Formation of heterochromatin regions in transgenic mice

Transgenic mice carrying bovine satellite DNA IV were obtained. The size of the transgene integrated into the mouse genome was approximately 390 kb (a bout 100 transgene copies) as determined by a semiquantitative PCR. Restric tion analysis with isoschizomeric restrictases HpaII and MspI, showed that the alien DNA was methylated. In the genome of a transgenic founder male, t wo integration sites for satellite DNA IY were revealed by in situ hybridiz ation and in situ PCR. These sites are situated on two different chromosome s: in pericentromeric heterochromatin and within a chromosomal arm. In tran sgenic mice, de novo formation of heterochromatin regions (C-block and the CMA(3) disk within the centromeric heterochromatin of another chromosome) w as revealed by C-banding and staining with chromomycin A(3). This formation is not characteristic of mice, because their chromosomes normally contain no interstitial C-blocks or sequences intensely stained by chromomycin A(3) .