 2.1, 1.9, 1.5, 1.1, Q, 0.8 9.0,5.9, E, 4.0, 3.6, 3.0, 2.9, 1.8 14.0, 7.2, 4.2, 3.4, 2.6, 2.2, s, 1.8, 1.7,1‘4, 0.95, 0.70, 0.55 13.0, 8.0, 7.0, 4.9, 4.4, g, 3.1, 2.9, 2.7 4.1 -

9.2, c, 2.7, 1.7, 1.2 8.9, 7.J 5.6, 3.3

6.0. 2.6

12.0, 8.0, 6.6, 4.7, 4.4, 4.2, 4.0, 3.4, 3.2, 2.9, 2.7, 1.9, 1.7, 1.3, 1.2, 1.1

8.6, 7.4,6.8, 4.0, 2.4, 2.0 9.2, 8.2, 8.0, 3.4, 2.8, 2.5, 1.8, 1.7. 1.45, 0.95, 0.75

12.0, 9.0, 8.2, 7.6, 6.2, 4.9, 4.5, 3.8, 3.6, 3.1, 2.7 4.6

12.0, 6.0, 2.7, 1.5 10.5, 8.9, 8.5. 5.6, 3.3

were

unique to C57BL/6J alleles; their presence or absence was used to determine backcross genotypes. The cDNA Rpsl4, and Tpi-1 detect multiple fragments representing several independently segregating loci; only those on Chr 18

The 13 genes that we mapped to Chr 18 span 56 CM, which is almost the entire estimated genetic length of the chromosome (GBASE, 1992). Our resulting multipoint genetic map and panel of typed DNAs from the 136

backcross mice will provide the basis for further improvement of the genetic resolution of mouse Chr 18. A better genetic map will aid in the construction of a physical map and will also help identify candidate genes for the

GENETIC

MAP

OF MOUSE

CHROMOSOME

1145

18

imum likelihood using the computer program MAPMAKER (Lander et cd.,1987).

RESULTS

2.5

Grl-1

Egr- 7 Pst

Pst

I

Csfmr Msp I

I

nfsp 1

4.6 CL 2.2 2.6 2.6

Fgfa MS/J

Pdgfrb I

Adrb-2

MS/J I

EcoR

Drd-7

Pdea I

Taq

I

Pvll

I I

FIG. 1. Southern blot analysis of single-locus RFLPs. Gene symbols and informative restriction enzymes are indicated below each panel. These RFLPs were used to identify progeny genotypes of the (C57BL/6J X SPRET/Ei) X SPRET/Ei interspecific backcross. In each panel, the homozygous SPRET/Ei phenotype is shown in the first lane and the heterozygous C57BL/6J X SPRET/Ei FI phenotype is shown in the second lane. Molecular weight estimates (in kb) of selected DNA fragments are given to the right of each panel. Underlined fragments originated from the C57BL/6J genome; their presence or absence was used to determine genotypes.

molecular analysis of mutations medical significance. MATERIALS

AND

that have potential

bio-

METHODS

All mouse stocks used in this study were obtained from the Mice. Mouse Mutant Resource Colony of The Jackson Laboratory (Bar Harbor, ME). The interspecific backcross has been previously described (Johnson er al., 1992). Mice from an inbred strain of M. spretus (SPRET/Ei) were mated with C57BL/6J; FI females were then backcrossed to SPRET/Ei males. All mice were maintained under standard Jackson Laboratory conditions. Southern blot analysis. Table 1 lists the DNA clones and their sources and describes the RFLPs that were used to identify and map foci in the interspecific backcross. Only the cDNA inserts from these clones were used as probes. Probe labeling, Southern blotting, and hybridization procedures were as previously described (Johnson er al., 1992). Statistical analysis. Genetic tion analysis of the interspecific and recombination frequencies

linkage was determined by segregabackcross progeny. Map locations were calculated by the method of max-

DNA restriction fragment length phenotypes of the interspecific backcross progeny are shown in Fig. 1 for 10 cDNA probes that hybridized with single-copy genes thought to be on mouse Chr 18. For each locus, progeny genotype assignments were based on the presence or absence of diagnostic DNA fragments that originated from the genome of the nonrecurrent backcross parent (C57BL/6J). Four additional cDNA probes (encoding Tpi-1, Pgk-1, Rpsl4, and Hmg17) each detected multiple DNA fragments representing several independently segregating loci (Fig. 2). Those DNA fragments that mapped to Chr 18 (as determined by their linkage with previously mapped reference markers; Table 2) are identified by arrows to the right of each panel; their presence or absence was used to assign progeny genotypes for the loci we designate Tpi-10, Pgk-lrs5, Rpsl4, and Hmgl7-rs9. Recombination frequencies between loci are listed in Table 2. Thirteen of the 14 tested loci were linked on Chr 18. We mapped the exceptional locus, Drd-1, between the prepositioned reference loci Tcrg and Dhfr on mouse Chr 13 (Table 2). For Chr 18, recombination was not detected between Hmgl7-rs9 and Egr-1 nor between any of the following five genes: Pdea, Rpsl4, Pdgfrb, Cdx-1, and Csfmr. We treated each of these two gene clusters as a single locus in the haplotype distribution analysis of 136 backcross mice shown in Fig. 3. The gene order and genetic distances that we estimated do not differ significantly from the published results of previous genetic linkage studies of mouse Chr 18 (Duprey et al., 1988; Sikela et al., 1990; Sakai et al., 1991; Oakey et aZ,, 1991; Cox et al., 1991; Byrd et al., 1991) for those loci that could be compared. We detected no statistically significant deviations from the expected 1:l segregation of alleles at any of the loci. Assuming the order of loci shown in Fig. 3, there were no observed double crossovers, indicating a high degree of positive interference. Oakey et al. (1991), who also analyzed a AI. spretus interspecific backcross, likewise found no double crossovers on Chr 18; however, one or two double crossovers have been reported in intersubspecific crosses (Sikela et al., 1990; Sakai et al., 1991; Byrd et al., 1991). These results suggest that interspecific hybrids may exhibit a higher degree of positive chiasma interference on Chr 18 than do intraspecific or intersubspecific hybrids, as has been shown for mouse Chr 12 (Seldin et al., 1989). DISCUSSION

Our multipoint

linkage map of 13 genes on mouse Chr haplotype analysis of 136 mice provides a solid framework for high-

18 based on the complete

backcross

1146

JOHNSON

AND

DAVISSON

6.6

6.6

2.3 2.0

2.3

0.6

Tpi-

Rpsl4

10

Hmg77- 9

Msp 1

Pstl

Taq

1

FIG. 2. Southern blot analysis of multilocus RFLPs. The cDNA probes for Z”i-2, Pgk-1, &x14, and Hmg17 each detected multiple, dispersed loci. Gene symbols for those loci that mapped to mouse Chr 18 and the restriction enzymes used to identify them are given below each panel. The symbol Hmgl7.rs9 has been approved by the Committee for Standardized Genetic Nomenclature in Mice for the gene shown in the figure as Hmgl7-9. Each panel illustrates the DNA restriction fragment patterns of four progeny from the (C57BL/6J x SPRET/Ei) X SPRET/Ei interspecific backcross. The DNA fragments corresponding to the Chr 18 loci are indicated by arrows on the right side of each panel. These fragments originated from the C57BL/6J genome; their presence or absence was used to determine backcross progeny genotypes. Molecular weight estimates (in kbl are shown to the left of each panel.

resolution genetic dissection of this chromosome. We have focused on mouse Chr 18 because this chromosome has not been well studied, because it contains many important genes encoding growth factors and receptors, and because several biomedically important spontaneous mutations have been mapped to it.

We tested 136 backcross mice (resolution limit ~1 CM) and observed no recombination between the genes Cdx-1, Pdgfrb, Csfmr, Rpsl4, and Pdea. This observation suggests that this entire cluster of five genes is contained in less than 2 Mb of DNA, assuming that recombination occurs randomly along the chromosome and that 1 CM is

TABLE Recombination Chromosome 18 18 18 18 18 18 18 18 18 18 18 18 13 13

Locus Pgk-lrs5 Tpi-IO Hmgl7-rs9 Egr-1 Fgfa G&l Pdea Rpsl4 Pdgfrb Cdx-1 Csfmr Ad&2 Tug Drd-1

2

Frequencies

paira

between

Loci % Recombination

Recombinant/total 6/140 171144 o/140 31140 3/139 14/139 o/144 o/144 01140 o/140 3/141 32/140 231117 34/126

Tpi-10 Hmgl7-rs9 Egr- 1 Fgfa Grl-I Pdea Rpsl4 Pdgfrb Cdx- 1 Csfmr Ad&2 Mb Drd-1 Dhfr

a The loci are listed in the order determined by maximum locus nearest the centromere is listed first. * This number represents the upper 95% confidence limit the total number of mice examined.

likelihood expressed

multipoint

analysis,

as 100 X r, where

minimizing

r is calculated

(SE)

4.3 (1.7) 11.8 (2.71 <2.1b 2.1 (1.2) 2.2 (1.2) 10.1 (2.61 <2.0b <2.0b <2.1b <2.1b 2.1 (1.2) 22.9 (3.6) 19.7 (3.71 27.0 (4.0) the number from

the formula

of double

crossovers.

The

(1 - r)” = 0.05 and n is

GENETIC

Number

of Mice

223..AQ~~U 62 6

15

3

ULdLU 3

MAP

13

2

OF

MOUSE

2Lu 32

FIG. 3. Haplotype distribution of 136 interspecific backcross mice for 13 loci on Chr 18. Solid squares represent C57BL/6J alleles; open squares, SPRET/Ei alleles. Tested loci are listed to the left of each row of squares. Those genes that did not recombine are grouped together as single loci for haplotype analysis-Egr-1 and Hmgl7-w9 as one locus and Cdx-1, Csfmr, Pdea, Pdgfrb, and Rpsl4 as another. The number of mice with each haplotype is given below each column. Gene order was determined by multipoint maximum likelihood analysis. Assuming this order, no double crossovers were observed. Note that the number of recombinants between locus pairs in this figure does not agree in all cases with the number of recombinants listed in Table 2 Only mice that were typed for all 13 loci (136) are included in this figure; we were able to type more mice for individual locus pairs (Table 2).

roughly equivalent to 2 Mb of DNA. However, genetic distances are known to be influenced by factors other than physical distance. For instance, the gene cluster that we observed could be due to repressed recombination resulting from a chromosomal inversion in jVl. spretus relative to C57BL/6J. Evidence from the homologous genes in humans, however, strongly suggests that at least three of these genes are in close physical proximity. In humans, the PDGFRB gene (Pdgfrb in mice) is located less than 0.5 kb from the CSFlR gene (C&V in mice) based on nucleotide sequence analysis (Roberts et al., 1988). Recently, Pdgfrb and Csfmr were also shown to be physically associated in mice (Eccles, 1991). Using radiation hybrid mapping, Warrington et al. (1991) were unable to define order between RPS14 (Rpsl4 in mice) and CSFlR and estimated that these genes are less than 1 Mb apart. To exclude the possibility that the observed gene clustering in mice is due to a M. spretus inversion relative to C57BL/6J, we plan to genetically map the same five loci in a backcross using M. muscu1u.s castaneus. Clustering of the genes in this cross would support the idea of close physical linkage, which could then be confirmed using pulsed-field gradient gel electrophoresis. As part of our effort to increase the efficiency of genetic mapping in the mouse, we are analyzing several cDNA probes that detect dispersed members of multigene families. Four of these multilocus cDNA probesencoding Pgk-1, Tpi, Rpsl4, and Hmgl7-detect loci that we have mapped to Chr 18, as well as several additional independently segregating loci. We designate the Pgk-1 -related locus that we mapped to Chr 18 Pgk-1 rs5 --

CHROMOSOME

1147

18

(rs for related sequence) to differentiate it from four previously mapped Pgk-1 pseudogenes (Adra et al., 1988) and to signify that we have not definitively shown this locus to be a pseudogene. The functional Pgk-1 gene is on the mouse X chromosome. The Tpi locus we identified on Chr 18 was given the new locus designation Tpi10 to differentiate it from nine previously described members of the mouse Tpi multigene family, none of which mapped to Chr 18 (Siracusa et uZ., 1991). The functional gene, Tpi-1, is on mouse Chr 6. It is not clear whether the other Tpi- loci are pseudogenes or related sequences. The multigene family of chromosomal protein HMG17 comprises the largest known human retropseudogene family; the single functional gene has been localized to human Chr lpl2-p34 (Landsman et ul., 1989). Southern blot analysis has shown that HMG-17 is also a multigene family in mice (Landsman et ul., 1986), but individual members of this family have not been previously described or mapped. We have mapped 15 members of the Hmg17 gene family in the mouse genome (our unpublished data) and here describe one that maps to Chr 18 and that we designate Hmgl7-rs9. Hmgl7-rs9 is probably not the functional murine Hmg17 gene, because murine Chr 18 has no known homologies with human Chr lpl2-~34, the location of the functional human HMG-17 gene. Unt,il the functional Hmg17 gene is identified, we propose to designate the genes we map as related sequence genes; hence, Hmgl7-rs9. HSA 5q ten

MMU 18

ARSB HTRIA piJ

fiiiiiq

HMGCR

: 5cmql4

lL4,us IL3 CSFZ ANX6

.Pgk-In5 .Tpi-10

.Egr-1, .Fgfa fxI

Hmgl7-rs9

&a%I, Csfmr, ,Pdea, Rpsl4 Adrb-2

-

m : 5q23.q31

EGRl FGFA GRL

Pdgfrb

,CSFlR PDGFRB RPSl4 PDEA ADRB2

22.9

2 5q31-q34 DRDl 23 TLA3

: sq21.qter

FIG. 4. Comparison of ordered maps of HSA5q and MMUl8, showing selected MMUll and MMUl3 genes. Only MMUl8 genes mapped in this study are shown. The human map is based on the deletion map in Huebner et al. (1990), the radiation hybrid and deletion map in Warrington et al. (1991), and the Report of the Chromosome 5 Committee Workshop (Westbrook et al., 1991).

1148

JOHNSON

AND

Although the human genome harbors multiple RPSl4 processed pseudogenes, Nakamichi et oz. (1986) were able to identify the transcriptionally active RPSl4 gene and map it to HSA5q23-5q33. We have mapped eight Rpsl4-related loci in the mouse genome (our unpublished data), and one of these loci mapped to Chr I8 in a region of known homology to HSA5q23-5q33. Because of the large number of evolutionarily conserved genes in these regions of HSA5q and MMUI8, we think it is likely that this locus represents the functional, transcriptionally active mouse gene and therefore provisionally designate it Rpsl4. Mouse Chr 18 shares conserved regions with two human chromosomes, the distal ends of the long arms of Chr 5 (5q21-q34) and Chr 18 (18q22-qter). The 5q conserved region spans approximately 18 CM in the central portion of mouse Chr 18. One of the three human Chr 18 genes, Mbp, maps to the distal end of mouse Chr 18, in our cross 23 CM beyond the most distal human Chr 5 homolog, Adrb-2. Thus, the data so far suggest that mouse Chr 18 is composed of two discrete segments conserved in two human chromosomes. The other two Chr 18 homologs, peptidase-1 (Pep-l) and T-cell protein tyrosine phosphatase (Ptpt), are only syntenically assigned to mouse 18, and we predict that they are likely to map near Mbp. The majority of mouse Chr 18 human homologs map to the distal half of HSA5q between bands 5q21 and q34. The order within this segment appears to be conserved in mouse and human chromosomes (Fig. 4). The eight homologous loci mapped genetically in our cross are in the same centromere-to-telomere order in HSA5q, with one possible exception. The natural deletion map of Huebner et al. (1990) places CSFlR and PDGFRB proximal to ADRB2, while Warrington et aZ. (1991) propose the reverse order based on radiation hybrid and natural deletion data. The order in MMUl8 predicts that ADRB2 is the more distal locus in HSA5q. The simplest interpretation of previous evidence is that human 5q contains three conserved segments with clusters of homologous loci from mouse Chr 13 (MMU13) in proximal 5q, MMUll in central 5q, and MMUl8 in distal 5q (Johnson andDavisson, 1991); however, recent findings suggest a more complex arrangement of homologies (Fig. 4). For example, our map location for Drd-1 on MMU13 and the localization of DRDl on the most distal region of HSA5q (Warrington et al., 1991) now suggest that there is an additional MMU13 conserved segment at the distal end of HSA5q. We mapped Drd-1 near interleukin-9 (IL-g), in a region of MMUI3 that is proximal to the group of genes forming the previously identified conserved segment with proximal HSA5q (GBASE, 1992). The similar map locations of Drd-1 and Il-9 (Mock et al., 1990) on MMU13 suggest that IL9 will map close to DRDl on the distal end of HSA5q. Indeed, the human homolog IL9 recently has been mapped to HSA5q31-q35 (Modi et al., 1991). While comparative gene mapping is clearly a powerful appreach, prediction of linkage on the basis of homology

DAVISSON

must always be confirmed by mapping studies, as shown by our results with Drd-1. Our Chr 18 map provides a basis for future high-resolution mapping studies of mouse Chr 18. The panel of DNAs with recombinational events in defined intervals is a resource that will enable us to rapidly map additional Chr 18 genes. Each additional gene mapped will subdivide the intervals, improving the linkage map of Chr 18, and, consequently, greatly aid subsequent physical mapping efforts. Identification of these and additional loci will also provide a valuable resource for mapping new mutations located on mouse Chr 18 and, ultimately, for defining new mouse models of human conditions. Genetic mapping was instrumental in determining that shiverer (shi) is a mutation of myelin basic protein (Mbp) (Roach et al., 1985) and will likely play an important role in determining the molecular bases of other biomedically important mutations on Chr 18. ACKNOWLEDGMENTS We thank Drs. P. Gruss, V. P. Sukhatme, G. M. Ringold, M. L. Applebury, M. Bustin, D. J. Roufa, B. F. O’Dowd, and J. G. Seidman and their affiliated institutions listed in Table 1 under Clone Source for their generous gifts of DNA probes. We thank Sue Cook for technical assistance and Linda Neleski for help in preparing the manuscript. We also thank Drs. Joe Nadeau and Ben Taylor for critical review of the manuscript. This research was supported by National Institutes of Health Grant RR01183 and a gift from the Eleanor Naylor Dana Charitable Trust.

REFERENCES Adra, C. N., Ellis, N. A., and McBurney, M. W. (1988). The family of mouse phosphoglycerate kinase genes and pseudogenes. Somat. Cell Mol. Genet. 14: 69-81. Byrd, L., Grossmann, M., Potter, M., and Shen-Ong, G. L. C. (1991). Chronic multifocal osteomyelitis: A new recessive mutation on Chromosome 18 of the mouse. Genomics 11: 794-798. Chang, A. C. Y., Nunberg, J. H., Kaufman, R. J., Erlich, H. A., Schimke, R. T., and Cohen, S. N. (1978). Phenotypic expression in E. coli of a DNA sequence coding for mouse dihydrofolate reductase. Nature 275: 617-624. Cheng, J., Mielnicki, L. M., Pruitt, S. C., and Maquat, L. E. (1990). Nucleotide sequence of murine triosephosphate isomerase cDNA. Nucleic Acids Res. 18: 4261. Copeland, N. G., and *Jenkins, N. A. (1991). Development and applications of a molecular genetic linkage map of the mouse genome. Trends Genet. 7: 113. Coussens, L., Van Beveren, C., Smith, D., Chen, E., Mitchell, R. L., Isacke, C. M., Verma, I. M., and Ullrich, A. (1986). Structural alteration of viral homologde of receptor proto-oncogene fms at carboxyl terminus. Nature 320: 277-280. Cox, R. D., Copeland, N. G., Jenkins, N. A., and Lehrach, H. (1991). Interspersed repetitive element polymerase chain reaction product mapping using a mouse interspecific backcross. Genomics 10: 375384. Danciger, M., Kozak, C. A., Li, T., AppIebury, M. L., and Farber, D. B (1990). Genetic mapping demonstrates that the a-subunit of retinal cGMP-phosphodiesterase is not the site of the rd mutation. EXP. Eye Rex 51: 185-189. Danielsen, M., Northrop, J. P., and Ringold, G. M. (1986). The mouse glucocorticoid receptor: Mapping of functional domains by cloning,

GENETIC

sequencing and expression of wild-type teins. EMBOJ. 5:2513-2522. Davisson, M. T., Johnson, tanabe, T. (1991). Mouse s301-s305.

K. R., Seldin, chromosome

and

mutant

MAP

OF

receptor

MOUSE

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