| First Author | Frohman MA | Year | 1993 |
| Journal | Mouse Genome | Volume | 91 |
| Issue | 2 | Pages | 323-25 |
| Mgi Jnum | J:12770 | Mgi Id | MGI:60989 |
| Citation | Frohman MA, et al. (1993) Mapping of Gbx-1 to mouse Chromosome 5 and Gbx-2 to mouse Chromosome 1. Mouse Genome 91(2):323-25 |
| abstractText | Full text of Mouse Genome contribution: MAPPING OF GBX-1 TO MOUSE CHROMOSOME 5 AND GBX-2 TO MOUSE CHROMOSOME 1. Michael A. Frohman(1,3), Mary E. Dickinson(2,4), Brigid L.M. Hogan(2), and Gail R. Martin(1). 1 Dept Anatomy, University of California at San Francisco, San Francisco, CA 94143; 2 Dept. Cell Biology, Vanderbilt University Medical School, Nashville, TN 37232-2175; 3 Present address: Dept Pharmacological Sciences, SUNY at Stony Brook, Stony Brook, NY 11794-8651. To whom correspondence should be addressed. 4 Current address: Dept. Cell and Developmental Biology, Roche Institute of Molecular Biology, Roche Research Center, Nutley, NJ 07110. INTRODUCTION The murine genes Gbx-1 and Gbx-2 encode related homeodomain-containing proteins that are unrelated to any specific homeodomain-containing proteins known to exist in Drosophila (1; Fig. 1). The murine genes are expressed in a restricted manner at several stages of development, in particular during gastrulation and in the developing CNS, which has prompted the designation "gastrulation-brain- homeobox", or Gbx (1). A chicken cognate for Gbx-1 (CHox-7; see ref. 2) was previously reported, and a Xenopus cognate for Gbx-2 has also been isolated (1). In addition, a recent study reported two murine partial homeodomain sequences that were identical to each other and to Gbx-1 and -2 throughout the 25 amino acid peptide described (3). To begin to investigate whether mutations of Gbx-1 and -2 exist, we determined their chromosomal locations using interspecific backcross analyses. MATERIALS AND METHODS The Gbx cDNAs were cloned as described elsewhere (1). Gbx-1 genomic fragments were identified using a 376 bp 3' untranslated cDNA probe beginning 4 bp 3' of the stop codon and ending 5 bp 5' of the poly-A tail. Gbx-2 genomic fragments were identified using a 610 bp 3' untranslated cDNA probe beginning 21 bp 3' of the stop codon and ending 20 bp 5' of the poly-A tail. The probes used to detect En-1 and-2 genomic fragments have been described previously (4). Genomic fragments were detected using Southern hybridization under conditions previously described, using a final wash solution of 0.2 x SSC/ 0.1% SDS at 65 degrees C (5). Segregation patterns were determined using a (C57Bl/10 Nimr - +/SeyMH x Mus spretus) Fl x C57Bl/10 Nimr backcross that has been described previously (6). RESULTS cDNA probes containing the 3' untranslated regions of Gbx-1 and -2 were used to identify restriction fragment length varients (RFLVs) between M. musculus and M. spretus. For Gbx-1, an RFLV between C57Bl/10 Nimr - +/SeyMH and M. spretus was identified using HindIII. In C57B1/10, a 5.2 kb fragment was observed; in M. spretus, a 2.8 kb fragment was observed. For Gbx-2, an RFLV was identified using Pst I. In C57B1/10, a 3.1 kb and a 1.6 kb fragment were observed; in M. spretus, a 1.0 kb fragment was observed. Figure 1. (Legend). Homeodomain and partial carboxy-terminus sequences for Gbx-2 (G2), -1 (G1), and the chicken gene Chox-7 (C7). Only a partial homeodomain sequence is available for Gbx-1. Shaded residues are identical to those shown for Gbx-2. The segregation patterns of the Gbx-1 and Gbx-2 RFLVs found were determined for a panel of 30 backcross progeny characterized previously with a variety of probes (6). The segregation pattern observed for Gbx-1 was similar but not identical to that found for an unrelated gene that had been mapped independently to chromosome 5 (M.E.D. and R.P. Roychik, unpublished results). A segregation pattern was then determined for En-2, which is an unrelated homeobox-containing gene on chromosome 5 (5). To accomplish this, an RFLV was found for En-2 using Hind III; fragments of 10 kb (C57Bl/10) and 8.5 kb (M. spretus) were observed. The segregation patterns of Gbx-1 and En-2 were found to be identical to each other in the 28 mice examined (Table 1). This result indicated that Gbx-1 is tightly linked to En-2. An additional engrailed-like gene known as En-1 exists in mice and is located on chromosome 1 (5). Since the regions of chromosomes 1 and 5 that contained En-1 and -2 are believed to be paralagous, we investigated whether Gbx-2 is located on chromosome 1 in tight linkage with En-1. To accomplish this, an RFLV was found for En-1 using TaqI, fragments of 1.7 kb (C57Bl/10) and 4.6 kb (M. spretus) were observed. The segregation patterns of Gbx-2 and En-1 were found to be identical to each other in the 30 mice examined (Table 1). These results indicate that Gbx-1 and Gbx-2 are tightly linked to En-2 and En-1, respectively. En-1 and En-2 are themselves tightly linked to nearby genes that influence normal development, the mutants Dominant hemimelia (Dh; ref. 7) and Hemimelic extra-toes (Hx; ref. 8), respectively, but are not allelic with them (Fig. 2, see ref. 9). DISCUSSION The portions of chromosomes 1 and 5 that contain Dh and En-1, and Hx and En-2, respectively, were proposed previously to represent paralogous regions (9). The findings presented here provide additional evidence in support of this hypothesis. Embryonic patterns of expression have been determined for Gbx-1 and -2. In particular, Gbx-2 is expressed in the primitive streak during gastrulation, along the anteroposterior axis caudal to the midbrain during early organogenesis, and in the medial portion of the otocyst, which develops into the endolymphatic sac and duct (1). Later in development, at El1.5 - 12.5, Gbx-2 is expressed in restricted regions of the midbrain and forebrain (1, 10). In contrast to Gbx-2, Gbx-1 expression is much more limited during this period. Transcripts were detected only in restricted regions of the forebrain at E11.5 (1). Table 1. (Legend). Segregation patterns of Gbx-1, Gbx-2, En-1, and En-2 in interspecies back cross mice. Individual mice were given designations such as A10, A11... G18 in a previous study (6). White boxes indicate that an M. spetus pattern was observed; black boxes indicate that an M. musculus pattern was observed. The mice used for this study were selected at random from a larger panel of 92 mice (6). The dysmorphology reported for Dh includes skeletal abnormalities of the hind limbs and visceral abnormalities such as a genesis of the spleen (7). Hx is characterized by skeletal abnormalities of all four limbs (8). These findings, and the fact that the mutations are dominant, do not encourage the speculation that the phenotypes might result from loss-of-function of Gbx-1 or -2 (1). However, since phenotypic abnormalities resulting from misexpression or overexpression of regulatory genes are unpredictable, the Gbx genes still represent candidates for these mutant alleles. REFERENCES 1. Frohman, M.A. et al. in preparation. 2. Fainsod et al. (1989) FEBS Lett 250:381-7. 3. Murtha et al. (1991) PNAS 88:10711-5. 4. Joyner and Martin (1987) Genes and Dev. 1:29-38. 5. Joyner et al. (1985) Cell 43:29-37. 6. Van der Meer-de Jong et al. (1990) Genomics 7:270-5. 7. Searle (1964) Genet. Res. 5:171-197. 8. Dickie (1968) Mouse News Lett. 38:24. 9. Martin et al. (1990) Genomics 6:302-308. 10. Bulfone, A. et al. J. Neuroscience, in press. This work was supported by grants from the NIH to G.R.M. (HD-25331) and to B.H. (R01 EY080000-01). M.A.F. was a Special Fellow of the Leukemia Society of America. Figure 2. (Legend). Map distances are given in cM. Actual positions depicted are illustrative only (not drawn to scale). |
