International Mammalian Genome Society

The 16th International Mouse Genome Conference (2002)


Y Yada
Ochanomizu University, National Institute of Genetics

1) Yada Y, 2) Masuya H, 3) Makino S, 4) Shiroishi T
1) Ochanomizu University, National Institute of Genetics, 2) RIKEN GSC, 3) National Institute of Genetics, 4) National Institute of Genetics, RIKEN GSC

Recombination induced mutation-4 (Rim4) is a spontaneous mouse mutation that arose in intra-MHC recombinants at National Institute of Genetics, Mishima, Japan. Rim4 heterozygotes have an extra triphalangeal digit on the preaxial side of the digit 1 of the hindlimbs, while homozygotes have two or three extra triphalangeal digits instead of the digit 1 in the fore and hindlimbs. In addition, Rim4 homozygotes exhibit tibial hemimelia and sacralization of the presacral vertebrae. To study the molecular basis underlying Rim4 phenotype, we analyzed the expression patterns of several marker genes in the limb buds of Rim4 embryos. It is known that ectopic expression of Shh and Fgf4 are observed at the anterior margin of the Rim4 limb buds. Their expression, however, is detected in the later stage after the aberration of the limb shape becomes apparent. Therefore, we examined the expression of marker genes in the early-stage limb buds. We found that in Rim4 limb buds the expression domains of Shh, Fgf4 and Gre were shifted anteriorly compared with those of wild type embryos. Furthermore, prior to the ectopic expression of the Shh, Gli1 was ectopically activated in the anterior margin of the Rim4 limb bud. Since upstream genes of Shh, such as dHAND, Gli3 and Alx4 were normally expressed, it is possible that Rim4 gene regulates initial anterior-posterior axis formation of the limb through a novel signaling cascade.

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