Newly acquired peri-telomeric heterochromatin in a transgenic mouse lineage

Karyotypes of an embryonic stem cell line and normal bone marrow and peripheral blood cells from a transgenic mouse lineage, strain 83, exhibit a novel region of constitutive heterochromatin in the peri-telomeric region of chromosome 3. This heterochromatic region co-localizes with the integration site of the transgene, an 11-Mb tandem insertion of a plasmid containing human beta-globin gene sequences, and is inherited in Mendelian fashion. The significance of this finding is discussed, and a nomenclature for such newly acquired heterochromatic regions is suggested.