Developmental mosaicism may explain spontaneous reappearance of the Axin(Fu) mutation in mice

The Axin(Fu) mutation is caused by an IAP insertion. In a small percentage of mice, the Axin(Fu) mutation disappears and is not observed in the next g eneration. In these mice, [Axin(Fu)]/+, the IAP is absent and Axin(Fu) has reverted to the wild allele. Concomitantly with the loss of IAP, there is w idespread reorganisation of numerous microsatellite loci across the surroun ding region of chromosome. In rare cases, spontaneous reappearance of the m utation can be observed in progeny of [Axin(Fu)]/+ mice. It is revealed her e that reappearance of Axin(Fu) was associated with restoration of the IAP insertion. In such mice, alleles of the surrounding microsatellite loci wer e identical to the alleles observed on chromosomes that carried Axin(Fu). D evelopmental mosaicism can potentially explain spontaneous reappearance of the Axin(Fu) mutation. Mosaicism can also explain other observations includ ing postnatal changes at the Axin locus, unusual segregation in progeny, an d the appearance of [Axin(Fu)]/+ mice that were phenotypically mutant. gene sis 29:49-54, 2001, (C) 2001 Wiley-Liss, Inc.