| First Author | Tang M | Year | 1992 |
| Journal | Mouse Genome | Volume | 90 |
| Issue | 3 | Pages | 441-43 |
| Mgi Jnum | J:2534 | Mgi Id | MGI:51056 |
| Citation | Tang M, et al. (1992) Vitiligo maps to mouse chromosome 6 within or close to the mi locus. Mouse Genome 90(3):441-43 |
| abstractText | Full text of Mouse Genome contribution: VITILIGO MAPS TO MOUSE CHROMOSOME 6 WITHIN OR CLOSE TO THE mi LOCUS. M. Tang1, P.E. Neumann2, B. Kosaras1, B.A. Taylor3, and R.L. Sidman1; 1Division of Neurogenetics, New England Regional Primate Research Center, Harvard Medical School, One Pine Hill Drive, Southborough, MA 01772-9102, USA; 2Department of Neurology, Children's Hospital and Harvard Medical School, Boston, MA 02115, USA. 3The Jackson Laboratory, Bar Harbor, ME 04609, USA. The vitiligo mouse, first observed by E. S. Russell (The Jackson Laboratory, Bar Harbor, ME) as a coat color mutation (gene symbol, vit) in the C57BL/6J inbred strain, has been proposed as an animal model for human progressive depigmentation disorder (1-5). Homozygotes are characterized by white spotting, moderate dilution of pigmentation, and progressive depigmentation of the hair, attributable to functional abnormalities and progressive degeneration of melanocytes in the epidermis and hair follicles (1, 2, 6-8). In the eye, abnormal melanocytes and macrophage-like cells were found throughout the uveal tract (7) coupled with a slow progressive degeneration of photoreceptor cells (9). The retinal pigment epithelium of vit/vit mice is morphologically abnormal well before birth (10), has distorted cell-cycle kinetics postnatally (11) and displays reduced phagosome content during the juvenile period, when rod outer segments are still present (12). The present study maps the vit gene to Chromosome 6, either allelic with or close to the micropthalmia (mi) locus. Failure of complementation between vit and mi alleles was found independently by Lamoreux et al. (13). Materials and Methods Homozygous C57BL/6JLer-vit breeders (3), generously provided by A.B. Lerner (Yale University), were repeatedly crossed to C57BL/6J and DBA/2J to produce congenic strains. Two female C57BL/6J-vit homozygotes at N4 were mated to a single male of the MEV linkage testing stock (14, 15). This male was homozygous for 11 ecotropic MuLV proviruses (Emu-20, 27, 24, 11 & 23, 26, 3, 25, 14 and 21, located on Chromosomes (Chrs)l, 3, 5, 7, 8, 9, 10, 11, and 18, respectively), a(t) (Chr 2) and CaJ (Chr 15), and heterozygous for Hm (Chr 5), Miwh (Chr 6) and d (Chr 9). F2 vit/vit mice were sacrificed by cervical dislocation and the spleens were immediately frozen on dry ice. DNA was extracted from the frozen spleens along with samples from C57BL/6J-+/+ and Fl controls, and digested with PvuII and HindIII. Southern blot filters were hybridized with an Emv-specific probe (pEcB4) as previously described (14). Several other linkage tests were performed with visible phenotype linkage marker stocks, some of which were purchased from The Jackson Laboratory. Results Table 1 summarizes the combined results of crosses within the DBA/2J-vit and C57BL/6J-vit breeding stocks. Segregation analysis revealed no significant difference between the observed frequencies and those expected for an autosomal recessive trait. Table 1. Inheritance of the vit gene Mating type: vit/vit x vit/vit; Number of progeny classified: 205; Number of vit/vit; Observed: 205; Expected: 205. Mating type: vit/vit x +/vit; Number of progeny classified: 334; Number of vit/vit; Observed: 173; Expected: 167. Mating type: vit/vit x +/+; Number of progeny classified: 169; Number of vit/vit; Observed: 0; Expected: 0. Mating type: +/vit x +/vit; Number of progeny classified: 231; Number of vit/vit; Observed: 66; Expected: 57. Seven of 19 offspring from the MEV-CaJ Hm- Miwh a(t) x C57BL/6J-vit/vit mating appeared to carry the Miwh gene. These putative double heterozygotes were cream-gray in color with larger white piebald spots and lighter pigmentation than either parental type. This result suggests noncomplementation of vit and Miwh, which could represent allelism or functional gene interaction. By indirect ophthalmoscopy (Heine, Germany), the retinal pigment epithelium (RPE) of these mice showed unpigmented patches similar to those found in vitiligo homozygotes, Neither Miwh nor vit heterozygotes had patchy hypopigmentation of the RPE. Backcrossing two of these double heterozygotes to C57BL/6J-vit/vit mice yielded 13 progeny, all of which were spotted (X2 = 4.33, p < 0.05). Two distinct coat color patterns were observed: 6 mice had spotted cream-gray coats like the doubly heterozygous parents and 7 had the white-spotted dark gray coats typical of the vitiligo parents. Since all of the mice were spotted, these results support the hypothesis that vit and Miwh are allelic or closely linked. The intercrosses of (MEV x C57BL/6J-vit/vit)Fl hybrids produced 458 offspring, but coat color could be unambiguously classified only for the 228 offspring of matings in which neither parent carried Miwh. In the subset segregating for Miwh, homozygosity for d, especially in the presence of a(t), rendered it difficult to distinguish reliably between three possible classes: double heterozygotes (vit and Miwh), vitiligo homozygotes and vitiligo homozygotes that also carried Miwh. Southern blot analyses with an Emv probe of DNA from 26 vit/vit F2 mice (genotype proved by progeny testing) revealed no evidence of linkage with vit. Linkage analysis with the visible markers was based solely on vit/vit mice. In this cross, none of the visible phenotypic marker loci on chromosomes other than Chr 6 showed significant association with the vit trait. Linkage between the agouti locus (at) and vit, although insignificant (X2 = 3.09), was suggestive. In a different set of four crosses, vitiligo was associated with agouti at the 0.0005 significance level when the data of the four crosses were summed, but this association was not consistent and was present at the 0.05 significance level in only two of these crosses when calculated individually (Table 2). Table 2. Tests of association between nonagouti (a) and vitiligo (vit) in four backcrosses. Dam: C57BL/6J-vit; Sire: (STX/Le-A x B6-vit)F1; N: 105; r: 26.7%; X2: 21.2 (p<0.0001). Dam: (MWT/Le-a(t) x B6-vit)F1; Sire: C57BL/6J-vit; N: 85; r: 38.8%; X2: 3.9 (p<0.05). Dam: C57BL/6J-vit; Sire: (ROP/GnLe-A x B6-vit)F1; N: 109; r: 49.5%; X2: 0.4. Dam: (ROP/GnLe-A x B6-vit)F1; Sire: C57BL/6J-vit; N: 73; r: 54.8%; X2: 0.1. Note: N = sample size; r = maximum likelihood estimate of recombination frequency, assuming the vit phenotype is a single locus trait in these crosses; B6 = C57BL/6J. The Fl hybrids from crosses with MWT/Le used in these backcrosses did not carry the Miwh or Wv mutations. To pursue the hypothesis that vit is linked to loci on Chr 6, a cross and backcross with Lurcher (Lc), a marker locus that does not influence pigmentation, was performed. We classified a total of 126 progeny for coat color and motor behavior from the backcross of (C57BL/6J-Lc/+ x C57BL/6J-vit/ vit)F1-Lc/+ +/vit x C57BL/6J-vit/vit, and obtained 52 Lc, 9 +, 8 Lc vit, and 57 vit Thus, Lc and vit assorted non-randomly (X2 = 67.12, p <0.00001) with a recombination frequency of 13.5 +/- 2.9%. Discussion and Conclusions The apparent failure of complementation between vit and Miwh, independently observed by Lamoreux et al. (13), and linkage of vit to the Lc marker locus on Chr 6, suggest that vit is another mutant allele at the mi locus. The estimate of 13.5% recombination between Lc and vit is not significantly different from the estimated map distance of 12.7 +/- 2.5 cM between Lc and mi (16, p. 447). Other mutant alleles at the mi locus show phenotypic overlap with vit: white spotting, coat color dilution, and either turn gray with age (+/miws) or show more severe progressive depigmentation (Miwh/miws and Miwh/mibw) (17, pp. 274 and 276). Therefore, with some reservations as to what future studies may reveal about the detailed structure of the mi region of Chr 6, it appears appropriate to change the symbol for the vitiligo mutation hereafter to mivit. The association between nonagouti (a) and vitiligo (mivit) may simply represent a statistical fluctuation. However, an interaction between Ay and the mi locus has previously been reported (18). Unlike graying with age (Ga; ref. 19), inheritance of vitiligo, at least in some crosses, is consistent with Mendelian inheritance and does not show maternal effects. Acknowledgement: This work was supported by NEI grants EY06859, EY06631 and NCI grant CA33093. References 1. Bell M, Rheins LA and Nordlund JJ (1984). J Cell Biol 99, 386 (Abstr.) 2. Rheins LA, Palkowski MR, James BS and Nordlund JJ (1986). J Invest Dermatol 86, 539-542. 3. Lerner AB (1986). Personal communication. Mouse News Letter 74, 125. 4. Lerner AB, Shiohara T, Boissy RE, Jacobson KA, Lamoreux ML and Moellman GE (1986). J Invest Dermatol 87, 299-304. 5. Boissy RE and Lamoreux ML. (l988). In Advances in Pigment Cell Research, (Bagnara, JT, ed) pp. 207-218, Alan R Liss, NY. 6. Boissy RE, Moellman GE and Lerner AB (1987). Am J Pathol 127, 380-388. 7. Palkowski MR, Nordlund ML, Rheins LA and Nordlund JJ (1987). Arch Dermatol 123, 1022- 1028. 8. Boissy RE, Beato KE and Nordlund JJ (1991). Am J Pathol 138, 1511-1525. 9. Sidman RL and Neumann PE (1988). Personal communication. Mouse News Letter 81, 60. 10. Smirnakis SM, Tang M and Sidman RL (1991). Invest Ophthal Vis Sci 32, 1056 (Abstr.). 11. Ruiz M, Tang M and Sidman RL (1992). Soc. Neurosci. Abstr. 18 (in press). 12. Kosaras B, Smirnakis SW, Tang M and Sidman RL (1992). Soc. Neurosci. Abstr. 18 (in press). 13. Lamoreux ML, Boissy RE, Womack JE and Nordlund JJ (1992). J Hered (in press). 14. Taylor BA and Rowe L (1989). Genomics 5, 221-232. 15. Taylor BA, Ivey M. and Grieco D (1991). Mouse Genome 89, 576-577. 16. Davisson MT, Roderick TH and Doolittle DP (1989). In Genetic Variants and Strains of the Laboratory Mouse, 2nd ed. (Lyon MF and Searle AG, eds) pp. 432-505, Oxford Univ. Press, NY. 17. Silvers W (1979). The Coat Colors of Mice. Springer-Verlag, NY. 18. Lamoreux ML (1981). J Hered 72, 223-224. 19. Morse HC III, Yetter RA, Stimpfling JH, Pitts OM, Fredrickson TN and Hartley JW (1985). Cell 41, 439-448. |
