The present invention features compositions and methods for introducing, into cells, nucleic acids whose expression results in chromosomal silencing. The nucleic acids are targeted to specific chromosomal regions where they subsequently reduce the expression of deleterious genes, or cause the death of deleterious cells. Where the nucleic acid sequence is a silencing sequence, it may encode an Xist RNA or other non-coding, silencing RNA. Accordingly, the present invention features, inter alia, nucleic acid constructs that include a transgene (e.g., a silencing sequence encoding an Xist RNA or other non-coding RNA that silences a segment of a chromosome) first and second sequences that direct insertion of the silencing sequence into a targeted chromosome and, optionally, a selectable marker.
