SHORT COMMUNICATION Genetic Mapping of a New Homeobox Gene to Mouse Chromosome 7 KENNETHR. JOHNSON,*'1 SANGWEILu, t MICHAELT. MURTHA,t FRANKH. RUDDLE,t AND MURIELT. DAVlSSON* *The Jackson Laboratory, Bar Harbor, Maine 04609; and tBiology Department, Yale University, New Haven, Connecticut 06520 Received July 7, 1992; revised September 6, 1992
A newly identified homeobox gene designated Dbx h a s b e e n m a p p e d to m o u s e C h r o m o s o m e (Chr) 7. T h i s gene is expressed in a restricted manner in developing m o u s e b r a i n a n d s p i n a l c o r d a n d h a s a m i n o a c i d sequence similarities with members of the homeobox g e n e f a m i l y s u c h a s D r o s o p h i l a 1-12.0 a n d m o u s e H / x . U s i n g a f r a g m e n t o f t h e D b x c D N A as a p r o b e , a P s t I r e s t r i c t i o n f r a g m e n t l e n g t h p o l y m o r p h i s m w a s u s e d to determine genotypes of 144 progeny from an interspecific backcross. Segregation analysis revealed linkage of Dbx with six prepositioned reference loci on mouse C h r 7. N o r e c o m b i n a t i o n w a s o b s e r v e d b e t w e e n D b x a n d Odc-rs6, i n d i c a t i n g t h a t D b x l i e s a p p r o x i m a t e l y 2 5 c M d i s t a l to t h e C h r 7 c e n t r o m e r e i n a r e g i o n t h a t h a s conserved linkage relationships with regions of human C h r s 1 1 a n d 1 9 . © 1992 AcademicPress, Inc.
Several classes of transcription factors have been implicated in the control of development since the discovery of the Antennapedia homeobox genes in 1983 (14). The original A-type genes, now known as group 1 homeobox genes, are broadly distributed throughout metazoan animals. These genes are characterized by the presence of a conserved 183-bp sequence encoding a helixturn-helix motif termed the homeobox, which confers DNA binding specificity on the protein products. The most closely related A-type genes are organized into four tightly linked clusters that map to four different chromosomes in the human and mouse genomes. The clusters are designated Hox-1, -2, -3, and -4 and map to mouse Chromosomes (Chrs) 6, 11, 15, and 2, respectively. The homologous loci (HOX1, 2, 3, and 4) in the human genome map to human Chrs 7, 17, 12, and 2. The average number of genes within a cluster is 9 and the total number of genes in the HOX group is 38. These genes are expressed in a variety of tissue types, but not anterior to the hindbrain-midbrain junction. Several other transcription factor genes with helixturn-helix domains, distantly related to the A type (Hox) genes, have been shown to be expressed in the telencephalon and mesencephalon. Examples are the 1 To w h o m r e p r i n t requests should be addressed.
paired box, POU, and engrailed genes. We (F.H.R. and co-workers) have recently described additional genes related by sequence to the A-type genes and the mouse Hlx (H2.0-1ike homeobox) gene (1), but expressed in the anterior central nervous system, and have provisionally referred to them as MMoxA, MMoxB, and MMoxC (13). In this report, we describe the mapping of one of these newly discovered genes, MMoxC, which we now designate Dbx (developing brain homeobox gene), to mouse Chr 7. The Dbx homeodomain shares 87% amino acid sequence homology with chicken CHoxE, (homeobox E), 66% with that of Drosophila H2.0, 69% with mouse Hlx, and 38% with the Drosophila Antennapedia gene (12). Dbx is expressed in a restricted manner in regions of the embryonic central nervous system, including highly localized regions in the telencephalon, diencephalon, mesencephalon, hindbrain, and spinal cord. A probe for Dbx was isolated by screening a 10.5-day mouse embryo cDNA library with the MMoxC probe, a PCR-amplified cDNA fragment (13). A positively hybridizing cDNA clone was confirmed to encode Dbx by DNA sequence analysis (12). A 220-bp HaeIII fragment from this Dbx cDNA was used as the probe (designated SAC-l) for the genetic mapping study described here. Dbx was mapped to mouse Chr 7 using a previously described panel of 144 progeny DNAs from an interspecific backcross between an inbred strain of Mus spretus (SPRET/Ei) and the laboratory strain C57BL/6J (B6) --(C57BL/6J X SPRET/Ei) F1 females X S P R E T / E i (SPRET) males (9). On this backcross panel we (K.R.J. and M.T.D.) have already mapped 230 polymorphic loci randomly distributed over all 19 autosomes and the X chromosome. Probe labeling, Southern blotting, and hybridization conditions used in the present study were the same as previously described (9). Only a single gene was detected using the SAC-1 probe, as evidenced by single hybridizing DNA fragments on Southern blots of mouse genomic DNA (both B6 and SPRET) digested with B a m H I (7.5 kb), EcoRI (4.2 kb), HindIII (4.5 kb), and PvuII (4.6 kb) (data not shown). The SAC-1 probe detected a PstI restriction fragment length polymorphism (RFLP) between B6 and S P R E T genomic DNA. PstI fragments were 1.5, 1.2, and 0.7 kb in B6 DNA and 3.0, 1.5, and 1.2
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] 4 , 1107-1109 (1992) 0888-7543/92 $5.00 Copyright © 1992 by Academic Press, Inc. All rights of reproduction in any form reserved. GENOMICS
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TABLE 1A
kb
Linkage of Dbx with Six Prepositioned Reference Loci on Mouse Chr 7
3.0
Locus pair a
Total recombinants
% Recombination (SE)
Pmv-4, Gpi-1 Gpi-1, Odc-rs6 Odc-rs6, Dbx Dbx, Mpmv-1 Mpmv-1, Tyr Tyr, Odc-rs7
10/85 18/136 0/141 10/136 19/96 4/89
11.8 (3.5) 13.2 (2.9)
A newly identified homeobox gene designated Dbx h a s b e e n m a p p e d to m o u s e C h r o m o s o m e (Chr) 7. T h i s gene is expressed in a restricted manner in developing m o u s e b r a i n a n d s p i n a l c o r d a n d h a s a m i n o a c i d sequence similarities with members of the homeobox g e n e f a m i l y s u c h a s D r o s o p h i l a 1-12.0 a n d m o u s e H / x . U s i n g a f r a g m e n t o f t h e D b x c D N A as a p r o b e , a P s t I r e s t r i c t i o n f r a g m e n t l e n g t h p o l y m o r p h i s m w a s u s e d to determine genotypes of 144 progeny from an interspecific backcross. Segregation analysis revealed linkage of Dbx with six prepositioned reference loci on mouse C h r 7. N o r e c o m b i n a t i o n w a s o b s e r v e d b e t w e e n D b x a n d Odc-rs6, i n d i c a t i n g t h a t D b x l i e s a p p r o x i m a t e l y 2 5 c M d i s t a l to t h e C h r 7 c e n t r o m e r e i n a r e g i o n t h a t h a s conserved linkage relationships with regions of human C h r s 1 1 a n d 1 9 . © 1992 AcademicPress, Inc.
Several classes of transcription factors have been implicated in the control of development since the discovery of the Antennapedia homeobox genes in 1983 (14). The original A-type genes, now known as group 1 homeobox genes, are broadly distributed throughout metazoan animals. These genes are characterized by the presence of a conserved 183-bp sequence encoding a helixturn-helix motif termed the homeobox, which confers DNA binding specificity on the protein products. The most closely related A-type genes are organized into four tightly linked clusters that map to four different chromosomes in the human and mouse genomes. The clusters are designated Hox-1, -2, -3, and -4 and map to mouse Chromosomes (Chrs) 6, 11, 15, and 2, respectively. The homologous loci (HOX1, 2, 3, and 4) in the human genome map to human Chrs 7, 17, 12, and 2. The average number of genes within a cluster is 9 and the total number of genes in the HOX group is 38. These genes are expressed in a variety of tissue types, but not anterior to the hindbrain-midbrain junction. Several other transcription factor genes with helixturn-helix domains, distantly related to the A type (Hox) genes, have been shown to be expressed in the telencephalon and mesencephalon. Examples are the 1 To w h o m r e p r i n t requests should be addressed.
paired box, POU, and engrailed genes. We (F.H.R. and co-workers) have recently described additional genes related by sequence to the A-type genes and the mouse Hlx (H2.0-1ike homeobox) gene (1), but expressed in the anterior central nervous system, and have provisionally referred to them as MMoxA, MMoxB, and MMoxC (13). In this report, we describe the mapping of one of these newly discovered genes, MMoxC, which we now designate Dbx (developing brain homeobox gene), to mouse Chr 7. The Dbx homeodomain shares 87% amino acid sequence homology with chicken CHoxE, (homeobox E), 66% with that of Drosophila H2.0, 69% with mouse Hlx, and 38% with the Drosophila Antennapedia gene (12). Dbx is expressed in a restricted manner in regions of the embryonic central nervous system, including highly localized regions in the telencephalon, diencephalon, mesencephalon, hindbrain, and spinal cord. A probe for Dbx was isolated by screening a 10.5-day mouse embryo cDNA library with the MMoxC probe, a PCR-amplified cDNA fragment (13). A positively hybridizing cDNA clone was confirmed to encode Dbx by DNA sequence analysis (12). A 220-bp HaeIII fragment from this Dbx cDNA was used as the probe (designated SAC-l) for the genetic mapping study described here. Dbx was mapped to mouse Chr 7 using a previously described panel of 144 progeny DNAs from an interspecific backcross between an inbred strain of Mus spretus (SPRET/Ei) and the laboratory strain C57BL/6J (B6) --(C57BL/6J X SPRET/Ei) F1 females X S P R E T / E i (SPRET) males (9). On this backcross panel we (K.R.J. and M.T.D.) have already mapped 230 polymorphic loci randomly distributed over all 19 autosomes and the X chromosome. Probe labeling, Southern blotting, and hybridization conditions used in the present study were the same as previously described (9). Only a single gene was detected using the SAC-1 probe, as evidenced by single hybridizing DNA fragments on Southern blots of mouse genomic DNA (both B6 and SPRET) digested with B a m H I (7.5 kb), EcoRI (4.2 kb), HindIII (4.5 kb), and PvuII (4.6 kb) (data not shown). The SAC-1 probe detected a PstI restriction fragment length polymorphism (RFLP) between B6 and S P R E T genomic DNA. PstI fragments were 1.5, 1.2, and 0.7 kb in B6 DNA and 3.0, 1.5, and 1.2
1107
] 4 , 1107-1109 (1992) 0888-7543/92 $5.00 Copyright © 1992 by Academic Press, Inc. All rights of reproduction in any form reserved. GENOMICS
1108
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TABLE 1A
kb
Linkage of Dbx with Six Prepositioned Reference Loci on Mouse Chr 7
3.0
Locus pair a
Total recombinants
% Recombination (SE)
Pmv-4, Gpi-1 Gpi-1, Odc-rs6 Odc-rs6, Dbx Dbx, Mpmv-1 Mpmv-1, Tyr Tyr, Odc-rs7
10/85 18/136 0/141 10/136 19/96 4/89
11.8 (3.5) 13.2 (2.9)
