Characterization of HP1 Double-Mutants in Drosophila melanogaster

Many proteins are involved in maintaining chromatin states, including the Heterochromatin Protein 1 (HP1) family. Drosophila melanogaster has three somatic homologs of the HP1 family: HP1a, HP1B, and HP1C. The effects of removing individual HP1 homologs has been investigated; however, little research has been performed on the loss of multiple HP1 proteins. We generated double-mutant fly strains lacking pairwise combinations of the HP1 proteins and investigated the impact of this manipulation. HP1B/HP1C double-mutant third instar larvae had a 7.8% and 15% survival rate, depending on the HP1b allele used. Of these surviving double-mutant larvae, 2.4% and 8.3% survived to the adult stage, again depending on the specific HP1b allele uses. These data illustrate that, although detrimental to the overall health of the flies, complete loss of HP1B and HP1C is survivable in D. melanogaster, raising the possibility that other HP1 family members may compensate for their loss. Ongoing studies focus on HP1a/HP1B/HP1C double-mutants at earlier stages of development to determine at which stage most animals die and on the HP1a/HP1C double-mutants. Our study highlights possible crosstalk and cooperative functions between HP1 proteins, and future studies will provide insights into the potentially overlapping functions of HP1 homologs.