SRC and neoplasm: To further investigate the role of HP1a-mediated heterochromatin formation in HDS-induced tumorigenesis, we constructed two more strains of Ras/Src tumor-bearing flies with hs-HP1a, an HP1a transgene overexpressing HP1a by basal activity of the hsp70 promoter, with increased HP1a expression by 20% [25], and HP104/+, HP1a heterozygotes of a null-mutation allele, with decreased HP1a levels by 50% [26], respectively.